Internet DRAFT - draft-ietf-detnet-use-cases
draft-ietf-detnet-use-cases
Internet Engineering Task Force E. Grossman, Ed.
Internet-Draft DOLBY
Intended status: Informational December 19, 2018
Expires: June 22, 2019
Deterministic Networking Use Cases
draft-ietf-detnet-use-cases-20
Abstract
This draft presents use cases from diverse industries which have in
common a need for "deterministic flows". "Deterministic" in this
context means that such flows provide guaranteed bandwidth, bounded
latency, and other properties germane to the transport of time-
sensitive data. These use cases differ notably in their network
topologies and specific desired behavior, providing as a group broad
industry context for DetNet. For each use case, this document will
identify the use case, identify representative solutions used today,
and describe potential improvements that DetNet can enable. The Use
Case Common Themes section then extracts and enumerates the set of
common properties implied by these use cases.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 22, 2019.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
Grossman Expires June 22, 2019 [Page 1]
Internet-Draft DetNet Use Cases December 2018
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Pro Audio and Video . . . . . . . . . . . . . . . . . . . . . 7
2.1. Use Case Description . . . . . . . . . . . . . . . . . . 7
2.1.1. Uninterrupted Stream Playback . . . . . . . . . . . . 7
2.1.2. Synchronized Stream Playback . . . . . . . . . . . . 8
2.1.3. Sound Reinforcement . . . . . . . . . . . . . . . . . 8
2.1.4. Secure Transmission . . . . . . . . . . . . . . . . . 9
2.1.4.1. Safety . . . . . . . . . . . . . . . . . . . . . 9
2.2. Pro Audio Today . . . . . . . . . . . . . . . . . . . . . 9
2.3. Pro Audio Future . . . . . . . . . . . . . . . . . . . . 9
2.3.1. Layer 3 Interconnecting Layer 2 Islands . . . . . . . 9
2.3.2. High Reliability Stream Paths . . . . . . . . . . . . 10
2.3.3. Integration of Reserved Streams into IT Networks . . 10
2.3.4. Use of Unused Reservations by Best-Effort Traffic . . 10
2.3.5. Traffic Segregation . . . . . . . . . . . . . . . . . 11
2.3.5.1. Packet Forwarding Rules, VLANs and Subnets . . . 11
2.3.5.2. Multicast Addressing (IPv4 and IPv6) . . . . . . 11
2.3.6. Latency Optimization by a Central Controller . . . . 12
2.3.7. Reduced Device Cost Due To Reduced Buffer Memory . . 12
2.4. Pro Audio Asks . . . . . . . . . . . . . . . . . . . . . 12
3. Electrical Utilities . . . . . . . . . . . . . . . . . . . . 13
3.1. Use Case Description . . . . . . . . . . . . . . . . . . 13
3.1.1. Transmission Use Cases . . . . . . . . . . . . . . . 13
3.1.1.1. Protection . . . . . . . . . . . . . . . . . . . 13
3.1.1.2. Intra-Substation Process Bus Communications . . . 18
3.1.1.3. Wide Area Monitoring and Control Systems . . . . 19
3.1.1.4. IEC 61850 WAN engineering guidelines requirement
classification . . . . . . . . . . . . . . . . . 20
3.1.2. Generation Use Case . . . . . . . . . . . . . . . . . 21
3.1.2.1. Control of the Generated Power . . . . . . . . . 21
3.1.2.2. Control of the Generation Infrastructure . . . . 22
3.1.3. Distribution use case . . . . . . . . . . . . . . . . 27
3.1.3.1. Fault Location Isolation and Service Restoration
(FLISR) . . . . . . . . . . . . . . . . . . . . . 27
3.2. Electrical Utilities Today . . . . . . . . . . . . . . . 28
3.2.1. Security Current Practices and Limitations . . . . . 28
3.3. Electrical Utilities Future . . . . . . . . . . . . . . . 30
3.3.1. Migration to Packet-Switched Network . . . . . . . . 31
3.3.2. Telecommunications Trends . . . . . . . . . . . . . . 31
Grossman Expires June 22, 2019 [Page 2]
Internet-Draft DetNet Use Cases December 2018
3.3.2.1. General Telecommunications Requirements . . . . . 31
3.3.2.2. Specific Network topologies of Smart Grid
Applications . . . . . . . . . . . . . . . . . . 32
3.3.2.3. Precision Time Protocol . . . . . . . . . . . . . 33
3.3.3. Security Trends in Utility Networks . . . . . . . . . 34
3.4. Electrical Utilities Asks . . . . . . . . . . . . . . . . 36
4. Building Automation Systems . . . . . . . . . . . . . . . . . 36
4.1. Use Case Description . . . . . . . . . . . . . . . . . . 36
4.2. Building Automation Systems Today . . . . . . . . . . . . 37
4.2.1. BAS Architecture . . . . . . . . . . . . . . . . . . 37
4.2.2. BAS Deployment Model . . . . . . . . . . . . . . . . 38
4.2.3. Use Cases for Field Networks . . . . . . . . . . . . 40
4.2.3.1. Environmental Monitoring . . . . . . . . . . . . 40
4.2.3.2. Fire Detection . . . . . . . . . . . . . . . . . 40
4.2.3.3. Feedback Control . . . . . . . . . . . . . . . . 41
4.2.4. Security Considerations . . . . . . . . . . . . . . . 41
4.3. BAS Future . . . . . . . . . . . . . . . . . . . . . . . 41
4.4. BAS Asks . . . . . . . . . . . . . . . . . . . . . . . . 42
5. Wireless for Industrial Applications . . . . . . . . . . . . 42
5.1. Use Case Description . . . . . . . . . . . . . . . . . . 42
5.1.1. Network Convergence using 6TiSCH . . . . . . . . . . 43
5.1.2. Common Protocol Development for 6TiSCH . . . . . . . 43
5.2. Wireless Industrial Today . . . . . . . . . . . . . . . . 44
5.3. Wireless Industrial Future . . . . . . . . . . . . . . . 44
5.3.1. Unified Wireless Network and Management . . . . . . . 44
5.3.1.1. PCE and 6TiSCH ARQ Retries . . . . . . . . . . . 46
5.3.2. Schedule Management by a PCE . . . . . . . . . . . . 47
5.3.2.1. PCE Commands and 6TiSCH CoAP Requests . . . . . . 47
5.3.2.2. 6TiSCH IP Interface . . . . . . . . . . . . . . . 48
5.3.3. 6TiSCH Security Considerations . . . . . . . . . . . 49
5.4. Wireless Industrial Asks . . . . . . . . . . . . . . . . 49
6. Cellular Radio . . . . . . . . . . . . . . . . . . . . . . . 49
6.1. Use Case Description . . . . . . . . . . . . . . . . . . 49
6.1.1. Network Architecture . . . . . . . . . . . . . . . . 49
6.1.2. Delay Constraints . . . . . . . . . . . . . . . . . . 50
6.1.3. Time Synchronization Constraints . . . . . . . . . . 52
6.1.4. Transport Loss Constraints . . . . . . . . . . . . . 54
6.1.5. Security Considerations . . . . . . . . . . . . . . . 54
6.2. Cellular Radio Networks Today . . . . . . . . . . . . . . 55
6.2.1. Fronthaul . . . . . . . . . . . . . . . . . . . . . . 55
6.2.2. Midhaul and Backhaul . . . . . . . . . . . . . . . . 55
6.3. Cellular Radio Networks Future . . . . . . . . . . . . . 56
6.4. Cellular Radio Networks Asks . . . . . . . . . . . . . . 58
7. Industrial Machine to Machine (M2M) . . . . . . . . . . . . . 59
7.1. Use Case Description . . . . . . . . . . . . . . . . . . 59
7.2. Industrial M2M Communication Today . . . . . . . . . . . 60
7.2.1. Transport Parameters . . . . . . . . . . . . . . . . 60
7.2.2. Stream Creation and Destruction . . . . . . . . . . . 61
Grossman Expires June 22, 2019 [Page 3]
Internet-Draft DetNet Use Cases December 2018
7.3. Industrial M2M Future . . . . . . . . . . . . . . . . . . 61
7.4. Industrial M2M Asks . . . . . . . . . . . . . . . . . . . 62
8. Mining Industry . . . . . . . . . . . . . . . . . . . . . . . 62
8.1. Use Case Description . . . . . . . . . . . . . . . . . . 62
8.2. Mining Industry Today . . . . . . . . . . . . . . . . . . 63
8.3. Mining Industry Future . . . . . . . . . . . . . . . . . 63
8.4. Mining Industry Asks . . . . . . . . . . . . . . . . . . 64
9. Private Blockchain . . . . . . . . . . . . . . . . . . . . . 64
9.1. Use Case Description . . . . . . . . . . . . . . . . . . 64
9.1.1. Blockchain Operation . . . . . . . . . . . . . . . . 65
9.1.2. Blockchain Network Architecture . . . . . . . . . . . 65
9.1.3. Security Considerations . . . . . . . . . . . . . . . 66
9.2. Private Blockchain Today . . . . . . . . . . . . . . . . 66
9.3. Private Blockchain Future . . . . . . . . . . . . . . . . 66
9.4. Private Blockchain Asks . . . . . . . . . . . . . . . . . 67
10. Network Slicing . . . . . . . . . . . . . . . . . . . . . . . 67
10.1. Use Case Description . . . . . . . . . . . . . . . . . . 67
10.2. DetNet Applied to Network Slicing . . . . . . . . . . . 67
10.2.1. Resource Isolation Across Slices . . . . . . . . . . 67
10.2.2. Deterministic Services Within Slices . . . . . . . . 68
10.3. A Network Slicing Use Case Example - 5G Bearer Network . 68
10.4. Non-5G Applications of Network Slicing . . . . . . . . . 69
10.5. Limitations of DetNet in Network Slicing . . . . . . . . 69
10.6. Network Slicing Today and Future . . . . . . . . . . . . 69
10.7. Network Slicing Asks . . . . . . . . . . . . . . . . . . 69
11. Use Case Common Themes . . . . . . . . . . . . . . . . . . . 69
11.1. Unified, standards-based network . . . . . . . . . . . . 70
11.1.1. Extensions to Ethernet . . . . . . . . . . . . . . . 70
11.1.2. Centrally Administered . . . . . . . . . . . . . . . 70
11.1.3. Standardized Data Flow Information Models . . . . . 70
11.1.4. L2 and L3 Integration . . . . . . . . . . . . . . . 70
11.1.5. Consideration for IPv4 . . . . . . . . . . . . . . . 70
11.1.6. Guaranteed End-to-End Delivery . . . . . . . . . . . 71
11.1.7. Replacement for Multiple Proprietary Deterministic
Networks . . . . . . . . . . . . . . . . . . . . . . 71
11.1.8. Mix of Deterministic and Best-Effort Traffic . . . . 71
11.1.9. Unused Reserved BW to be Available to Best-Effort
Traffic . . . . . . . . . . . . . . . . . . . . . . 71
11.1.10. Lower Cost, Multi-Vendor Solutions . . . . . . . . . 71
11.2. Scalable Size . . . . . . . . . . . . . . . . . . . . . 71
11.2.1. Scalable Number of Flows . . . . . . . . . . . . . . 72
11.3. Scalable Timing Parameters and Accuracy . . . . . . . . 72
11.3.1. Bounded Latency . . . . . . . . . . . . . . . . . . 72
11.3.2. Low Latency . . . . . . . . . . . . . . . . . . . . 72
11.3.3. Bounded Jitter (Latency Variation) . . . . . . . . . 72
11.3.4. Symmetrical Path Delays . . . . . . . . . . . . . . 72
11.4. High Reliability and Availability . . . . . . . . . . . 73
11.5. Security . . . . . . . . . . . . . . . . . . . . . . . . 73
Grossman Expires June 22, 2019 [Page 4]
Internet-Draft DetNet Use Cases December 2018
11.6. Deterministic Flows . . . . . . . . . . . . . . . . . . 73
12. Security Considerations . . . . . . . . . . . . . . . . . . . 73
13. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 74
14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 75
14.1. Pro Audio . . . . . . . . . . . . . . . . . . . . . . . 75
14.2. Utility Telecom . . . . . . . . . . . . . . . . . . . . 76
14.3. Building Automation Systems . . . . . . . . . . . . . . 76
14.4. Wireless for Industrial Applications . . . . . . . . . . 76
14.5. Cellular Radio . . . . . . . . . . . . . . . . . . . . . 76
14.6. Industrial Machine to Machine (M2M) . . . . . . . . . . 77
14.7. Internet Applications and CoMP . . . . . . . . . . . . . 77
14.8. Network Slicing . . . . . . . . . . . . . . . . . . . . 77
14.9. Mining . . . . . . . . . . . . . . . . . . . . . . . . . 77
14.10. Private Blockchain . . . . . . . . . . . . . . . . . . . 77
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 77
16. Informative References . . . . . . . . . . . . . . . . . . . 77
Appendix A. Use Cases Explicitly Out of Scope for DetNet . . . . 84
A.1. DetNet Scope Limitations . . . . . . . . . . . . . . . . 85
A.2. Internet-based Applications . . . . . . . . . . . . . . . 85
A.2.1. Use Case Description . . . . . . . . . . . . . . . . 86
A.2.1.1. Media Content Delivery . . . . . . . . . . . . . 86
A.2.1.2. Online Gaming . . . . . . . . . . . . . . . . . . 86
A.2.1.3. Virtual Reality . . . . . . . . . . . . . . . . . 86
A.2.2. Internet-Based Applications Today . . . . . . . . . . 86
A.2.3. Internet-Based Applications Future . . . . . . . . . 86
A.2.4. Internet-Based Applications Asks . . . . . . . . . . 86
A.3. Pro Audio and Video - Digital Rights Management (DRM) . . 87
A.4. Pro Audio and Video - Link Aggregation . . . . . . . . . 87
A.5. Pro Audio and Video - Deterministic Time to Establish
Streaming . . . . . . . . . . . . . . . . . . . . . . . . 87
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 88
1. Introduction
This draft documents use cases in diverse industries which require
deterministic flows over multi-hop paths. DetNet flows can be
established from either a Layer 2 or Layer 3 (IP) interface, and such
flows can co-exist on an IP network with best-effort traffic. DetNet
also provides for highly reliable flows through provision for
redundant paths.
The DetNet Use Cases explicitly do not suggest any specific design
for DetNet architecture or protocols; these are topics of other
DetNet drafts.
The DetNet use cases as originally submitted explicitly were not
considered by the DetNet Working Group to be concrete requirements;
The DetNet Working Group and Design Team considered these use cases,
Grossman Expires June 22, 2019 [Page 5]
Internet-Draft DetNet Use Cases December 2018
identifying which elements of them could be feasibly implemented
within the charter of DetNet, and as a result certain of the
originally submitted use cases (or elements of them) have been be
moved to the Use Cases Explicitly Out of Scope for DetNet section.
The DetNet Use Cases document provide context regarding DetNet design
decisions. It also serves a long-lived purpose of helping those
learning (or new to) DetNet to understand the types of applications
that can be supported by DetNet. It also allow those WG contributors
who are users to ensure that their concerns are addressed by the WG;
for them this document both covers their contribution and provides a
long term reference to the problems they expect to be served by the
technology, both in the short term deliverables and as the technology
evolves in the future.
The DetNet Use Cases document has served as a "yardstick" against
which proposed DetNet designs can be measured, answering the question
"to what extent does a proposed design satisfy these various use
cases?"
The Use Case industries covered are professional audio, electrical
utilities, building automation systems, wireless for industrial
applications, cellular radio, industrial machine-to-machine, mining,
private blockchain, and network slicing. For each use case the
following questions are answered:
o What is the use case?
o How is it addressed today?
o How should it be addressed in the future?
o What should the IETF deliver to enable this use case?
The level of detail in each use case is intended to be sufficient to
express the relevant elements of the use case, but not greater than
that.
DetNet does not directly address clock distribution or time
synchronization; these are considered to be part of the overall
design and implementation of a time-sensitive network, using existing
(or future) time-specific protocols (such as [IEEE8021AS] and/or
[RFC5905]).
Grossman Expires June 22, 2019 [Page 6]
Internet-Draft DetNet Use Cases December 2018
2. Pro Audio and Video
2.1. Use Case Description
The professional audio and video industry ("ProAV") includes:
o Music and film content creation
o Broadcast
o Cinema
o Live sound
o Public address, media and emergency systems at large venues
(airports, stadiums, churches, theme parks).
These industries have already transitioned audio and video signals
from analog to digital. However, the digital interconnect systems
remain primarily point-to-point with a single (or small number of)
signals per link, interconnected with purpose-built hardware.
These industries are now transitioning to packet-based infrastructure
to reduce cost, increase routing flexibility, and integrate with
existing IT infrastructure.
Today ProAV applications have no way to establish deterministic flows
from a standards-based Layer 3 (IP) interface, which is a fundamental
limitation to the use cases described here. Today deterministic
flows can be created within standards-based layer 2 LANs (e.g. using
IEEE 802.1 AVB) however these are not routable via IP and thus are
not effective for distribution over wider areas (for example
broadcast events that span wide geographical areas).
It would be highly desirable if such flows could be routed over the
open Internet, however solutions with more limited scope (e.g.
enterprise networks) would still provide a substantial improvement.
The following sections describe specific ProAV use cases.
2.1.1. Uninterrupted Stream Playback
Transmitting audio and video streams for live playback is unlike
common file transfer because uninterrupted stream playback in the
presence of network errors cannot be achieved by re-trying the
transmission; by the time the missing or corrupt packet has been
identified it is too late to execute a re-try operation. Buffering
can be used to provide enough delay to allow time for one or more
Grossman Expires June 22, 2019 [Page 7]
Internet-Draft DetNet Use Cases December 2018
retries, however this is not an effective solution in applications
where large delays (latencies) are not acceptable (as discussed
below).
Streams with guaranteed bandwidth can eliminate congestion on the
network as a cause of transmission errors that would lead to playback
interruption. Use of redundant paths can further mitigate
transmission errors to provide greater stream reliability.
Additional techniques such as forward error correction can also be
used to improve stream reliability.
2.1.2. Synchronized Stream Playback
Latency in this context is the time between when a signal is
initially sent over a stream and when it is received. A common
example in ProAV is time-synchronizing audio and video when they take
separate paths through the playback system. In this case the latency
of both the audio and video streams must be bounded and consistent if
the sound is to remain matched to the movement in the video. A
common tolerance for audio/video sync is one NTSC video frame (about
33ms) and to maintain the audience perception of correct lip sync the
latency needs to be consistent within some reasonable tolerance, for
example 10%.
A common architecture for synchronizing multiple streams that have
different paths through the network (and thus potentially different
latencies) is to enable measurement of the latency of each path, and
have the data sinks (for example speakers) delay (buffer) all packets
on all but the slowest path. Each packet of each stream is assigned
a presentation time which is based on the longest required delay.
This implies that all sinks must maintain a common time reference of
sufficient accuracy, which can be achieved by any of various
techniques.
This type of architecture is commonly implemented using a central
controller that determines path delays and arbitrates buffering
delays.
2.1.3. Sound Reinforcement
Consider the latency (delay) from when a person speaks into a
microphone to when their voice emerges from the speaker. If this
delay is longer than about 10-15 milliseconds it is noticeable and
can make a sound reinforcement system unusable (see slide 6 of
[SRP_LATENCY]). (If you have ever tried to speak in the presence of
a delayed echo of your voice you may know this experience).
Grossman Expires June 22, 2019 [Page 8]
Internet-Draft DetNet Use Cases December 2018
Note that the 15ms latency bound includes all parts of the signal
path, not just the network, so the network latency must be
significantly less than 15ms.
In some cases local performers must perform in synchrony with a
remote broadcast. In such cases the latencies of the broadcast
stream and the local performer must be adjusted to match each other,
with a worst case of one video frame (33ms for NTSC video).
In cases where audio phase is a consideration, for example beam-
forming using multiple speakers, latency can be in the 10 microsecond
range (1 audio sample at 96kHz).
2.1.4. Secure Transmission
2.1.4.1. Safety
Professional audio systems can include amplifiers that are capable of
generating hundreds or thousands of watts of audio power which if
used incorrectly can cause hearing damage to those in the vicinity.
Apart from the usual care required by the systems operators to
prevent such incidents, the network traffic that controls these
devices must be secured (as with any sensitive application traffic).
2.2. Pro Audio Today
Some proprietary systems have been created which enable deterministic
streams at Layer 3 however they are "engineered networks" which
require careful configuration to operate, often require that the
system be over-provisioned, and it is implied that all devices on the
network voluntarily play by the rules of that network. To enable
these industries to successfully transition to an interoperable
multi-vendor packet-based infrastructure requires effective open
standards, and establishing relevant IETF standards is a crucial
factor.
2.3. Pro Audio Future
2.3.1. Layer 3 Interconnecting Layer 2 Islands
It would be valuable to enable IP to connect multiple Layer 2 LANs.
As an example, ESPN constructed a state-of-the-art 194,000 sq ft,
$125 million broadcast studio called DC2. The DC2 network is capable
of handling 46 Tbps of throughput with 60,000 simultaneous signals.
Inside the facility are 1,100 miles of fiber feeding four audio
control rooms (see [ESPN_DC2] ).
Grossman Expires June 22, 2019 [Page 9]
Internet-Draft DetNet Use Cases December 2018
In designing DC2 they replaced as much point-to-point technology as
they could with packet-based technology. They constructed seven
individual studios using layer 2 LANS (using IEEE 802.1 AVB) that
were entirely effective at routing audio within the LANs. However to
interconnect these layer 2 LAN islands together they ended up using
dedicated paths in a custom SDN (Software Defined Networking) router
because there is no standards-based routing solution available.
2.3.2. High Reliability Stream Paths
On-air and other live media streams are often backed up with
redundant links that seamlessly act to deliver the content when the
primary link fails for any reason. In point-to-point systems this is
provided by an additional point-to-point link; the analogous
requirement in a packet-based system is to provide an alternate path
through the network such that no individual link can bring down the
system.
2.3.3. Integration of Reserved Streams into IT Networks
A commonly cited goal of moving to a packet based media
infrastructure is that costs can be reduced by using off the shelf,
commodity network hardware. In addition, economy of scale can be
realized by combining media infrastructure with IT infrastructure.
In keeping with these goals, stream reservation technology should be
compatible with existing protocols, and not compromise use of the
network for best-effort (non-time-sensitive) traffic.
2.3.4. Use of Unused Reservations by Best-Effort Traffic
In cases where stream bandwidth is reserved but not currently used
(or is under-utilized) that bandwidth must be available to best-
effort (i.e. non-time-sensitive) traffic. For example a single
stream may be nailed up (reserved) for specific media content that
needs to be presented at different times of the day, ensuring timely
delivery of that content, yet in between those times the full
bandwidth of the network can be utilized for best-effort tasks such
as file transfers.
This also addresses a concern of IT network administrators that are
considering adding reserved bandwidth traffic to their networks that
"users will reserve large quantities of bandwidth and then never un-
reserve it even though they are not using it, and soon the network
will have no bandwidth left".
Grossman Expires June 22, 2019 [Page 10]
Internet-Draft DetNet Use Cases December 2018
2.3.5. Traffic Segregation
Sink devices may be low cost devices with limited processing power.
In order to not overwhelm the CPUs in these devices it is important
to limit the amount of traffic that these devices must process.
As an example, consider the use of individual seat speakers in a
cinema. These speakers are typically required to be cost reduced
since the quantities in a single theater can reach hundreds of seats.
Discovery protocols alone in a one thousand seat theater can generate
enough broadcast traffic to overwhelm a low powered CPU. Thus an
installation like this will benefit greatly from some type of traffic
segregation that can define groups of seats to reduce traffic within
each group. All seats in the theater must still be able to
communicate with a central controller.
There are many techniques that can be used to support this feature
including (but not limited to) the following examples.
2.3.5.1. Packet Forwarding Rules, VLANs and Subnets
Packet forwarding rules can be used to eliminate some extraneous
streaming traffic from reaching potentially low powered sink devices,
however there may be other types of broadcast traffic that should be
eliminated using other means for example VLANs or IP subnets.
2.3.5.2. Multicast Addressing (IPv4 and IPv6)
Multicast addressing is commonly used to keep bandwidth utilization
of shared links to a minimum.
Because of the MAC Address forwarding nature of Layer 2 bridges it is
important that a multicast MAC address is only associated with one
stream. This will prevent reservations from forwarding packets from
one stream down a path that has no interested sinks simply because
there is another stream on that same path that shares the same
multicast MAC address.
Since each multicast MAC Address can represent 32 different IPv4
multicast addresses there must be a process put in place to make sure
this does not occur. Requiring use of IPv6 address can achieve this,
however due to their continued prevalence, solutions that are
effective for IPv4 installations are also desirable.
Grossman Expires June 22, 2019 [Page 11]
Internet-Draft DetNet Use Cases December 2018
2.3.6. Latency Optimization by a Central Controller
A central network controller might also perform optimizations based
on the individual path delays, for example sinks that are closer to
the source can inform the controller that they can accept greater
latency since they will be buffering packets to match presentation
times of farther away sinks. The controller might then move a stream
reservation on a short path to a longer path in order to free up
bandwidth for other critical streams on that short path. See slides
3-5 of [SRP_LATENCY].
Additional optimization can be achieved in cases where sinks have
differing latency requirements, for example in a live outdoor concert
the speaker sinks have stricter latency requirements than the
recording hardware sinks. See slide 7 of [SRP_LATENCY].
2.3.7. Reduced Device Cost Due To Reduced Buffer Memory
Device cost can be reduced in a system with guaranteed reservations
with a small bounded latency due to the reduced requirements for
buffering (i.e. memory) on sink devices. For example, a theme park
might broadcast a live event across the globe via a layer 3 protocol;
in such cases the size of the buffers required is proportional to the
latency bounds and jitter caused by delivery, which depends on the
worst case segment of the end-to-end network path. For example on
todays open internet the latency is typically unacceptable for audio
and video streaming without many seconds of buffering. In such
scenarios a single gateway device at the local network that receives
the feed from the remote site would provide the expensive buffering
required to mask the latency and jitter issues associated with long
distance delivery. Sink devices in the local location would have no
additional buffering requirements, and thus no additional costs,
beyond those required for delivery of local content. The sink device
would be receiving the identical packets as those sent by the source
and would be unaware that there were any latency or jitter issues
along the path.
2.4. Pro Audio Asks
o Layer 3 routing on top of AVB (and/or other high QoS networks)
o Content delivery with bounded, lowest possible latency
o IntServ and DiffServ integration with AVB (where practical)
o Single network for A/V and IT traffic
o Standards-based, interoperable, multi-vendor
Grossman Expires June 22, 2019 [Page 12]
Internet-Draft DetNet Use Cases December 2018
o IT department friendly
o Enterprise-wide networks (e.g. size of San Francisco but not the
whole Internet (yet...))
3. Electrical Utilities
3.1. Use Case Description
Many systems that an electrical utility deploys today rely on high
availability and deterministic behavior of the underlying networks.
Presented here are use cases in Transmission, Generation and
Distribution, including key timing and reliability metrics. In
addition, security issues and industry trends which affect the
architecture of next generation utility networks are discussed.
3.1.1. Transmission Use Cases
3.1.1.1. Protection
Protection means not only the protection of human operators but also
the protection of the electrical equipment and the preservation of
the stability and frequency of the grid. If a fault occurs in the
transmission or distribution of electricity then severe damage can
occur to human operators, electrical equipment and the grid itself,
leading to blackouts.
Communication links in conjunction with protection relays are used to
selectively isolate faults on high voltage lines, transformers,
reactors and other important electrical equipment. The role of the
teleprotection system is to selectively disconnect a faulty part by
transferring command signals within the shortest possible time.
3.1.1.1.1. Key Criteria
The key criteria for measuring teleprotection performance are command
transmission time, dependability and security. These criteria are
defined by the IEC standard 60834 as follows:
o Transmission time (Speed): The time between the moment where state
changes at the transmitter input and the moment of the
corresponding change at the receiver output, including propagation
delay. Overall operating time for a teleprotection system
includes the time for initiating the command at the transmitting
end, the propagation delay over the network (including equipments)
and the selection and decision time at the receiving end,
including any additional delay due to a noisy environment.
Grossman Expires June 22, 2019 [Page 13]
Internet-Draft DetNet Use Cases December 2018
o Dependability: The ability to issue and receive valid commands in
the presence of interference and/or noise, by minimizing the
probability of missing command (PMC). Dependability targets are
typically set for a specific bit error rate (BER) level.
o Security: The ability to prevent false tripping due to a noisy
environment, by minimizing the probability of unwanted commands
(PUC). Security targets are also set for a specific bit error
rate (BER) level.
Additional elements of the teleprotection system that impact its
performance include:
o Network bandwidth
o Failure recovery capacity (aka resiliency)
3.1.1.1.2. Fault Detection and Clearance Timing
Most power line equipment can tolerate short circuits or faults for
up to approximately five power cycles before sustaining irreversible
damage or affecting other segments in the network. This translates
to total fault clearance time of 100ms. As a safety precaution,
however, actual operation time of protection systems is limited to
70- 80 percent of this period, including fault recognition time,
command transmission time and line breaker switching time.
Some system components, such as large electromechanical switches,
require particularly long time to operate and take up the majority of
the total clearance time, leaving only a 10ms window for the
telecommunications part of the protection scheme, independent of the
distance to travel. Given the sensitivity of the issue, new networks
impose requirements that are even more stringent: IEC standard 61850
limits the transfer time for protection messages to 1/4 - 1/2 cycle
or 4 - 8ms (for 60Hz lines) for the most critical messages.
3.1.1.1.3. Symmetric Channel Delay
Teleprotection channels which are differential must be synchronous,
which means that any delays on the transmit and receive paths must
match each other. Teleprotection systems ideally support zero
asymmetric delay; typical legacy relays can tolerate delay
discrepancies of up to 750us.
Some tools available for lowering delay variation below this
threshold are:
Grossman Expires June 22, 2019 [Page 14]
Internet-Draft DetNet Use Cases December 2018
o For legacy systems using Time Division Multiplexing (TDM), jitter
buffers at the multiplexers on each end of the line can be used to
offset delay variation by queuing sent and received packets. The
length of the queues must balance the need to regulate the rate of
transmission with the need to limit overall delay, as larger
buffers result in increased latency.
o For jitter-prone IP packet networks, traffic management tools can
ensure that the teleprotection signals receive the highest
transmission priority to minimize jitter.
o Standard packet-based synchronization technologies, such as
1588-2008 Precision Time Protocol (PTP) and Synchronous Ethernet
(Sync-E), can help keep networks stable by maintaining a highly
accurate clock source on the various network devices.
3.1.1.1.4. Teleprotection Network Requirements (IEC 61850)
The following table captures the main network metrics as based on the
IEC 61850 standard.
+-----------------------------+-------------------------------------+
| Teleprotection Requirement | Attribute |
+-----------------------------+-------------------------------------+
| One way maximum delay | 4-10 ms |
| Asymetric delay required | Yes |
| Maximum jitter | less than 250 us (750 us for legacy |
| | IED) |
| Topology | Point to point, point to Multi- |
| | point |
| Availability | 99.9999 |
| precise timing required | Yes |
| Recovery time on node | less than 50ms - hitless |
| failure | |
| performance management | Yes, Mandatory |
| Redundancy | Yes |
| Packet loss | 0.1% to 1% |
+-----------------------------+-------------------------------------+
Table 1: Teleprotection network requirements
3.1.1.1.5. Inter-Trip Protection scheme
"Inter-tripping" is the signal-controlled tripping of a circuit
breaker to complete the isolation of a circuit or piece of apparatus
in concert with the tripping of other circuit breakers.
Grossman Expires June 22, 2019 [Page 15]
Internet-Draft DetNet Use Cases December 2018
+--------------------------------+----------------------------------+
| Inter-Trip protection | Attribute |
| Requirement | |
+--------------------------------+----------------------------------+
| One way maximum delay | 5 ms |
| Asymetric delay required | No |
| Maximum jitter | Not critical |
| Topology | Point to point, point to Multi- |
| | point |
| Bandwidth | 64 Kbps |
| Availability | 99.9999 |
| precise timing required | Yes |
| Recovery time on node failure | less than 50ms - hitless |
| performance management | Yes, Mandatory |
| Redundancy | Yes |
| Packet loss | 0.1% |
+--------------------------------+----------------------------------+
Table 2: Inter-Trip protection network requirements
3.1.1.1.6. Current Differential Protection Scheme
Current differential protection is commonly used for line protection,
and is typical for protecting parallel circuits. At both end of the
lines the current is measured by the differential relays, and both
relays will trip the circuit breaker if the current going into the
line does not equal the current going out of the line. This type of
protection scheme assumes some form of communications being present
between the relays at both end of the line, to allow both relays to
compare measured current values. Line differential protection
schemes assume a very low telecommunications delay between both
relays, often as low as 5ms. Moreover, as those systems are often
not time-synchronized, they also assume symmetric telecommunications
paths with constant delay, which allows comparing current measurement
values taken at the exact same time.
Grossman Expires June 22, 2019 [Page 16]
Internet-Draft DetNet Use Cases December 2018
+----------------------------------+--------------------------------+
| Current Differential protection | Attribute |
| Requirement | |
+----------------------------------+--------------------------------+
| One way maximum delay | 5 ms |
| Asymetric delay Required | Yes |
| Maximum jitter | less than 250 us (750us for |
| | legacy IED) |
| Topology | Point to point, point to |
| | Multi-point |
| Bandwidth | 64 Kbps |
| Availability | 99.9999 |
| precise timing required | Yes |
| Recovery time on node failure | less than 50ms - hitless |
| performance management | Yes, Mandatory |
| Redundancy | Yes |
| Packet loss | 0.1% |
+----------------------------------+--------------------------------+
Table 3: Current Differential Protection metrics
3.1.1.1.7. Distance Protection Scheme
Distance (Impedance Relay) protection scheme is based on voltage and
current measurements. The network metrics are similar (but not
identical to) Current Differential protection.
+-------------------------------+-----------------------------------+
| Distance protection | Attribute |
| Requirement | |
+-------------------------------+-----------------------------------+
| One way maximum delay | 5 ms |
| Asymetric delay Required | No |
| Maximum jitter | Not critical |
| Topology | Point to point, point to Multi- |
| | point |
| Bandwidth | 64 Kbps |
| Availability | 99.9999 |
| precise timing required | Yes |
| Recovery time on node failure | less than 50ms - hitless |
| performance management | Yes, Mandatory |
| Redundancy | Yes |
| Packet loss | 0.1% |
+-------------------------------+-----------------------------------+
Table 4: Distance Protection requirements
Grossman Expires June 22, 2019 [Page 17]
Internet-Draft DetNet Use Cases December 2018
3.1.1.1.8. Inter-Substation Protection Signaling
This use case describes the exchange of Sampled Value and/or GOOSE
(Generic Object Oriented Substation Events) message between
Intelligent Electronic Devices (IED) in two substations for
protection and tripping coordination. The two IEDs are in a master-
slave mode.
The Current Transformer or Voltage Transformer (CT/VT) in one
substation sends the sampled analog voltage or current value to the
Merging Unit (MU) over hard wire. The MU sends the time-synchronized
61850-9-2 sampled values to the slave IED. The slave IED forwards
the information to the Master IED in the other substation. The
master IED makes the determination (for example based on sampled
value differentials) to send a trip command to the originating IED.
Once the slave IED/Relay receives the GOOSE trip for breaker
tripping, it opens the breaker. It then sends a confirmation message
back to the master. All data exchanges between IEDs are either
through Sampled Value and/or GOOSE messages.
+----------------------------------+--------------------------------+
| Inter-Substation protection | Attribute |
| Requirement | |
+----------------------------------+--------------------------------+
| One way maximum delay | 5 ms |
| Asymetric delay Required | No |
| Maximum jitter | Not critical |
| Topology | Point to point, point to |
| | Multi-point |
| Bandwidth | 64 Kbps |
| Availability | 99.9999 |
| precise timing required | Yes |
| Recovery time on node failure | less than 50ms - hitless |
| performance management | Yes, Mandatory |
| Redundancy | Yes |
| Packet loss | 1% |
+----------------------------------+--------------------------------+
Table 5: Inter-Substation Protection requirements
3.1.1.2. Intra-Substation Process Bus Communications
This use case describes the data flow from the CT/VT to the IEDs in
the substation via the MU. The CT/VT in the substation send the
analog voltage or current values to the MU over hard wire. The MU
converts the analog values into digital format (typically time-
synchronized Sampled Values as specified by IEC 61850-9-2) and sends
them to the IEDs in the substation. The GPS Master Clock can send
Grossman Expires June 22, 2019 [Page 18]
Internet-Draft DetNet Use Cases December 2018
1PPS or IRIG-B format to the MU through a serial port or IEEE 1588
protocol via a network. Process bus communication using 61850
simplifies connectivity within the substation and removes the
requirement for multiple serial connections and removes the slow
serial bus architectures that are typically used. This also ensures
increased flexibility and increased speed with the use of multicast
messaging between multiple devices.
+----------------------------------+--------------------------------+
| Intra-Substation protection | Attribute |
| Requirement | |
+----------------------------------+--------------------------------+
| One way maximum delay | 5 ms |
| Asymetric delay Required | No |
| Maximum jitter | Not critical |
| Topology | Point to point, point to |
| | Multi-point |
| Bandwidth | 64 Kbps |
| Availability | 99.9999 |
| precise timing required | Yes |
| Recovery time on Node failure | less than 50ms - hitless |
| performance management | Yes, Mandatory |
| Redundancy | Yes - No |
| Packet loss | 0.1% |
+----------------------------------+--------------------------------+
Table 6: Intra-Substation Protection requirements
3.1.1.3. Wide Area Monitoring and Control Systems
The application of synchrophasor measurement data from Phasor
Measurement Units (PMU) to Wide Area Monitoring and Control Systems
promises to provide important new capabilities for improving system
stability. Access to PMU data enables more timely situational
awareness over larger portions of the grid than what has been
possible historically with normal SCADA (Supervisory Control and Data
Acquisition) data. Handling the volume and real-time nature of
synchrophasor data presents unique challenges for existing
application architectures. Wide Area management System (WAMS) makes
it possible for the condition of the bulk power system to be observed
and understood in real-time so that protective, preventative, or
corrective action can be taken. Because of the very high sampling
rate of measurements and the strict requirement for time
synchronization of the samples, WAMS has stringent telecommunications
requirements in an IP network that are captured in the following
table:
Grossman Expires June 22, 2019 [Page 19]
Internet-Draft DetNet Use Cases December 2018
+----------------------+--------------------------------------------+
| WAMS Requirement | Attribute |
+----------------------+--------------------------------------------+
| One way maximum | 50 ms |
| delay | |
| Asymetric delay | No |
| Required | |
| Maximum jitter | Not critical |
| Topology | Point to point, point to Multi-point, |
| | Multi-point to Multi-point |
| Bandwidth | 100 Kbps |
| Availability | 99.9999 |
| precise timing | Yes |
| required | |
| Recovery time on | less than 50ms - hitless |
| Node failure | |
| performance | Yes, Mandatory |
| management | |
| Redundancy | Yes |
| Packet loss | 1% |
| Consecutive Packet | At least 1 packet per application cycle |
| Loss | must be received. |
+----------------------+--------------------------------------------+
Table 7: WAMS Special Communication Requirements
3.1.1.4. IEC 61850 WAN engineering guidelines requirement
classification
The IEC (International Electrotechnical Commission) has published a
Technical Report which offers guidelines on how to define and deploy
Wide Area Networks for the interconnections of electric substations,
generation plants and SCADA operation centers. The IEC 61850-90-12
is providing a classification of WAN communication requirements into
4 classes. Table 8 summarizes these requirements:
Grossman Expires June 22, 2019 [Page 20]
Internet-Draft DetNet Use Cases December 2018
+----------------+------------+------------+------------+-----------+
| WAN | Class WA | Class WB | Class WC | Class WD |
| Requirement | | | | |
+----------------+------------+------------+------------+-----------+
| Application | EHV (Extra | HV (High | MV (Medium | General |
| field | High | Voltage) | Voltage) | purpose |
| | Voltage) | | | |
| Latency | 5 ms | 10 ms | 100 ms | > 100 ms |
| Jitter | 10 us | 100 us | 1 ms | 10 ms |
| Latency | 100 us | 1 ms | 10 ms | 100 ms |
| Asymetry | | | | |
| Time Accuracy | 1 us | 10 us | 100 us | 10 to 100 |
| | | | | ms |
| Bit Error rate | 10-7 to | 10-5 to | 10-3 | |
| | 10-6 | 10-4 | | |
| Unavailability | 10-7 to | 10-5 to | 10-3 | |
| | 10-6 | 10-4 | | |
| Recovery delay | Zero | 50 ms | 5 s | 50 s |
| Cyber security | extremely | High | Medium | Medium |
| | high | | | |
+----------------+------------+------------+------------+-----------+
Table 8: 61850-90-12 Communication Requirements; Courtesy of IEC
3.1.2. Generation Use Case
Energy generation systems are complex infrastructures that require
control of both the generated power and the generation
infrastructure.
3.1.2.1. Control of the Generated Power
The electrical power generation frequency must be maintained within a
very narrow band. Deviations from the acceptable frequency range are
detected and the required signals are sent to the power plants for
frequency regulation.
Automatic Generation Control (AGC) is a system for adjusting the
power output of generators at different power plants, in response to
changes in the load.
Grossman Expires June 22, 2019 [Page 21]
Internet-Draft DetNet Use Cases December 2018
+---------------------------------------------------+---------------+
| FCAG (Frequency Control Automatic Generation) | Attribute |
| Requirement | |
+---------------------------------------------------+---------------+
| One way maximum delay | 500 ms |
| Asymetric delay Required | No |
| Maximum jitter | Not critical |
| Topology | Point to |
| | point |
| Bandwidth | 20 Kbps |
| Availability | 99.999 |
| precise timing required | Yes |
| Recovery time on Node failure | N/A |
| performance management | Yes, |
| | Mandatory |
| Redundancy | Yes |
| Packet loss | 1% |
+---------------------------------------------------+---------------+
Table 9: FCAG Communication Requirements
3.1.2.2. Control of the Generation Infrastructure
The control of the generation infrastructure combines requirements
from industrial automation systems and energy generation systems.
This section considers the use case of the control of the generation
infrastructure of a wind turbine.
Grossman Expires June 22, 2019 [Page 22]
Internet-Draft DetNet Use Cases December 2018
|
|
| +-----------------+
| | +----+ |
| | |WTRM| WGEN |
WROT x==|===| | |
| | +----+ WCNV|
| |WNAC |
| +---+---WYAW---+--+
| | |
| | | +----+
|WTRF | |WMET|
| | | |
Wind Turbine | +--+-+
Controller | |
WTUR | | |
WREP | | |
WSLG | | |
WALG | WTOW | |
Figure 1: Wind Turbine Control Network
Figure 1 presents the subsystems that operate a wind turbine. These
subsystems include
o WROT (Rotor Control)
o WNAC (Nacelle Control) (nacelle: housing containing the generator)
o WTRM (Transmission Control)
o WGEN (Generator)
o WYAW (Yaw Controller) (of the tower head)
o WCNV (In-Turbine Power Converter)
o WMET (External Meteorological Station providing real time
information to the controllers of the tower)
Traffic characteristics relevant for the network planning and
dimensioning process in a wind turbine scenario are listed below.
The values in this section are based mainly on the relevant
references [Ahm14] and [Spe09]. Each logical node (Figure 1) is a
part of the metering network and produces analog measurements and
status information which must comply with their respective data rate
constraints.
Grossman Expires June 22, 2019 [Page 23]
Internet-Draft DetNet Use Cases December 2018
+-----------+--------+--------+-------------+---------+-------------+
| Subsystem | Sensor | Analog | Data Rate | Status | Data rate |
| | Count | Sample | (bytes/sec) | Sample | (bytes/sec) |
| | | Count | | Count | |
+-----------+--------+--------+-------------+---------+-------------+
| WROT | 14 | 9 | 642 | 5 | 10 |
| WTRM | 18 | 10 | 2828 | 8 | 16 |
| WGEN | 14 | 12 | 73764 | 2 | 4 |
| WCNV | 14 | 12 | 74060 | 2 | 4 |
| WTRF | 12 | 5 | 73740 | 2 | 4 |
| WNAC | 12 | 9 | 112 | 3 | 6 |
| WYAW | 7 | 8 | 220 | 4 | 8 |
| WTOW | 4 | 1 | 8 | 3 | 6 |
| WMET | 7 | 7 | 228 | - | - |
+-----------+--------+--------+-------------+---------+-------------+
Table 10: Wind Turbine Data Rate Constraints
Quality of Service (QoS) constraints for different services are
presented in Table 11. These constraints are defined by IEEE 1646
standard [IEEE1646] and IEC 61400 standard [IEC61400].
+---------------------+---------+-------------+---------------------+
| Service | Latency | Reliability | Packet Loss Rate |
+---------------------+---------+-------------+---------------------+
| Analogue measure | 16 ms | 99.99% | < 10-6 |
| Status information | 16 ms | 99.99% | < 10-6 |
| Protection traffic | 4 ms | 100.00% | < 10-9 |
| Reporting and | 1 s | 99.99% | < 10-6 |
| logging | | | |
| Video surveillance | 1 s | 99.00% | No specific |
| | | | requirement |
| Internet connection | 60 min | 99.00% | No specific |
| | | | requirement |
| Control traffic | 16 ms | 100.00% | < 10-9 |
| Data polling | 16 ms | 99.99% | < 10-6 |
+---------------------+---------+-------------+---------------------+
Table 11: Wind Turbine Reliability and Latency Constraints
3.1.2.2.1. Intra-Domain Network Considerations
A wind turbine is composed of a large set of subsystems including
sensors and actuators which require time-critical operation. The
reliability and latency constraints of these different subsystems is
shown in Table 11. These subsystems are connected to an intra-domain
network which is used to monitor and control the operation of the
turbine and connect it to the SCADA subsystems. The different
Grossman Expires June 22, 2019 [Page 24]
Internet-Draft DetNet Use Cases December 2018
components are interconnected using fiber optics, industrial buses,
industrial Ethernet, EtherCat, or a combination of them. Industrial
signaling and control protocols such as Modbus, Profibus, Profinet
and EtherCat are used directly on top of the Layer 2 transport or
encapsulated over TCP/IP.
The Data collected from the sensors and condition monitoring systems
is multiplexed onto fiber cables for transmission to the base of the
tower, and to remote control centers. The turbine controller
continuously monitors the condition of the wind turbine and collects
statistics on its operation. This controller also manages a large
number of switches, hydraulic pumps, valves, and motors within the
wind turbine.
There is usually a controller both at the bottom of the tower and in
the nacelle. The communication between these two controllers usually
takes place using fiber optics instead of copper links. Sometimes, a
third controller is installed in the hub of the rotor and manages the
pitch of the blades. That unit usually communicates with the nacelle
unit using serial communications.
3.1.2.2.2. Inter-Domain network considerations
A remote control center belonging to a grid operator regulates the
power output, enables remote actuation, and monitors the health of
one or more wind parks in tandem. It connects to the local control
center in a wind park over the Internet (Figure 2) via firewalls at
both ends. The AS path between the local control center and the Wind
Park typically involves several ISPs at different tiers. For
example, a remote control center in Denmark can regulate a wind park
in Greece over the normal public AS path between the two locations.
The remote control center is part of the SCADA system, setting the
desired power output to the wind park and reading back the result
once the new power output level has been set. Traffic between the
remote control center and the wind park typically consists of
protocols like IEC 60870-5-104 [IEC-60870-5-104], OPC XML-DA
[OPCXML], Modbus [MODBUS], and SNMP [RFC3411]. At the time of this
writing, traffic flows between the wind farm and the remote control
center are best effort. QoS requirements are not strict, so no SLAs
or service provisioning mechanisms (e.g., VPN) are employed. In case
of events like equipment failure, tolerance for alarm delay is on the
order of minutes, due to redundant systems already in place.
Grossman Expires June 22, 2019 [Page 25]
Internet-Draft DetNet Use Cases December 2018
+--------------+
| |
| |
| Wind Park #1 +----+
| | | XXXXXX
| | | X XXXXXXXX +----------------+
+--------------+ | XXXX X XXXXX | |
+---+ XXX | Remote Control |
XXX Internet +----+ Center |
+----+X XXX | |
+--------------+ | XXXXXXX XX | |
| | | XX XXXXXXX +----------------+
| | | XXXXX
| Wind Park #2 +----+
| |
| |
+--------------+
Figure 2: Wind Turbine Control via Internet
Future use cases will require bounded latency, bounded jitter and
extraordinary low packet loss for inter-domain traffic flows due to
the softwarization and virtualization of core wind farm equipment
(e.g. switches, firewalls and SCADA server components). These
factors will create opportunities for service providers to install
new services and dynamically manage them from remote locations. For
example, to enable fail-over of a local SCADA server, a SCADA server
in another wind farm site (under the administrative control of the
same operator) could be utilized temporarily (Figure 3). In that
case local traffic would be forwarded to the remote SCADA server and
existing intra-domain QoS and timing parameters would have to be met
for inter-domain traffic flows.
Grossman Expires June 22, 2019 [Page 26]
Internet-Draft DetNet Use Cases December 2018
+--------------+
| |
| |
| Wind Park #1 +----+
| | | XXXXXX
| | | X XXXXXXXX +----------------+
+--------------+ | XXXX XXXXX | |
+---+ Operator XXX | Remote Control |
XXX Administered +----+ Center |
+----+X WAN XXX | |
+--------------+ | XXXXXXX XX | |
| | | XX XXXXXXX +----------------+
| | | XXXXX
| Wind Park #2 +----+
| |
| |
+--------------+
Figure 3: Wind Turbine Control via Operator Administered WAN
3.1.3. Distribution use case
3.1.3.1. Fault Location Isolation and Service Restoration (FLISR)
Fault Location, Isolation, and Service Restoration (FLISR) refers to
the ability to automatically locate the fault, isolate the fault, and
restore service in the distribution network. This will likely be the
first widespread application of distributed intelligence in the grid.
Static power switch status (open/closed) in the network dictates the
power flow to secondary substations. Reconfiguring the network in
the event of a fault is typically done manually on site to energize/
de-energize alternate paths. Automating the operation of substation
switchgear allows the flow of power to be altered automatically under
fault conditions.
FLISR can be managed centrally from a Distribution Management System
(DMS) or executed locally through distributed control via intelligent
switches and fault sensors.
Grossman Expires June 22, 2019 [Page 27]
Internet-Draft DetNet Use Cases December 2018
+----------------------+--------------------------------------------+
| FLISR Requirement | Attribute |
+----------------------+--------------------------------------------+
| One way maximum | 80 ms |
| delay | |
| Asymetric delay | No |
| Required | |
| Maximum jitter | 40 ms |
| Topology | Point to point, point to Multi-point, |
| | Multi-point to Multi-point |
| Bandwidth | 64 Kbps |
| Availability | 99.9999 |
| precise timing | Yes |
| required | |
| Recovery time on | Depends on customer impact |
| Node failure | |
| performance | Yes, Mandatory |
| management | |
| Redundancy | Yes |
| Packet loss | 0.1% |
+----------------------+--------------------------------------------+
Table 12: FLISR Communication Requirements
3.2. Electrical Utilities Today
Many utilities still rely on complex environments formed of multiple
application-specific proprietary networks, including TDM networks.
In this kind of environment there is no mixing of OT and IT
applications on the same network, and information is siloed between
operational areas.
Specific calibration of the full chain is required, which is costly.
This kind of environment prevents utility operations from realizing
the operational efficiency benefits, visibility, and functional
integration of operational information across grid applications and
data networks.
In addition, there are many security-related issues as discussed in
the following section.
3.2.1. Security Current Practices and Limitations
Grid monitoring and control devices are already targets for cyber
attacks, and legacy telecommunications protocols have many intrinsic
network-related vulnerabilities. For example, DNP3, Modbus,
Grossman Expires June 22, 2019 [Page 28]
Internet-Draft DetNet Use Cases December 2018
PROFIBUS/PROFINET, and other protocols are designed around a common
paradigm of request and respond. Each protocol is designed for a
master device such as an HMI (Human Machine Interface) system to send
commands to subordinate slave devices to retrieve data (reading
inputs) or control (writing to outputs). Because many of these
protocols lack authentication, encryption, or other basic security
measures, they are prone to network-based attacks, allowing a
malicious actor or attacker to utilize the request-and-respond system
as a mechanism for command-and-control like functionality. Specific
security concerns common to most industrial control, including
utility telecommunication protocols include the following:
o Network or transport errors (e.g. malformed packets or excessive
latency) can cause protocol failure.
o Protocol commands may be available that are capable of forcing
slave devices into inoperable states, including powering-off
devices, forcing them into a listen-only state, disabling
alarming.
o Protocol commands may be available that are capable of restarting
communications and otherwise interrupting processes.
o Protocol commands may be available that are capable of clearing,
erasing, or resetting diagnostic information such as counters and
diagnostic registers.
o Protocol commands may be available that are capable of requesting
sensitive information about the controllers, their configurations,
or other need-to-know information.
o Most protocols are application layer protocols transported over
TCP; therefore it is easy to transport commands over non-standard
ports or inject commands into authorized traffic flows.
o Protocol commands may be available that are capable of
broadcasting messages to many devices at once (i.e. a potential
DoS).
o Protocol commands may be available to query the device network to
obtain defined points and their values (i.e. a configuration
scan).
o Protocol commands may be available that will list all available
function codes (i.e. a function scan).
These inherent vulnerabilities, along with increasing connectivity
between IT an OT networks, make network-based attacks very feasible.
Grossman Expires June 22, 2019 [Page 29]
Internet-Draft DetNet Use Cases December 2018
Simple injection of malicious protocol commands provides control over
the target process. Altering legitimate protocol traffic can also
alter information about a process and disrupt the legitimate controls
that are in place over that process. A man-in-the-middle attack
could provide both control over a process and misrepresentation of
data back to operator consoles.
3.3. Electrical Utilities Future
The business and technology trends that are sweeping the utility
industry will drastically transform the utility business from the way
it has been for many decades. At the core of many of these changes
is a drive to modernize the electrical grid with an integrated
telecommunications infrastructure. However, interoperability
concerns, legacy networks, disparate tools, and stringent security
requirements all add complexity to the grid transformation. Given
the range and diversity of the requirements that should be addressed
by the next generation telecommunications infrastructure, utilities
need to adopt a holistic architectural approach to integrate the
electrical grid with digital telecommunications across the entire
power delivery chain.
The key to modernizing grid telecommunications is to provide a
common, adaptable, multi-service network infrastructure for the
entire utility organization. Such a network serves as the platform
for current capabilities while enabling future expansion of the
network to accommodate new applications and services.
To meet this diverse set of requirements, both today and in the
future, the next generation utility telecommunnications network will
be based on open-standards-based IP architecture. An end-to-end IP
architecture takes advantage of nearly three decades of IP technology
development, facilitating interoperability and device management
across disparate networks and devices, as it has been already
demonstrated in many mission-critical and highly secure networks.
IPv6 is seen as a future telecommunications technology for the Smart
Grid; the IEC (International Electrotechnical Commission) and
different National Committees have mandated a specific adhoc group
(AHG8) to define the migration strategy to IPv6 for all the IEC TC57
power automation standards. The AHG8 has finalised the work on the
migration strategy and the following Technical Report has been
issued: IEC TR 62357-200:2015: Guidelines for migration from Internet
Protocol version 4 (IPv4) to Internet Protocol version 6 (IPv6).
Cloud-based SCADA systems will control and monitor the critical and
non-critical subsystems of generation systems, for example wind
farms.
Grossman Expires June 22, 2019 [Page 30]
Internet-Draft DetNet Use Cases December 2018
3.3.1. Migration to Packet-Switched Network
Throughout the world, utilities are increasingly planning for a
future based on smart grid applications requiring advanced
telecommunications systems. Many of these applications utilize
packet connectivity for communicating information and control signals
across the utility's Wide Area Network (WAN), made possible by
technologies such as multiprotocol label switching (MPLS). The data
that traverses the utility WAN includes:
o Grid monitoring, control, and protection data
o Non-control grid data (e.g. asset data for condition-based
monitoring)
o Physical safety and security data (e.g. voice and video)
o Remote worker access to corporate applications (voice, maps,
schematics, etc.)
o Field area network backhaul for smart metering, and distribution
grid management
o Enterprise traffic (email, collaboration tools, business
applications)
WANs support this wide variety of traffic to and from substations,
the transmission and distribution grid, generation sites, between
control centers, and between work locations and data centers. To
maintain this rapidly expanding set of applications, many utilities
are taking steps to evolve present time-division multiplexing (TDM)
based and frame relay infrastructures to packet systems. Packet-
based networks are designed to provide greater functionalities and
higher levels of service for applications, while continuing to
deliver reliability and deterministic (real-time) traffic support.
3.3.2. Telecommunications Trends
These general telecommunications topics are in addition to the use
cases that have been addressed so far. These include both current
and future telecommunications related topics that should be factored
into the network architecture and design.
3.3.2.1. General Telecommunications Requirements
o IP Connectivity everywhere
o Monitoring services everywhere and from different remote centers
Grossman Expires June 22, 2019 [Page 31]
Internet-Draft DetNet Use Cases December 2018
o Move services to a virtual data center
o Unify access to applications / information from the corporate
network
o Unify services
o Unified Communications Solutions
o Mix of fiber and microwave technologies - obsolescence of SONET/
SDH or TDM
o Standardize grid telecommunications protocol to opened standard to
ensure interoperability
o Reliable Telecommunications for Transmission and Distribution
Substations
o IEEE 1588 time synchronization Client / Server Capabilities
o Integration of Multicast Design
o QoS Requirements Mapping
o Enable Future Network Expansion
o Substation Network Resilience
o Fast Convergence Design
o Scalable Headend Design
o Define Service Level Agreements (SLA) and Enable SLA Monitoring
o Integration of 3G/4G Technologies and future technologies
o Ethernet Connectivity for Station Bus Architecture
o Ethernet Connectivity for Process Bus Architecture
o Protection, teleprotection and PMU (Phaser Measurement Unit) on IP
3.3.2.2. Specific Network topologies of Smart Grid Applications
Utilities often have very large private telecommunications networks.
It covers an entire territory / country. The main purpose of the
network, until now, has been to support transmission network
monitoring, control, and automation, remote control of generation
Grossman Expires June 22, 2019 [Page 32]
Internet-Draft DetNet Use Cases December 2018
sites, and providing FCAPS (Fault, Configuration, Accounting,
Performance, Security) services from centralized network operation
centers.
Going forward, one network will support operation and maintenance of
electrical networks (generation, transmission, and distribution),
voice and data services for ten of thousands of employees and for
exchange with neighboring interconnections, and administrative
services. To meet those requirements, utility may deploy several
physical networks leveraging different technologies across the
country: an optical network and a microwave network for instance.
Each protection and automatism system between two points has two
telecommunications circuits, one on each network. Path diversity
between two substations is key. Regardless of the event type
(hurricane, ice storm, etc.), one path needs to stay available so the
system can still operate.
In the optical network, signals are transmitted over more than tens
of thousands of circuits using fiber optic links, microwave and
telephone cables. This network is the nervous system of the
utility's power transmission operations. The optical network
represents ten of thousands of km of cable deployed along the power
lines, with individual runs as long as 280 km.
3.3.2.3. Precision Time Protocol
Some utilities do not use GPS clocks in generation substations. One
of the main reasons is that some of the generation plants are 30 to
50 meters deep under ground and the GPS signal can be weak and
unreliable. Instead, atomic clocks are used. Clocks are
synchronized amongst each other. Rubidium clocks provide clock and
1ms timestamps for IRIG-B.
Some companies plan to transition to the Precision Time Protocol
(PTP, [IEEE1588]), distributing the synchronization signal over the
IP/MPLS network. PTP provides a mechanism for synchronizing the
clocks of participating nodes to a high degree of accuracy and
precision.
PTP operates based on the following assumptions:
It is assumed that the network eliminates cyclic forwarding of PTP
messages within each communication path (e.g. by using a spanning
tree protocol).
PTP is tolerant of an occasional missed message, duplicated
message, or message that arrived out of order. However, PTP
assumes that such impairments are relatively rare.
Grossman Expires June 22, 2019 [Page 33]
Internet-Draft DetNet Use Cases December 2018
PTP was designed assuming a multicast communication model, however
PTP also supports a unicast communication model as long as the
behavior of the protocol is preserved.
Like all message-based time transfer protocols, PTP time accuracy
is degraded by delay asymmetry in the paths taken by event
messages. Asymmetry is not detectable by PTP, however, if such
delays are known a priori, PTP can correct for asymmetry.
IEC 61850 defines the use of IEC/IEEE 61850-9-3:2016. The title is:
Precision time protocol profile for power utility automation. It is
based on Annex B/IEC 62439 which offers the support of redundant
attachment of clocks to Parallel Redundancy Protocol (PRP) and High-
availability Seamless Redundancy (HSR) networks.
3.3.3. Security Trends in Utility Networks
Although advanced telecommunications networks can assist in
transforming the energy industry by playing a critical role in
maintaining high levels of reliability, performance, and
manageability, they also introduce the need for an integrated
security infrastructure. Many of the technologies being deployed to
support smart grid projects such as smart meters and sensors can
increase the vulnerability of the grid to attack. Top security
concerns for utilities migrating to an intelligent smart grid
telecommunications platform center on the following trends:
o Integration of distributed energy resources
o Proliferation of digital devices to enable management, automation,
protection, and control
o Regulatory mandates to comply with standards for critical
infrastructure protection
o Migration to new systems for outage management, distribution
automation, condition-based maintenance, load forecasting, and
smart metering
o Demand for new levels of customer service and energy management
This development of a diverse set of networks to support the
integration of microgrids, open-access energy competition, and the
use of network-controlled devices is driving the need for a converged
security infrastructure for all participants in the smart grid,
including utilities, energy service providers, large commercial and
industrial, as well as residential customers. Securing the assets of
electric power delivery systems (from the control center to the
Grossman Expires June 22, 2019 [Page 34]
Internet-Draft DetNet Use Cases December 2018
substation, to the feeders and down to customer meters) requires an
end-to-end security infrastructure that protects the myriad of
telecommunications assets used to operate, monitor, and control power
flow and measurement.
"Cyber security" refers to all the security issues in automation and
telecommunications that affect any functions related to the operation
of the electric power systems. Specifically, it involves the
concepts of:
o Integrity : data cannot be altered undetectably
o Authenticity (data origin authentication): the telecommunications
parties involved must be validated as genuine
o Authorization : only requests and commands from the authorized
users can be accepted by the system
o Confidentiality : data must not be accessible to any
unauthenticated users
When designing and deploying new smart grid devices and
telecommunications systems, it is imperative to understand the
various impacts of these new components under a variety of attack
situations on the power grid. Consequences of a cyber attack on the
grid telecommunications network can be catastrophic. This is why
security for smart grid is not just an ad hoc feature or product,
it's a complete framework integrating both physical and Cyber
security requirements and covering the entire smart grid networks
from generation to distribution. Security has therefore become one
of the main foundations of the utility telecom network architecture
and must be considered at every layer with a defense-in-depth
approach. Migrating to IP based protocols is key to address these
challenges for two reasons:
o IP enables a rich set of features and capabilities to enhance the
security posture
o IP is based on open standards, which allows interoperability
between different vendors and products, driving down the costs
associated with implementing security solutions in OT networks.
Securing OT (Operation technology) telecommunications over packet-
switched IP networks follow the same principles that are foundational
for securing the IT infrastructure, i.e., consideration must be given
to enforcing electronic access control for both person-to-machine and
machine-to-machine communications, and providing the appropriate
Grossman Expires June 22, 2019 [Page 35]
Internet-Draft DetNet Use Cases December 2018
levels of data privacy, device and platform integrity, and threat
detection and mitigation.
3.4. Electrical Utilities Asks
o Mixed L2 and L3 topologies
o Deterministic behavior
o Bounded latency and jitter
o Tight feedback intervals
o High availability, low recovery time
o Redundancy, low packet loss
o Precise timing
o Centralized computing of deterministic paths
o Distributed configuration may also be useful
4. Building Automation Systems
4.1. Use Case Description
A Building Automation System (BAS) manages equipment and sensors in a
building for improving residents' comfort, reducing energy
consumption, and responding to failures and emergencies. For
example, the BAS measures the temperature of a room using sensors and
then controls the HVAC (heating, ventilating, and air conditioning)
to maintain a set temperature and minimize energy consumption.
A BAS primarily performs the following functions:
o Periodically measures states of devices, for example humidity and
illuminance of rooms, open/close state of doors, FAN speed, etc.
o Stores the measured data.
o Provides the measured data to BAS systems and operators.
o Generates alarms for abnormal state of devices.
o Controls devices (e.g. turn off room lights at 10:00 PM).
Grossman Expires June 22, 2019 [Page 36]
Internet-Draft DetNet Use Cases December 2018
4.2. Building Automation Systems Today
4.2.1. BAS Architecture
A typical BAS architecture of today is shown in Figure 4.
+----------------------------+
| |
| BMS HMI |
| | | |
| +----------------------+ |
| | Management Network | |
| +----------------------+ |
| | | |
| LC LC |
| | | |
| +----------------------+ |
| | Field Network | |
| +----------------------+ |
| | | | | |
| Dev Dev Dev Dev |
| |
+----------------------------+
BMS := Building Management Server
HMI := Human Machine Interface
LC := Local Controller
Figure 4: BAS architecture
There are typically two layers of network in a BAS. The upper one is
called the Management Network and the lower one is called the Field
Network. In management networks an IP-based communication protocol
is used, while in field networks non-IP based communication protocols
("field protocols") are mainly used. Field networks have specific
timing requirements, whereas management networks can be best-effort.
A Human Machine Interface (HMI) is typically a desktop PC used by
operators to monitor and display device states, send device control
commands to Local Controllers (LCs), and configure building schedules
(for example "turn off all room lights in the building at 10:00 PM").
A Building Management Server (BMS) performs the following operations.
o Collect and store device states from LCs at regular intervals.
o Send control values to LCs according to a building schedule.
Grossman Expires June 22, 2019 [Page 37]
Internet-Draft DetNet Use Cases December 2018
o Send an alarm signal to operators if it detects abnormal devices
states.
The BMS and HMI communicate with LCs via IP-based "management
protocols" (see standards [bacnetip], [knx]).
A LC is typically a Programmable Logic Controller (PLC) which is
connected to several tens or hundreds of devices using "field
protocols". An LC performs the following kinds of operations:
o Measure device states and provide the information to BMS or HMI.
o Send control values to devices, unilaterally or as part of a
feedback control loop.
There are many field protocols used at the time of this writing; some
are standards-based and others are proprietary (see standards
[lontalk], [modbus], [profibus] and [flnet]). The result is that
BASs have multiple MAC/PHY modules and interfaces. This makes BASs
more expensive, slower to develop, and can result in "vendor lock-in"
with multiple types of management applications.
4.2.2. BAS Deployment Model
An example BAS for medium or large buildings is shown in Figure 5.
The physical layout spans multiple floors, and there is a monitoring
room where the BAS management entities are located. Each floor will
have one or more LCs depending upon the number of devices connected
to the field network.
Grossman Expires June 22, 2019 [Page 38]
Internet-Draft DetNet Use Cases December 2018
+--------------------------------------------------+
| Floor 3 |
| +----LC~~~~+~~~~~+~~~~~+ |
| | | | | |
| | Dev Dev Dev |
| | |
|--- | ------------------------------------------|
| | Floor 2 |
| +----LC~~~~+~~~~~+~~~~~+ Field Network |
| | | | | |
| | Dev Dev Dev |
| | |
|--- | ------------------------------------------|
| | Floor 1 |
| +----LC~~~~+~~~~~+~~~~~+ +-----------------|
| | | | | | Monitoring Room |
| | Dev Dev Dev | |
| | | BMS HMI |
| | Management Network | | | |
| +--------------------------------+-----+ |
| | |
+--------------------------------------------------+
Figure 5: BAS Deployment model for Medium/Large Buildings
Each LC is connected to the monitoring room via the Management
network, and the management functions are performed within the
building. In most cases, fast Ethernet (e.g. 100BASE-T) is used for
the management network. Since the management network is non-
realtime, use of Ethernet without quality of service is sufficient
for today's deployment.
In the field network a variety of physical interfaces such as RS232C
and RS485 are used, which have specific timing requirements. Thus if
a field network is to be replaced with an Ethernet or wireless
network, such networks must support time-critical deterministic
flows.
In Figure 6, another deployment model is presented in which the
management system is hosted remotely. This is becoming popular for
small office and residential buildings in which a standalone
monitoring system is not cost-effective.
Grossman Expires June 22, 2019 [Page 39]
Internet-Draft DetNet Use Cases December 2018
+---------------+
| Remote Center |
| |
| BMS HMI |
+------------------------------------+ | | | |
| Floor 2 | | +---+---+ |
| +----LC~~~~+~~~~~+ Field Network| | | |
| | | | | | Router |
| | Dev Dev | +-------|-------+
| | | |
|--- | ------------------------------| |
| | Floor 1 | |
| +----LC~~~~+~~~~~+ | |
| | | | | |
| | Dev Dev | |
| | | |
| | Management Network | WAN |
| +------------------------Router-------------+
| |
+------------------------------------+
Figure 6: Deployment model for Small Buildings
Some interoperability is possible today in the Management Network,
but not in today's field networks due to their non-IP-based design.
4.2.3. Use Cases for Field Networks
Below are use cases for Environmental Monitoring, Fire Detection, and
Feedback Control, and their implications for field network
performance.
4.2.3.1. Environmental Monitoring
The BMS polls each LC at a maximum measurement interval of 100ms (for
example to draw a historical chart of 1 second granularity with a 10x
sampling interval) and then performs the operations as specified by
the operator. Each LC needs to measure each of its several hundred
sensors once per measurement interval. Latency is not critical in
this scenario as long as all sensor values are completed in the
measurement interval. Availability is expected to be 99.999 %.
4.2.3.2. Fire Detection
On detection of a fire, the BMS must stop the HVAC, close the fire
shutters, turn on the fire sprinklers, send an alarm, etc. There are
typically ~10s of sensors per LC that BMS needs to manage. In this
Grossman Expires June 22, 2019 [Page 40]
Internet-Draft DetNet Use Cases December 2018
scenario the measurement interval is 10-50ms, the communication delay
is 10ms, and the availability must be 99.9999 %.
4.2.3.3. Feedback Control
BAS systems utilize feedback control in various ways; the most time-
critial is control of DC motors, which require a short feedback
interval (1-5ms) with low communication delay (10ms) and jitter
(1ms). The feedback interval depends on the characteristics of the
device and a target quality of control value. There are typically
~10s of such devices per LC.
Communication delay is expected to be less than 10ms, jitter less
than 1ms while the availability must be 99.9999% .
4.2.4. Security Considerations
When BAS field networks were developed it was assumed that the field
networks would always be physically isolated from external networks
and therefore security was not a concern. In today's world many BASs
are managed remotely and are thus connected to shared IP networks and
so security is definitely a concern, yet security features are not
available in the majority of BAS field network deployments .
The management network, being an IP-based network, has the protocols
available to enable network security, but in practice many BAS
systems do not implement even the available security features such as
device authentication or encryption for data in transit.
4.3. BAS Future
In the future more fine-grained environmental monitoring and lower
energy consumption will emerge which will require more sensors and
devices, thus requiring larger and more complex building networks.
Building networks will be connected to or converged with other
networks (Enterprise network, Home network, and Internet).
Therefore better facilities for network management, control,
reliability and security are critical in order to improve resident
and operator convenience and comfort. For example the ability to
monitor and control building devices via the internet would enable
(for example) control of room lights or HVAC from a resident's
desktop PC or phone application.
Grossman Expires June 22, 2019 [Page 41]
Internet-Draft DetNet Use Cases December 2018
4.4. BAS Asks
The community would like to see an interoperable protocol
specification that can satisfy the timing, security, availability and
QoS constraints described above, such that the resulting converged
network can replace the disparate field networks. Ideally this
connectivity could extend to the open Internet.
This would imply an architecture that can guarantee
o Low communication delays (from <10ms to 100ms in a network of
several hundred devices)
o Low jitter (< 1 ms)
o Tight feedback intervals (1ms - 10ms)
o High network availability (up to 99.9999% )
o Availability of network data in disaster scenario
o Authentication between management and field devices (both local
and remote)
o Integrity and data origin authentication of communication data
between field and management devices
o Confidentiality of data when communicated to a remote device
5. Wireless for Industrial Applications
5.1. Use Case Description
Wireless networks are useful for industrial applications, for example
when portable, fast-moving or rotating objects are involved, and for
the resource-constrained devices found in the Internet of Things
(IoT).
Such network-connected sensors, actuators, control loops (etc.)
typically require that the underlying network support real-time
quality of service (QoS), as well as specific classes of other
network properties such as reliability, redundancy, and security.
These networks may also contain very large numbers of devices, for
example for factories, "big data" acquisition, and the IoT. Given
the large numbers of devices installed, and the potential
pervasiveness of the IoT, this is a huge and very cost-sensitive
Grossman Expires June 22, 2019 [Page 42]
Internet-Draft DetNet Use Cases December 2018
market such that small cost reductions can save large amounts of
money.
5.1.1. Network Convergence using 6TiSCH
Some wireless network technologies support real-time QoS, and are
thus useful for these kinds of networks, but others do not.
This use case focuses on one specific wireless network technology
which provides the required deterministic QoS, which is "IPv6 over
the TSCH mode of IEEE 802.15.4e" (6TiSCH, where TSCH stands for
"Time-Slotted Channel Hopping", see [I-D.ietf-6tisch-architecture],
[IEEE802154], [IEEE802154e], and [RFC7554]).
There are other deterministic wireless busses and networks available
today, however they are imcompatible with each other, and
incompatible with IP traffic (for example [ISA100], [WirelessHART]).
Thus the primary goal of this use case is to apply 6TiSCH as a
converged IP- and standards-based wireless network for industrial
applications, i.e. to replace multiple proprietary and/or
incompatible wireless networking and wireless network management
standards.
5.1.2. Common Protocol Development for 6TiSCH
Today there are a number of protocols required by 6TiSCH which are
still in development, and a second intent of this use case is to
highlight the ways in which these "missing" protocols share goals in
common with DetNet. Thus it is possible that some of the protocol
technology developed for DetNet will also be applicable to 6TiSCH.
These protocol goals are identified here, along with their
relationship to DetNet. It is likely that ultimately the resulting
protocols will not be identical, but will share design principles
which contribute to the eficiency of enabling both DetNet and 6TiSCH.
One such commonality is that although at a different time scale, in
both TSN [IEEE802.1TSNTG] and TSCH a packet crosses the network from
node to node follows a precise schedule, as a train that leaves
intermediate stations at precise times along its path. This kind of
operation reduces collisions, saves energy, and enables engineering
the network for deterministic properties.
Another commonality is remote monitoring and scheduling management of
a TSCH network by a Path Computation Element (PCE) and Network
Management Entity (NME). The PCE/NME manage timeslots and device
resources in a manner that minimizes the interaction with and the
Grossman Expires June 22, 2019 [Page 43]
Internet-Draft DetNet Use Cases December 2018
load placed on resource-constrained devices. For example, a tiny IoT
device may have just enough buffers to store one or a few IPv6
packets, and will have limited bandwidth between peers such that it
can maintain only a small amount of peer information, and will not be
able to store many packets waiting to be forwarded. It is
advantageous then for it to only be required to carry out the
specific behavior assigned to it by the PCE/NME (as opposed to
maintaining its own IP stack, for example).
It is possible that there will be some peer-to-peer communication,
for example the PCE may communicate only indirectly with some devices
in order to enable hierarchical configuration of the system.
6TiSCH depends on [PCE] and [I-D.ietf-detnet-architecture].
6TiSCH also depends on the fact that DetNet will maintain consistency
with [IEEE802.1TSNTG].
5.2. Wireless Industrial Today
Today industrial wireless is accomplished using multiple
deterministic wireless networks which are incompatible with each
other and with IP traffic.
6TiSCH is not yet fully specified, so it cannot be used in today's
applications.
5.3. Wireless Industrial Future
5.3.1. Unified Wireless Network and Management
DetNet and 6TiSCH together can enable converged transport of
deterministic and best-effort traffic flows between real-time
industrial devices and wide area networks via IP routing. A high
level view of a basic such network is shown in Figure 7.
Grossman Expires June 22, 2019 [Page 44]
Internet-Draft DetNet Use Cases December 2018
---+-------- ............ ------------
| External Network |
| +-----+
+-----+ | NME |
| | LLN Border | |
| | router +-----+
+-----+
o o o
o o o o
o o LLN o o o
o o o o
o
Figure 7: Basic 6TiSCH Network
Figure 8 shows a backbone router federating multiple synchronized
6TiSCH subnets into a single subnet connected to the external
network.
---+-------- ............ ------------
| External Network |
| +-----+
| +-----+ | NME |
+-----+ | +-----+ | |
| | Router | | PCE | +-----+
| | +--| |
+-----+ +-----+
| |
| Subnet Backbone |
+--------------------+------------------+
| | |
+-----+ +-----+ +-----+
| | Backbone | | Backbone | | Backbone
o | | router | | router | | router
+-----+ +-----+ +-----+
o o o o o
o o o o o o o o o o o
o o o LLN o o o o
o o o o o o o o o o o o
Figure 8: Extended 6TiSCH Network
The backbone router must ensure end-to-end deterministic behavior
between the LLN and the backbone. This should be accomplished in
conformance with the work done in [I-D.ietf-detnet-architecture] with
respect to Layer-3 aspects of deterministic networks that span
multiple Layer-2 domains.
Grossman Expires June 22, 2019 [Page 45]
Internet-Draft DetNet Use Cases December 2018
The PCE must compute a deterministic path end-to-end across the TSCH
network and IEEE802.1 TSN Ethernet backbone, and DetNet protocols are
expected to enable end-to-end deterministic forwarding.
+-----+
| IoT |
| G/W |
+-----+
^ <---- Elimination
| |
Track branch | |
+-------+ +--------+ Subnet Backbone
| |
+--|--+ +--|--+
| | | Backbone | | | Backbone
o | | | router | | | router
+--/--+ +--|--+
o / o o---o----/ o
o o---o--/ o o o o o
o \ / o o LLN o
o v <---- Replication
o
Figure 9: 6TiSCH Network with PRE
5.3.1.1. PCE and 6TiSCH ARQ Retries
6TiSCH uses the IEEE802.15.4 Automatic Repeat-reQuest (ARQ) mechanism
to provide higher reliability of packet delivery. ARQ is related to
packet replication and elimination because there are two independent
paths for packets to arrive at the destination, and if an expected
packed does not arrive on one path then it checks for the packet on
the second path.
Although to date this mechanism is only used by wireless networks,
this may be a technique that would be appropriate for DetNet and so
aspects of the enabling protocol could be co-developed.
For example, in Figure 9, a Track is laid out from a field device in
a 6TiSCH network to an IoT gateway that is located on a IEEE802.1 TSN
backbone.
In ARQ the Replication function in the field device sends a copy of
each packet over two different branches, and the PCE schedules each
hop of both branches so that the two copies arrive in due time at the
gateway. In case of a loss on one branch, hopefully the other copy
Grossman Expires June 22, 2019 [Page 46]
Internet-Draft DetNet Use Cases December 2018
of the packet still arrives within the allocated time. If two copies
make it to the IoT gateway, the Elimination function in the gateway
ignores the extra packet and presents only one copy to upper layers.
At each 6TiSCH hop along the Track, the PCE may schedule more than
one timeSlot for a packet, so as to support Layer-2 retries (ARQ).
In deployments at the time of this writing, a TSCH Track does not
necessarily support PRE but is systematically multi-path. This means
that a Track is scheduled so as to ensure that each hop has at least
two forwarding solutions, and the forwarding decision is to try the
preferred one and use the other in case of Layer-2 transmission
failure as detected by ARQ.
5.3.2. Schedule Management by a PCE
A common feature of 6TiSCH and DetNet is the action of a PCE to
configure paths through the network. Specifically, what is needed is
a protocol and data model that the PCE will use to get/set the
relevant configuration from/to the devices, as well as perform
operations on the devices. This protocol should be developed by
DetNet with consideration for its reuse by 6TiSCH. The remainder of
this section provides a bit more context from the 6TiSCH side.
5.3.2.1. PCE Commands and 6TiSCH CoAP Requests
The 6TiSCH device does not expect to place the request for bandwidth
between itself and another device in the network. Rather, an
operation control system invoked through a human interface specifies
the required traffic specification and the end nodes (in terms of
latency and reliability). Based on this information, the PCE must
compute a path between the end nodes and provision the network with
per-flow state that describes the per-hop operation for a given
packet, the corresponding timeslots, and the flow identification that
enables recognizing that a certain packet belongs to a certain path,
etc.
For a static configuration that serves a certain purpose for a long
period of time, it is expected that a node will be provisioned in one
shot with a full schedule, which incorporates the aggregation of its
behavior for multiple paths. 6TiSCH expects that the programing of
the schedule will be done over COAP as discussed in
[I-D.ietf-6tisch-coap].
6TiSCH expects that the PCE commands will be mapped back and forth
into CoAP by a gateway function at the edge of the 6TiSCH network.
For instance, it is possible that a mapping entity on the backbone
transforms a non-CoAP protocol such as PCEP into the RESTful
Grossman Expires June 22, 2019 [Page 47]
Internet-Draft DetNet Use Cases December 2018
interfaces that the 6TiSCH devices support. This architecture will
be refined to comply with DetNet [I-D.ietf-detnet-architecture] when
the work is formalized. Related information about 6TiSCH can be
found at [I-D.ietf-6tisch-6top-interface] and RPL [RFC6550].
A protocol may be used to update the state in the devices during
runtime, for example if it appears that a path through the network
has ceased to perform as expected, but in 6TiSCH that flow was not
designed and no protocol was selected. DetNet should define the
appropriate end-to-end protocols to be used in that case. The
implication is that these state updates take place once the system is
configured and running, i.e. they are not limited to the initial
communication of the configuration of the system.
A "slotFrame" is the base object that a PCE would manipulate to
program a schedule into an LLN node ([I-D.ietf-6tisch-architecture]).
The PCE should read energy data from devices and compute paths that
will implement policies on how energy in devices is consumed, for
instance to ensure that the spent energy does not exceeded the
available energy over a period of time. Note: this statement implies
that an extensible protocol for communicating device info to the PCE
and enabling the PCE to act on it will be part of the DetNet
architecture, however for subnets with specific protocols (e.g.
CoAP) a gateway may be required.
6TiSCH devices can discover their neighbors over the radio using a
mechanism such as beacons, but even though the neighbor information
is available in the 6TiSCH interface data model, 6TiSCH does not
describe a protocol to proactively push the neighborhood information
to a PCE. DetNet should define such a protocol; one possible design
alternative is that it could operate over CoAP, alternatively it
could be converted to/from CoAP by a gateway. Such a protocol could
carry multiple metrics, for example similar to those used for RPL
operations [RFC6551]
5.3.2.2. 6TiSCH IP Interface
"6top" ([I-D.wang-6tisch-6top-sublayer]) is a logical link control
sitting between the IP layer and the TSCH MAC layer which provides
the link abstraction that is required for IP operations. The 6top
data model and management interfaces are further discussed in
[I-D.ietf-6tisch-6top-interface] and [I-D.ietf-6tisch-coap].
An IP packet that is sent along a 6TiSCH path uses the Differentiated
Services Per-Hop-Behavior Group called Deterministic Forwarding, as
described in [I-D.svshah-tsvwg-deterministic-forwarding].
Grossman Expires June 22, 2019 [Page 48]
Internet-Draft DetNet Use Cases December 2018
5.3.3. 6TiSCH Security Considerations
On top of the classical requirements for protection of control
signaling, it must be noted that 6TiSCH networks operate on limited
resources that can be depleted rapidly in a DoS attack on the system,
for instance by placing a rogue device in the network, or by
obtaining management control and setting up unexpected additional
paths.
5.4. Wireless Industrial Asks
6TiSCH depends on DetNet to define:
o Configuration (state) and operations for deterministic paths
o End-to-end protocols for deterministic forwarding (tagging, IP)
o Protocol for packet replication and elimination
6. Cellular Radio
6.1. Use Case Description
This use case describes the application of deterministic networking
in the context of cellular telecom transport networks. Important
elements include time synchronization, clock distribution, and ways
of establishing time-sensitive streams for both Layer-2 and Layer-3
user plane traffic.
6.1.1. Network Architecture
Figure 10 illustrates a 3GPP-defined cellular network architecture
typical at the time of this writing, which includes "Fronthaul",
"Midhaul" and "Backhaul" network segments. The "Fronthaul" is the
network connecting base stations (baseband processing units) to the
remote radio heads (antennas). The "Midhaul" is the network inter-
connecting base stations (or small cell sites). The "Backhaul" is
the network or links connecting the radio base station sites to the
network controller/gateway sites (i.e. the core of the 3GPP cellular
network).
In Figure 10 "eNB" ("E-UTRAN Node B") is the hardware that is
connected to the mobile phone network which communicates directly
with mobile handsets ([TS36300]).
Grossman Expires June 22, 2019 [Page 49]
Internet-Draft DetNet Use Cases December 2018
Y (remote radio heads (antennas))
\
Y__ \.--. .--. +------+
\_( `. +---+ _(Back`. | 3GPP |
Y------( Front )----|eNB|----( Haul )----| core |
( ` .Haul ) +---+ ( ` . ) ) | netw |
/`--(___.-' \ `--(___.-' +------+
Y_/ / \.--. \
Y_/ _( Mid`. \
( Haul ) \
( ` . ) ) \
`--(___.-'\_____+---+ (small cell sites)
\ |SCe|__Y
+---+ +---+
Y__|eNB|__Y
+---+
Y_/ \_Y ("local" radios)
Figure 10: Generic 3GPP-based Cellular Network Architecture
6.1.2. Delay Constraints
The available processing time for Fronthaul networking overhead is
limited to the available time after the baseband processing of the
radio frame has completed. For example in Long Term Evolution (LTE)
radio, processing of a radio frame is allocated 3ms but typically the
processing uses most of it, allowing only a small fraction to be used
by the Fronthaul network (e.g. up to 250us one-way delay, though the
existing spec ([NGMN-fronth]) supports delay only up to 100us). This
ultimately determines the distance the remote radio heads can be
located from the base stations (e.g., 100us equals roughly 20 km of
optical fiber-based transport). Allocation options of the available
time budget between processing and transport are under heavy
discussions in the mobile industry.
For packet-based transport the allocated transport time (e.g. CPRI
would allow for 100us delay [CPRI]) is consumed by all nodes and
buffering between the remote radio head and the baseband processing
unit, plus the distance-incurred delay.
The baseband processing time and the available "delay budget" for the
fronthaul is likely to change in the forthcoming "5G" due to reduced
radio round trip times and other architectural and service
requirements [NGMN].
The transport time budget, as noted above, places limitations on the
distance that remote radio heads can be located from base stations
(i.e. the link length). In the above analysis, the entire transport
Grossman Expires June 22, 2019 [Page 50]
Internet-Draft DetNet Use Cases December 2018
time budget is assumed to be available for link propagation delay.
However the transport time budget can be broken down into three
components: scheduling /queueing delay, transmission delay, and link
propagation delay. Using today's Fronthaul networking technology,
the queuing, scheduling and transmission components might become the
dominant factors in the total transport time rather than the link
propagation delay. This is especially true in cases where the
Fronthaul link is relatively short and it is shared among multiple
Fronthaul flows, for example in indoor and small cell networks,
massive MIMO antenna networks, and split Fronthaul architectures.
DetNet technology can improve this application by controlling and
reducing the time required for the queuing, scheduling and
transmission operations by properly assigning the network resources,
thus leaving more of the transport time budget available for link
propagation, and thus enabling longer link lengths. However, link
length is usually a given parameter and is not a controllable network
parameter, since RRH and BBU sights are usually located in
predetermined locations. However, the number of antennas in an RRH
sight might increase for example by adding more antennas, increasing
the MIMO capability of the network or support of massive MIMO. This
means increasing the number of the fronthaul flows sharing the same
fronthaul link. DetNet can now control the bandwidth assignment of
the fronthaul link and the scheduling of fronthaul packets over this
link and provide adequate buffer provisioning for each flow to reduce
the packet loss rate.
Another way in which DetNet technology can aid Fronthaul networks is
by providing effective isolation from best-effort (and other classes
of) traffic, which can arise as a result of network slicing in 5G
networks where Fronthaul traffic generated in different network
slices might have differing performance requirements. DetNet
technology can also dynamically control the bandwidth assignment,
scheduling and packet forwarding decisions and the buffer
provisioning of the Fronthaul flows to guarantee the end-to-end delay
of the Fronthaul packets and minimize the packet loss rate.
[METIS] documents the fundamental challenges as well as overall
technical goals of the future 5G mobile and wireless system as the
starting point. These future systems should support much higher data
volumes and rates and significantly lower end-to-end latency for 100x
more connected devices (at similar cost and energy consumption levels
as today's system).
For Midhaul connections, delay constraints are driven by Inter-Site
radio functions like Coordinated Multipoint Processing (CoMP, see
[CoMP]). CoMP reception and transmission is a framework in which
multiple geographically distributed antenna nodes cooperate to
Grossman Expires June 22, 2019 [Page 51]
Internet-Draft DetNet Use Cases December 2018
improve the performance of the users served in the common cooperation
area. The design principal of CoMP is to extend single-cell to
multi-UE (User Equipment) transmission to a multi-cell-to-multi-UEs
transmission by base station cooperation.
CoMP has delay-sensitive performance parameters, which are "midhaul
latency" and "CSI (Channel State Information) reporting and
accuracy". The essential feature of CoMP is signaling between eNBs,
so Midhaul latency is the dominating limitation of CoMP performance.
Generally, CoMP can benefit from coordinated scheduling (either
distributed or centralized) of different cells if the signaling delay
between eNBs is within 1-10ms. This delay requirement is both rigid
and absolute because any uncertainty in delay will degrade the
performance significantly.
Inter-site CoMP is one of the key requirements for 5G and is also a
goal for 4.5G network architecture.
6.1.3. Time Synchronization Constraints
Fronthaul time synchronization requirements are given by [TS25104],
[TS36104], [TS36211], and [TS36133]. These can be summarized for the
3GPP LTE-based networks as:
Delay Accuracy:
+-8ns (i.e. +-1/32 Tc, where Tc is the UMTS Chip time of 1/3.84
MHz) resulting in a round trip accuracy of +-16ns. The value is
this low to meet the 3GPP Timing Alignment Error (TAE) measurement
requirements. Note: performance guarantees of low nanosecond
values such as these are considered to be below the DetNet layer -
it is assumed that the underlying implementation, e.g. the
hardware, will provide sufficient support (e.g. buffering) to
enable this level of accuracy. These values are maintained in the
use case to give an indication of the overall application.
Timing Alignment Error:
Timing Alignment Error (TAE) is problematic to Fronthaul networks
and must be minimized. If the transport network cannot guarantee
low enough TAE then additional buffering has to be introduced at
the edges of the network to buffer out the jitter. Buffering is
not desirable as it reduces the total available delay budget.
Packet Delay Variation (PDV) requirements can be derived from TAE
for packet based Fronthaul networks.
Grossman Expires June 22, 2019 [Page 52]
Internet-Draft DetNet Use Cases December 2018
* For multiple input multiple output (MIMO) or TX diversity
transmissions, at each carrier frequency, TAE shall not exceed
65 ns (i.e. 1/4 Tc).
* For intra-band contiguous carrier aggregation, with or without
MIMO or TX diversity, TAE shall not exceed 130 ns (i.e. 1/2
Tc).
* For intra-band non-contiguous carrier aggregation, with or
without MIMO or TX diversity, TAE shall not exceed 260 ns (i.e.
one Tc).
* For inter-band carrier aggregation, with or without MIMO or TX
diversity, TAE shall not exceed 260 ns.
Transport link contribution to radio frequency error:
+-2 PPB. This value is considered to be "available" for the
Fronthaul link out of the total 50 PPB budget reserved for the
radio interface. Note: the reason that the transport link
contributes to radio frequency error is as follows. At the time
of this writing, Fronthaul communication is from the radio unit to
remote radio head directly. The remote radio head is essentially
a passive device (without buffering etc.) The transport drives
the antenna directly by feeding it with samples and everything the
transport adds will be introduced to radio as-is. So if the
transport causes additional frequency error that shows immediately
on the radio as well. Note: performance guarantees of low
nanosecond values such as these are considered to be below the
DetNet layer - it is assumed that the underlying implementation,
e.g. the hardware, will provide sufficient support to enable this
level of performance. These values are maintained in the use case
to give an indication of the overall application.
The above listed time synchronization requirements are difficult to
meet with point-to-point connected networks, and more difficult when
the network includes multiple hops. It is expected that networks
must include buffering at the ends of the connections as imposed by
the jitter requirements, since trying to meet the jitter requirements
in every intermediate node is likely to be too costly. However,
every measure to reduce jitter and delay on the path makes it easier
to meet the end-to-end requirements.
In order to meet the timing requirements both senders and receivers
must remain time synchronized, demanding very accurate clock
distribution, for example support for IEEE 1588 transparent clocks or
boundary clocks in every intermediate node.
Grossman Expires June 22, 2019 [Page 53]
Internet-Draft DetNet Use Cases December 2018
In cellular networks from the LTE radio era onward, phase
synchronization is needed in addition to frequency synchronization
([TS36300], [TS23401]). Time constraints are also important due to
their impact on packet loss. If a packet is delivered too late, then
the packet may be dropped by the host.
6.1.4. Transport Loss Constraints
Fronthaul and Midhaul networks assume almost error-free transport.
Errors can result in a reset of the radio interfaces, which can cause
reduced throughput or broken radio connectivity for mobile customers.
For packetized Fronthaul and Midhaul connections packet loss may be
caused by BER, congestion, or network failure scenarios. Different
fronthaul functional splits are being considered by 3GPP, requiring
strict frame loss ratio (FLR) guarantees. As one example (referring
to the legacy CPRI split which is option 8 in 3GPP) lower layers
splits may imply an FLR of less than 10E-7 for data traffic and less
than 10E-6 for control and management traffic.
Many of the tools available for eliminating packet loss for Fronthaul
and Midhaul networks have serious challenges, for example
retransmitting lost packets and/or using forward error correction
(FEC) to circumvent bit errors is practically impossible due to the
additional delay incurred. Using redundant streams for better
guarantees for delivery is also practically impossible in many cases
due to high bandwidth requirements of Fronthaul and Midhaul networks.
Protection switching is also a candidate but at the time of this
writing, available technologies for the path switch are too slow to
avoid reset of mobile interfaces.
Fronthaul links are assumed to be symmetric, and all Fronthaul
streams (i.e. those carrying radio data) have equal priority and
cannot delay or pre-empt each other. This implies that the network
must guarantee that each time-sensitive flow meets their schedule.
6.1.5. Security Considerations
Establishing time-sensitive streams in the network entails reserving
networking resources for long periods of time. It is important that
these reservation requests be authenticated to prevent malicious
reservation attempts from hostile nodes (or accidental
misconfiguration). This is particularly important in the case where
the reservation requests span administrative domains. Furthermore,
the reservation information itself should be digitally signed to
reduce the risk of a legitimate node pushing a stale or hostile
configuration into another networking node.
Grossman Expires June 22, 2019 [Page 54]
Internet-Draft DetNet Use Cases December 2018
Note: This is considered important for the security policy of the
network, but does not affect the core DetNet architecture and design.
6.2. Cellular Radio Networks Today
6.2.1. Fronthaul
Today's Fronthaul networks typically consist of:
o Dedicated point-to-point fiber connection is common
o Proprietary protocols and framings
o Custom equipment and no real networking
At the time of this writing, solutions for Fronthaul are direct
optical cables or Wavelength-Division Multiplexing (WDM) connections.
6.2.2. Midhaul and Backhaul
Today's Midhaul and Backhaul networks typically consist of:
o Mostly normal IP networks, MPLS-TP, etc.
o Clock distribution and sync using 1588 and SyncE
Telecommunication networks in the Mid- and Backhaul are already
heading towards transport networks where precise time synchronization
support is one of the basic building blocks. While the transport
networks themselves have practically transitioned to all-IP packet-
based networks to meet the bandwidth and cost requirements, highly
accurate clock distribution has become a challenge.
In the past, Mid- and Backhaul connections were typically based on
Time Division Multiplexing (TDM-based) and provided frequency
synchronization capabilities as a part of the transport media.
Alternatively other technologies such as Global Positioning System
(GPS) or Synchronous Ethernet (SyncE) are used [SyncE].
Both Ethernet and IP/MPLS [RFC3031] (and PseudoWires (PWE) [RFC3985]
for legacy transport support) have become popular tools to build and
manage new all-IP Radio Access Networks (RANs)
[I-D.kh-spring-ip-ran-use-case]. Although various timing and
synchronization optimizations have already been proposed and
implemented including 1588 PTP enhancements
[I-D.ietf-tictoc-1588overmpls] and [RFC8169], these solution are not
necessarily sufficient for the forthcoming RAN architectures nor do
Grossman Expires June 22, 2019 [Page 55]
Internet-Draft DetNet Use Cases December 2018
they guarantee the more stringent time-synchronization requirements
such as [CPRI].
There are also existing solutions for TDM over IP such as [RFC4553],
[RFC5086], and [RFC5087], as well as TDM over Ethernet transports
such as [MEF8].
6.3. Cellular Radio Networks Future
Future Cellular Radio Networks will be based on a mix of different
xHaul networks (xHaul = front-, mid- and backhaul), and future
transport networks should be able to support all of them
simultaneously. It is already envisioned today that:
o Not all "cellular radio network" traffic will be IP, for example
some will remain at Layer 2 (e.g. Ethernet based). DetNet
solutions must address all traffic types (Layer 2, Layer 3) with
the same tools and allow their transport simultaneously.
o All forms of xHaul networks will need some form of DetNet
solutions. For example with the advent of 5G some Backhaul
traffic will also have DetNet requirements, for example traffic
belonging to time-critical 5G applications.
o Different splits of the functionality run on the base stations and
the on-site units could co-exist on the same Fronthaul and
Backhaul network.
Future Cellular Radio networks should contain the following:
o Unified standards-based transport protocols and standard
networking equipment that can make use of underlying deterministic
link-layer services
o Unified and standards-based network management systems and
protocols in all parts of the network (including Fronthaul)
New radio access network deployment models and architectures may
require time- sensitive networking services with strict requirements
on other parts of the network that previously were not considered to
be packetized at all. Time and synchronization support are already
topical for Backhaul and Midhaul packet networks [MEF22.1.1] and are
becoming a real issue for Fronthaul networks also. Specifically in
Fronthaul networks the timing and synchronization requirements can be
extreme for packet based technologies, for example, on the order of
sub +-20 ns packet delay variation (PDV) and frequency accuracy of
+0.002 PPM [Fronthaul].
Grossman Expires June 22, 2019 [Page 56]
Internet-Draft DetNet Use Cases December 2018
The actual transport protocols and/or solutions to establish required
transport "circuits" (pinned-down paths) for Fronthaul traffic are
still undefined. Those are likely to include (but are not limited
to) solutions directly over Ethernet, over IP, and using MPLS/
PseudoWire transport.
Interesting and important work for time-sensitive networking has been
done for Ethernet [TSNTG], which specifies the use of IEEE 1588 time
precision protocol (PTP) [IEEE1588] in the context of IEEE 802.1D and
IEEE 802.1Q. [IEEE8021AS] specifies a Layer 2 time synchronizing
service, and other specifications such as IEEE 1722 [IEEE1722]
specify Ethernet-based Layer-2 transport for time-sensitive streams.
However even these Ethernet TSN features may not be sufficient for
Fronthaul traffic. Therefore, having specific profiles that take the
requirements of Fronthaul into account is desirable [IEEE8021CM].
New promising work seeks to enable the transport of time-sensitive
fronthaul streams in Ethernet bridged networks [IEEE8021CM].
Analogous to IEEE 1722 there is an ongoing standardization effort to
define the Layer-2 transport encapsulation format for transporting
radio over Ethernet (RoE) in the IEEE 1904.3 Task Force [IEEE19143].
As mentioned in Section 6.1.2, 5G communications will provide one of
the most challenging cases for delay sensitive networking. In order
to meet the challenges of ultra-low latency and ultra-high
throughput, 3GPP has studied various "functional splits" for 5G,
i.e., physical decomposition of the gNodeB base station and
deployment of its functional blocks in different locations [TR38801].
These splits are numbered from split option 1 (Dual Connectivity, a
split in which the radio resource control is centralized and other
radio stack layers are in distributed units) to split option 8 (a
PHY-RF split in which RF functionality is in a distributed unit and
the rest of the radio stack is in the centralized unit), with each
intermediate split having its own data rate and delay requirements.
Packetized versions of different splits have been proposed including
eCPRI [eCPRI] and RoE (as previously noted). Both provide Ethernet
encapsulations, and eCPRI is also capable of IP encapsulation.
All-IP RANs and xHaul networks would benefit from time
synchronization and time-sensitive transport services. Although
Ethernet appears to be the unifying technology for the transport,
there is still a disconnect providing Layer 3 services. The protocol
stack typically has a number of layers below the Ethernet Layer 2
that shows up to the Layer 3 IP transport. It is not uncommon that
on top of the lowest layer (optical) transport there is the first
layer of Ethernet followed one or more layers of MPLS, PseudoWires
Grossman Expires June 22, 2019 [Page 57]
Internet-Draft DetNet Use Cases December 2018
and/or other tunneling protocols finally carrying the Ethernet layer
visible to the user plane IP traffic.
While there are existing technologies to establish circuits through
the routed and switched networks (especially in MPLS/PWE space),
there is still no way to signal the time synchronization and time-
sensitive stream requirements/reservations for Layer-3 flows in a way
that addresses the entire transport stack, including the Ethernet
layers that need to be configured.
Furthermore, not all "user plane" traffic will be IP. Therefore, the
same solution also must address the use cases where the user plane
traffic is a different layer, for example Ethernet frames.
There is existing work describing the problem statement
[I-D.ietf-detnet-problem-statement] and the architecture
[I-D.ietf-detnet-architecture] for deterministic networking (DetNet)
that targets solutions for time-sensitive (IP/transport) streams with
deterministic properties over Ethernet-based switched networks.
6.4. Cellular Radio Networks Asks
A standard for data plane transport specification which is:
o Unified among all xHauls (meaning that different flows with
diverse DetNet requirements can coexist in the same network and
traverse the same nodes without interfering with each other)
o Deployed in a highly deterministic network environment
o Capable of supporting multiple functional splits simultaneously,
including existing Backhaul and CPRI Fronthaul and potentially new
modes as defined for example in 3GPP; these goals can be supported
by the existing DetNet Use Case Common Themes, notably "Mix of
Deterministic and Best-Effort Traffic", "Bounded Latency", "Low
Latency", "Symmetrical Path Delays", and "Deterministic Flows".
o Capable of supporting Network Slicing and Multi-tenancy; these
goals can be supported by the same DetNet themes noted above.
o Capable of transporting both in-band and out-band control traffic
(OAM info, ...).
o Deployable over multiple data link technologies (e.g., IEEE 802.3,
mmWave, etc.).
A standard for data flow information models that are:
Grossman Expires June 22, 2019 [Page 58]
Internet-Draft DetNet Use Cases December 2018
o Aware of the time sensitivity and constraints of the target
networking environment
o Aware of underlying deterministic networking services (e.g., on
the Ethernet layer)
7. Industrial Machine to Machine (M2M)
7.1. Use Case Description
Industrial Automation in general refers to automation of
manufacturing, quality control and material processing. This
"machine to machine" (M2M) use case considers machine units in a
plant floor which periodically exchange data with upstream or
downstream machine modules and/or a supervisory controller within a
local area network.
The actors of M2M communication are Programmable Logic Controllers
(PLCs). Communication between PLCs and between PLCs and the
supervisory PLC (S-PLC) is achieved via critical control/data streams
Figure 11.
S (Sensor)
\ +-----+
PLC__ \.--. .--. ---| MES |
\_( `. _( `./ +-----+
A------( Local )-------------( L2 )
( Net ) ( Net ) +-------+
/`--(___.-' `--(___.-' ----| S-PLC |
S_/ / PLC .--. / +-------+
A_/ \_( `.
(Actuator) ( Local )
( Net )
/`--(___.-'\
/ \ A
S A
Figure 11: Current Generic Industrial M2M Network Architecture
This use case focuses on PLC-related communications; communication to
Manufacturing-Execution-Systems (MESs) are not addressed.
This use case covers only critical control/data streams; non-critical
traffic between industrial automation applications (such as
communication of state, configuration, set-up, and database
communication) are adequately served by prioritizing techniques
available at the time of this writing. Such traffic can use up to
Grossman Expires June 22, 2019 [Page 59]
Internet-Draft DetNet Use Cases December 2018
80% of the total bandwidth required. There is also a subset of non-
time-critical traffic that must be reliable even though it is not
time-sensitive.
In this use case the primary need for deterministic networking is to
provide end-to-end delivery of M2M messages within specific timing
constraints, for example in closed loop automation control. Today
this level of determinism is provided by proprietary networking
technologies. In addition, standard networking technologies are used
to connect the local network to remote industrial automation sites,
e.g. over an enterprise or metro network which also carries other
types of traffic. Therefore, flows that should be forwarded with
deterministic guarantees need to be sustained regardless of the
amount of other flows in those networks.
7.2. Industrial M2M Communication Today
Today, proprietary networks fulfill the needed timing and
availability for M2M networks.
The network topologies used today by industrial automation are
similar to those used by telecom networks: Daisy Chain, Ring, Hub and
Spoke, and Comb (a subset of Daisy Chain).
PLC-related control/data streams are transmitted periodically and
carry either a pre-configured payload or a payload configured during
runtime.
Some industrial applications require time synchronization at the end
nodes. For such time-coordinated PLCs, accuracy of 1 microsecond is
required. Even in the case of "non-time-coordinated" PLCs time sync
may be needed e.g. for timestamping of sensor data.
Industrial network scenarios require advanced security solutions. At
the time of this writing, many industrial production networks are
physically separated. Preventing critical flows from being leaked
outside a domain is handled by filtering policies that are typically
enforced in firewalls.
7.2.1. Transport Parameters
The Cycle Time defines the frequency of message(s) between industrial
actors. The Cycle Time is application dependent, in the range of 1ms
- 100ms for critical control/data streams.
Because industrial applications assume deterministic transport for
critical Control-Data-Stream parameters (instead of defining latency
and delay variation parameters) it is sufficient to fulfill the upper
Grossman Expires June 22, 2019 [Page 60]
Internet-Draft DetNet Use Cases December 2018
bound of latency (maximum latency). The underlying networking
infrastructure must ensure a maximum end-to-end delivery time of
messages in the range of 100 microseconds to 50 milliseconds
depending on the control loop application.
The bandwidth requirements of control/data streams are usually
calculated directly from the bytes-per-cycle parameter of the control
loop. For PLC-to-PLC communication one can expect 2 - 32 streams
with packet size in the range of 100 - 700 bytes. For S-PLC to PLCs
the number of streams is higher - up to 256 streams. Usually no more
than 20% of available bandwidth is used for critical control/data
streams. In today's networks 1Gbps links are commonly used.
Most PLC control loops are rather tolerant of packet loss, however
critical control/data streams accept no more than 1 packet loss per
consecutive communication cycle (i.e. if a packet gets lost in cycle
"n", then the next cycle ("n+1") must be lossless). After two or
more consecutive packet losses the network may be considered to be
"down" by the Application.
As network downtime may impact the whole production system the
required network availability is rather high (99.999%).
Based on the above parameters some form of redundancy will be
required for M2M communications, however any individual solution
depends on several parameters including cycle time, delivery time,
etc.
7.2.2. Stream Creation and Destruction
In an industrial environment, critical control/data streams are
created rather infrequently, on the order of ~10 times per day / week
/ month. Most of these critical control/data streams get created at
machine startup, however flexibility is also needed during runtime,
for example when adding or removing a machine. Going forward as
production systems become more flexible, there will be a significant
increase in the rate at which streams are created, changed and
destroyed.
7.3. Industrial M2M Future
We foresee a converged IP-standards-based network with deterministic
properties that can satisfy the timing, security and reliability
constraints described above. Today's proprietary networks could then
be interfaced to such a network via gateways or, in the case of new
installations, devices could be connected directly to the converged
network.
Grossman Expires June 22, 2019 [Page 61]
Internet-Draft DetNet Use Cases December 2018
For this use case time synchronization accuracy on the order of 1us
is expected.
7.4. Industrial M2M Asks
o Converged IP-based network
o Deterministic behavior (bounded latency and jitter )
o High availability (presumably through redundancy) (99.999 %)
o Low message delivery time (100us - 50ms)
o Low packet loss (with bounded number of consecutive lost packets)
o Security (e.g. prevent critical flows from being leaked between
physically separated networks)
8. Mining Industry
8.1. Use Case Description
The mining industry is highly dependent on networks to monitor and
control their systems both in open-pit and underground extraction,
transport and refining processes. In order to reduce risks and
increase operational efficiency in mining operations, a number of
processes have migrated the operators from the extraction site to
remote control and monitoring.
In the case of open pit mining, autonomous trucks are used to
transport the raw materials from the open pit to the refining factory
where the final product (e.g. Copper) is obtained. Although the
operation is autonomous, the tracks are remotely monitored from a
central facility.
In pit mines, the monitoring of the tailings or mine dumps is
critical in order to minimize environmental pollution. In the past,
monitoring has been conducted through manual inspection of pre-
installed dataloggers. Cabling is not usually exploited in such
scenarios due to the cost and complex deployment requirements. At
the time of this writing, wireless technologies are being employed to
monitor these cases permanently. Slopes are also monitored in order
to anticipate possible mine collapse. Due to the unstable terrain,
cable maintenance is costly and complex and hence wireless
technologies are employed.
In the underground monitoring case, autonomous vehicles with
extraction tools travel autonomously through the tunnels, but their
Grossman Expires June 22, 2019 [Page 62]
Internet-Draft DetNet Use Cases December 2018
operational tasks (such as excavation, stone breaking and transport)
are controlled remotely from a central facility. This generates
video and feedback upstream traffic plus downstream actuator control
traffic.
8.2. Mining Industry Today
At the time of this writing, the mining industry uses a packet
switched architecture supported by high speed ethernet. However in
order to achieve the delay and packet loss requirements the network
bandwidth is overestimated, thus providing very low efficiency in
terms of resource usage.
QoS is implemented at the Routers to separate video, management,
monitoring and process control traffic for each stream.
Since mobility is involved in this process, the connection between
the backbone and the mobile devices (e.g. trucks, trains and
excavators) is solved using a wireless link. These links are based
on 802.11 for open-pit mining and "leaky feeder" communications for
underground mining. (A "leaky feeder" communication system consists
of a coaxial cable run along tunnels which emits and receives radio
waves, functioning as an extended antenna. The cable is "leaky" in
that it has gaps or slots in its outer conductor to allow the radio
signal to leak into or out of the cable along its entire length.)
Lately in pit mines the use of LPWAN technologies has been extended:
Tailings, slopes and mine dumps are monitored by battery-powered
dataloggers that make use of robust long range radio technologies.
Reliability is usually ensured through retransmissions at L2.
Gateways or concentrators act as bridges forwarding the data to the
backbone ethernet network. Deterministic requirements are biased
towards reliability rather than latency as events are slowly
triggered or can be anticipated in advance.
At the mineral processing stage, conveyor belts and refining
processes are controlled by a SCADA system, which provides the in-
factory delay-constrained networking requirements.
At the time of this writing, voice communications are served by a
redundant trunking infrastructure, independent from data networks.
8.3. Mining Industry Future
Mining operations and management are converging towards a combination
of autonomous operation and teleoperation of transport and extraction
machines. This means that video, audio, monitoring and process
Grossman Expires June 22, 2019 [Page 63]
Internet-Draft DetNet Use Cases December 2018
control traffic will increase dramatically. Ideally, all activities
on the mine will rely on network infrastructure.
Wireless for open-pit mining is already a reality with LPWAN
technologies and it is expected to evolve to more advanced LPWAN
technologies such as those based on LTE to increase last hop
reliability or novel LPWAN flavours with deterministic access.
One area in which DetNet can improve this use case is in the wired
networks that make up the "backbone network" of the system, which
connect together many wireless access points (APs). The mobile
machines (which are connected to the network via wireless) transition
from one AP to the next as they move about. A deterministic,
reliable, low latency backbone can enable these transitions to be
more reliable.
Connections which extend all the way from the base stations to the
machinery via a mix of wired and wireless hops would also be
beneficial, for example to improve remote control responsiveness of
digging machines. However to guarantee deterministic performance of
a DetNet, the end-to-end underlying network must be deterministic.
Thus for this use case if a deterministic wireless transport is
integrated with a wire-based DetNet network, it could create the
desired wired plus wireless end-to-end deterministic network.
8.4. Mining Industry Asks
o Improved bandwidth efficiency
o Very low delay to enable machine teleoperation
o Dedicated bandwidth usage for high resolution video streams
o Predictable delay to enable realtime monitoring
o Potential to construct a unified DetNet network over a combination
of wired and deterministic wireless links
9. Private Blockchain
9.1. Use Case Description
Blockchain was created with bitcoin as a 'public' blockchain on the
open Internet, however blockchain has also spread far beyond its
original host into various industries such as smart manufacturing,
logistics, security, legal rights and others. In these industries
blockchain runs in designated and carefully managed networks in which
Grossman Expires June 22, 2019 [Page 64]
Internet-Draft DetNet Use Cases December 2018
deterministic networking requirements could be addressed by DetNet.
Such implementations are referred to as 'private' blockchain.
The sole distinction between public and private blockchain is defined
by who is allowed to participate in the network, execute the
consensus protocol, and maintain the shared ledger.
Today's networks treat the traffic from blockchain on a best-effort
basis, but blockchain operation could be made much more efficient if
deterministic networking services were available to minimize latency
and packet loss in the network.
9.1.1. Blockchain Operation
A 'block' runs as a container of a batch of primary items such as
transactions, property records etc. The blocks are chained in such a
way that the hash of the previous block works as the pointer to the
header of the new block. Confirmation of each block requires a
consensus mechanism. When an item arrives at a blockchain node, the
latter broadcasts this item to the rest of the nodes which receive
and verify it and put it in the ongoing block. The block
confirmation process begins as the number of items reaches the
predefined block capacity, at which time the node broadcasts its
proved block to the rest of the nodes, to be verified and chained.
The result is that block N+1 of each chain transitively vouches for
blocks N and before of that chain.
9.1.2. Blockchain Network Architecture
Blockchain node communication and coordination is achieved mainly
through frequent point-to-multi-point communication, however
persistent point-to-point connections are used to transport both the
items and the blocks to the other nodes. For example, consider the
following implementation.
When a node is initiated, it first requests the other nodes' address
from a specific entity such as DNS, then it creates persistent
connections each of with other nodes. If a node confirms an item, it
sends the item to the other nodes via these persistent connections.
As a new block in a node is completed and is proven by the
surrounding nodes, it propagates towards its neighbor nodes. When
node A receives a block, it verifies it, then sends an invite message
to its neighbor B. Neighbor B checks to see if the designated block
is available, and responds to A if it is unavailable, then A sends
the complete block to B. B repeats the process (as done by A above)
to start the next round of block propagation.
Grossman Expires June 22, 2019 [Page 65]
Internet-Draft DetNet Use Cases December 2018
The challenge of blockchain network operation is not overall data
rates, since the volume from both block and item stays between
hundreds of bytes to a couple of megabytes per second, but is in
transporting the blocks with minimum latency to maximize efficiency
of the blockchain consensus process. The efficiency of differing
implementations of the consensus process may be affected to a
differing degree by the latency (and variation of latency) of the
network.
9.1.3. Security Considerations
Security is crucial to blockchain applications, and at the time of
this writing, blockchain systems address security issues mainly at
the application level, where cryptography as well as hash-based
consensus play a leading role in preventing both double-spending and
malicious service attacks. However, there is concern that in the
proposed use case of a private blockchain network which is dependent
on deterministic properties, the network could be vulnerable to
delays and other specific attacks against determinism which could
interrupt service.
9.2. Private Blockchain Today
Today private blockchain runs in L2 or L3 VPN, in general without
guaranteed determinism. The industry players are starting to realize
that improving determinism in their blockchain networks could improve
the performance of their service, but as of today these goals are not
being met.
9.3. Private Blockchain Future
Blockchain system performance can be greatly improved through
deterministic networking service primarily because it would
accelerate the consensus process. It would be valuable to be able to
design a private blockchain network with the following properties:
o Transport of point-to-multi-point traffic in a coordinated network
architecture rather than at the application layer (which typically
uses point-to-point connections)
o Guaranteed transport latency
o Reduced packet loss (to the point where packet retransmission-
incurred delay would be negligible.)
Grossman Expires June 22, 2019 [Page 66]
Internet-Draft DetNet Use Cases December 2018
9.4. Private Blockchain Asks
o Layer 2 and Layer 3 multicast of blockchain traffic
o Item and block delivery with bounded, low latency and negligible
packet loss
o Coexistence in a single network of blockchain and IT traffic.
o Ability to scale the network by distributing the centralized
control of the network across multiple control entities.
10. Network Slicing
10.1. Use Case Description
Network Slicing divides one physical network infrastructure into
multiple logical networks. Each slice, corresponding to a logical
network, uses resources and network functions independently from each
other. Network Slicing provides flexibility of resource allocation
and service quality customization.
Future services will demand network performance with a wide variety
of characteristics such as high data rate, low latency, low loss
rate, security and many other parameters. Ideally every service
would have its own physical network satisfying its particular
performance requirements, however that would be prohibitively
expensive. Network Slicing can provide a customized slice for a
single service, and multiple slices can share the same physical
network. This method can optimize the performance for the service at
lower cost, and the flexibility of setting up and release the slices
also allows the user to allocate the network resources dynamically.
Unlike the other use cases presented here, Network Slicing is not a
specific application that depends on specific deterministic
properties; rather it is introduced as an area of networking to which
DetNet might be applicable.
10.2. DetNet Applied to Network Slicing
10.2.1. Resource Isolation Across Slices
One of the requirements discussed for Network Slicing is the "hard"
separation of various users' deterministic performance. That is, it
should be impossible for activity, lack of activity, or changes in
activity of one or more users to have any appreciable effect on the
deterministic performance parameters of any other slices. Typical
techniques used today, which share a physical network among users, do
Grossman Expires June 22, 2019 [Page 67]
Internet-Draft DetNet Use Cases December 2018
not offer this level of isolation. DetNet can supply point-to-point
or point-to-multipoint paths that offer bandwidth and latency
guarantees to a user that cannot be affected by other users' data
traffic. Thus DetNet is a powerful tool when latency and reliability
are required in Network Slicing.
10.2.2. Deterministic Services Within Slices
Slices may need to provide services with DetNet-type performance
guarantees, however note that a system can be implemented to provide
such services in more than one way. For example the slice itself
might be implemented using DetNet, and thus the slice can provide
service guarantees and isolation to its users without any particular
DetNet awareness on the part of the users' applications.
Alternatively, a "non-DetNet-aware" slice may host an application
that itself implements DetNet services and thus can enjoy similar
service guarantees.
10.3. A Network Slicing Use Case Example - 5G Bearer Network
Network Slicing is a core feature of 5G defined in 3GPP, which is
under development at the time of this writing [TR38501]. A network
slice in a mobile network is a complete logical network including
Radio Access Network (RAN) and Core Network (CN). It provides
telecommunication services and network capabilities, which may vary
from slice to slice. A 5G bearer network is a typical use case of
Network Slicing; for example consider three 5G service scenarios:
eMMB, URLLC, and mMTC.
o eMBB (Enhanced Mobile Broadband) focuses on services characterized
by high data rates, such as high definition videos, virtual
reality, augmented reality, and fixed mobile convergence.
o URLLC (Ultra-Reliable and Low Latency Communications) focuses on
latency-sensitive services, such as self-driving vehicles, remote
surgery, or drone control.
o mMTC (massive Machine Type Communications) focuses on services
that have high requirements for connection density, such as those
typical for smart city and smart agriculture use cases.
A 5G bearer network could use DetNet to provide hard resource
isolation across slices and within the slice. For example consider
Slice-A and Slice-B, with DetNet used to transit services URLLC-A and
URLLC-B over them. Without DetNet, URLLC-A and URLLC-B would compete
for bandwidth resource, and latency and reliability would not be
guaranteed. With DetNet, URLLC-A and URLLC-B have separate bandwidth
Grossman Expires June 22, 2019 [Page 68]
Internet-Draft DetNet Use Cases December 2018
reservation and there is no resource conflict between them, as though
they were in different logical networks.
10.4. Non-5G Applications of Network Slicing
Although operation of services not related to 5G is not part of the
5G Network Slicing definition and scope, Network Slicing is likely to
become a preferred approach to providing various services across a
shared physical infrastructure. Examples include providing
electrical utilities services and pro audio services via slices. Use
cases like these could become more common once the work for the 5G
core network evolves to include wired as well as wireless access.
10.5. Limitations of DetNet in Network Slicing
DetNet cannot cover every Network Slicing use case. One issue is
that DetNet is a point-to-point or point-to-multipoint technology,
however Network Slicing ultimately needs multi-point to multi-point
guarantees. Another issue is that the number of flows that can be
carried by DetNet is limited by DetNet scalability; flow aggregation
and queuing management modification may help address this.
Additional work and discussion are needed to address these topics.
10.6. Network Slicing Today and Future
Network Slicing has the promise to satisfy many requirements of
future network deployment scenarios, but it is still a collection of
ideas and analysis, without a specific technical solution. DetNet is
one of various technologies that have potential to be used in Network
Slicing, along with for example Flex-E and Segment Routing. For more
information please see the IETF99 Network Slicing BOF session agenda
and materials.
10.7. Network Slicing Asks
o Isolation from other flows through Queuing Management
o Service Quality Customization and Guarantee
o Security
11. Use Case Common Themes
This section summarizes the expected properties of a DetNet network,
based on the use cases as described in this draft.
Grossman Expires June 22, 2019 [Page 69]
Internet-Draft DetNet Use Cases December 2018
11.1. Unified, standards-based network
11.1.1. Extensions to Ethernet
A DetNet network is not "a new kind of network" - it based on
extensions to existing Ethernet standards, including elements of IEEE
802.1 AVB/TSN and related standards. Presumably it will be possible
to run DetNet over other underlying transports besides Ethernet, but
Ethernet is explicitly supported.
11.1.2. Centrally Administered
In general a DetNet network is not expected to be "plug and play" -
it is expected that there is some centralized network configuration
and control system. Such a system may be in a single central
location, or it maybe distributed across multiple control entities
that function together as a unified control system for the network.
However, the ability to "hot swap" components (e.g. due to
malfunction) is similar enough to "plug and play" that this kind of
behavior may be expected in DetNet networks, depending on the
implementation.
11.1.3. Standardized Data Flow Information Models
Data Flow Information Models to be used with DetNet networks are to
be specified by DetNet.
11.1.4. L2 and L3 Integration
A DetNet network is intended to integrate between Layer 2 (bridged)
network(s) (e.g. AVB/TSN LAN) and Layer 3 (routed) network(s) (e.g.
using IP-based protocols). One example of this is "making AVB/TSN-
type deterministic performance available from Layer 3 applications,
e.g. using RTP". Another example is "connecting two AVB/TSN LANs
("islands") together through a standard router".
11.1.5. Consideration for IPv4
This Use Cases draft explicitly does not specify any particular
implementation or protocol, however it has been observed that various
of the use cases described (and their associated industries) are
explicitly based on IPv4 (as opposed to IPv6) and it is not
considered practical to expect them to migrate to IPv6 in order to
use DetNet. Thus the expectation is that even if not every feature
of DetNet is available in an IPv4 context, at least some of the
significant benefits (such as guaranteed end-to-end delivery and low
latency) are expected to be available.
Grossman Expires June 22, 2019 [Page 70]
Internet-Draft DetNet Use Cases December 2018
11.1.6. Guaranteed End-to-End Delivery
Packets in a DetNet flow are guaranteed not to be dropped by the
network due to congestion. However, the network may drop packets for
intended reasons, e.g. per security measures. Similarly best-effort
traffic on a DetNet is subject to being dropped (as on a non-DetNet
IP network). Also note that this guarantee applies to the actions of
DetNet protocol software, and does not provide any guarantee against
lower level errors such as media errors or checksum errors.
11.1.7. Replacement for Multiple Proprietary Deterministic Networks
There are many proprietary non-interoperable deterministic Ethernet-
based networks available; DetNet is intended to provide an open-
standards-based alternative to such networks.
11.1.8. Mix of Deterministic and Best-Effort Traffic
DetNet is intended to support coexistance of time-sensitive
operational (OT) traffic and information (IT) traffic on the same
("unified") network.
11.1.9. Unused Reserved BW to be Available to Best-Effort Traffic
If bandwidth reservations are made for a stream but the associated
bandwidth is not used at any point in time, that bandwidth is made
available on the network for best-effort traffic. If the owner of
the reserved stream then starts transmitting again, the bandwidth is
no longer available for best-effort traffic, on a moment-to-moment
basis. Note that such "temporarily available" bandwidth is not
available for time-sensitive traffic, which must have its own
reservation.
11.1.10. Lower Cost, Multi-Vendor Solutions
The DetNet network specifications are intended to enable an ecosystem
in which multiple vendors can create interoperable products, thus
promoting device diversity and potentially higher numbers of each
device manufactured, promoting cost reduction and cost competition
among vendors. The intent is that DetNet networks should be able to
be created at lower cost and with greater diversity of available
devices than existing proprietary networks.
11.2. Scalable Size
DetNet networks range in size from very small, e.g. inside a single
industrial machine, to very large, for example a Utility Grid network
spanning a whole country, and involving many "hops" over various
Grossman Expires June 22, 2019 [Page 71]
Internet-Draft DetNet Use Cases December 2018
kinds of links for example radio repeaters, microwave linkes, fiber
optic links, etc.. However recall that the scope of DetNet is
confined to networks that are centrally administered, and explicitly
excludes unbounded decentralized networks such as the Internet.
11.2.1. Scalable Number of Flows
The number of flows in a given network application can potentially be
large, and can potentially grow faster than the number of nodes and
hops. So the network should provide a sufficient (perhaps
configurable) maximum number of flows for any given application.
11.3. Scalable Timing Parameters and Accuracy
11.3.1. Bounded Latency
The DetNet Data Flow Information Model is expected to provide means
to configure the network that include parameters for querying network
path latency, requesting bounded latency for a given stream,
requesting worst case maximum and/or minimum latency for a given path
or stream, and so on. It is an expected case that the network may
not be able to provide a given requested service level, and if so the
network control system should reply that the requested services is
not available (as opposed to accepting the parameter but then not
delivering the desired behavior).
11.3.2. Low Latency
Applications may require "extremely low latency" however depending on
the application these may mean very different latency values; for
example "low latency" across a Utility grid network is on a different
time scale than "low latency" in a motor control loop in a small
machine. The intent is that the mechanisms for specifying desired
latency include wide ranges, and that architecturally there is
nothing to prevent arbirtrarily low latencies from being implemented
in a given network.
11.3.3. Bounded Jitter (Latency Variation)
As with the other Latency-related elements noted above, parameters
should be available to determine or request the allowed variation in
latency.
11.3.4. Symmetrical Path Delays
Some applications would like to specify that the transit delay time
values be equal for both the transmit and return paths.
Grossman Expires June 22, 2019 [Page 72]
Internet-Draft DetNet Use Cases December 2018
11.4. High Reliability and Availability
Reliablity is of critical importance to many DetNet applications, in
which consequences of failure can be extraordinarily high in terms of
cost and even human life. DetNet based systems are expected to be
implemented with essentially arbitrarily high availability (for
example 99.9999% up time, or even 12 nines). The intent is that the
DetNet designs should not make any assumptions about the level of
reliability and availability that may be required of a given system,
and should define parameters for communicating these kinds of metrics
within the network.
A strategy used by DetNet for providing such extraordinarily high
levels of reliability is to provide redundant paths that can be
seamlessly switched between, while maintaining the required
performance of that system.
11.5. Security
Security is of critical importance to many DetNet applications. A
DetNet network must be able to be made secure against devices
failures, attackers, misbehaving devices, and so on. In a DetNet
network the data traffic is expected to be be time-sensitive, thus in
addition to arriving with the data content as intended, the data must
also arrive at the expected time. This may present "new" security
challenges to implementers, and must be addressed accordingly. There
are other security implications, including (but not limited to) the
change in attack surface presented by packet replication and
elimination.
11.6. Deterministic Flows
Reserved bandwidth data flows must be isolated from each other and
from best-effort traffic, so that even if the network is saturated
with best-effort (and/or reserved bandwidth) traffic, the configured
flows are not adversely affected.
12. Security Considerations
This document covers a number of representative applications and
network scenarios that are expected to make use of DetNet
technologies. Each of the potential DetNet uses cases will have
security considerations from both the use-specific and DetNet
technology perspectives. While some use-specific security
considerations are discussed above, a more comprehensive discussion
of such considerations is captured in DetNet Security Considerations
[I-D.ietf-detnet-security]. Readers are encouraged to review this
Grossman Expires June 22, 2019 [Page 73]
Internet-Draft DetNet Use Cases December 2018
document to gain a more complete understanding of DetNet related
security considerations.
13. Contributors
RFC7322 limits the number of authors listed on the front page of a
draft to a maximum of 5, far fewer than the 20 individuals below who
made important contributions to this draft. The editor wishes to
thank and acknowledge each of the following authors for contributing
text to this draft. See also Section 14.
Craig Gunther (Harman International)
10653 South River Front Parkway, South Jordan,UT 84095
phone +1 801 568-7675, email craig.gunther@harman.com
Pascal Thubert (Cisco Systems, Inc)
Building D, 45 Allee des Ormes - BP1200, MOUGINS
Sophia Antipolis 06254 FRANCE
phone +33 497 23 26 34, email pthubert@cisco.com
Patrick Wetterwald (Cisco Systems)
45 Allees des Ormes, Mougins, 06250 FRANCE
phone +33 4 97 23 26 36, email pwetterw@cisco.com
Jean Raymond (Hydro-Quebec)
1500 University, Montreal, H3A3S7, Canada
phone +1 514 840 3000, email raymond.jean@hydro.qc.ca
Jouni Korhonen (Broadcom Corporation)
3151 Zanker Road, San Jose, 95134, CA, USA
email jouni.nospam@gmail.com
Yu Kaneko (Toshiba)
1 Komukai-Toshiba-cho, Saiwai-ku, Kasasaki-shi, Kanagawa, Japan
email yu1.kaneko@toshiba.co.jp
Subir Das (Vencore Labs)
150 Mount Airy Road, Basking Ridge, New Jersey, 07920, USA
email sdas@appcomsci.com
Balazs Varga (Ericsson)
Konyves Kalman krt. 11/B, Budapest, Hungary, 1097
email balazs.a.varga@ericsson.com
Janos Farkas (Ericsson)
Konyves Kalman krt. 11/B, Budapest, Hungary, 1097
email janos.farkas@ericsson.com
Grossman Expires June 22, 2019 [Page 74]
Internet-Draft DetNet Use Cases December 2018
Franz-Josef Goetz (Siemens)
Gleiwitzerstr. 555, Nurnberg, Germany, 90475
email franz-josef.goetz@siemens.com
Juergen Schmitt (Siemens)
Gleiwitzerstr. 555, Nurnberg, Germany, 90475
email juergen.jues.schmitt@siemens.com
Xavier Vilajosana (Worldsensing)
483 Arago, Barcelona, Catalonia, 08013, Spain
email xvilajosana@worldsensing.com
Toktam Mahmoodi (King's College London)
Strand, London WC2R 2LS, United Kingdom
email toktam.mahmoodi@kcl.ac.uk
Spiros Spirou (Intracom Telecom)
19.7 km Markopoulou Ave., Peania, Attiki, 19002, Greece
email spiros.spirou@gmail.com
Petra Vizarreta (Technical University of Munich)
Maxvorstadt, ArcisstraBe 21, Munich, 80333, Germany
email petra.stojsavljevic@tum.de
Daniel Huang (ZTE Corporation, Inc.)
No. 50 Software Avenue, Nanjing, Jiangsu, 210012, P.R. China
email huang.guangping@zte.com.cn
Xuesong Geng (Huawei Technologies)
email gengxuesong@huawei.com
Diego Dujovne (Universidad Diego Portales)
email diego.dujovne@mail.udp.cl
Maik Seewald (Cisco Systems)
email maseewal@cisco.com
14. Acknowledgments
14.1. Pro Audio
This section was derived from draft-gunther-detnet-proaudio-req-01.
The editors would like to acknowledge the help of the following
individuals and the companies they represent:
Jeff Koftinoff, Meyer Sound
Grossman Expires June 22, 2019 [Page 75]
Internet-Draft DetNet Use Cases December 2018
Jouni Korhonen, Associate Technical Director, Broadcom
Pascal Thubert, CTAO, Cisco
Kieran Tyrrell, Sienda New Media Technologies GmbH
14.2. Utility Telecom
This section was derived from draft-wetterwald-detnet-utilities-reqs-
02.
Faramarz Maghsoodlou, Ph. D. IoT Connected Industries and Energy
Practice Cisco
Pascal Thubert, CTAO Cisco
The wind power generation use case has been extracted from the study
of Wind Farms conducted within the 5GPPP Virtuwind Project. The
project is funded by the European Union's Horizon 2020 research and
innovation programme under grant agreement No 671648 (VirtuWind).
14.3. Building Automation Systems
This section was derived from draft-bas-usecase-detnet-00.
14.4. Wireless for Industrial Applications
This section was derived from draft-thubert-6tisch-4detnet-01.
This specification derives from the 6TiSCH architecture, which is the
result of multiple interactions, in particular during the 6TiSCH
(bi)Weekly Interim call, relayed through the 6TiSCH mailing list at
the IETF.
The authors wish to thank: Kris Pister, Thomas Watteyne, Xavier
Vilajosana, Qin Wang, Tom Phinney, Robert Assimiti, Michael
Richardson, Zhuo Chen, Malisa Vucinic, Alfredo Grieco, Martin Turon,
Dominique Barthel, Elvis Vogli, Guillaume Gaillard, Herman Storey,
Maria Rita Palattella, Nicola Accettura, Patrick Wetterwald, Pouria
Zand, Raghuram Sudhaakar, and Shitanshu Shah for their participation
and various contributions.
14.5. Cellular Radio
This section was derived from draft-korhonen-detnet-telreq-00.
Grossman Expires June 22, 2019 [Page 76]
Internet-Draft DetNet Use Cases December 2018
14.6. Industrial Machine to Machine (M2M)
The authors would like to thank Feng Chen and Marcel Kiessling for
their comments and suggestions.
14.7. Internet Applications and CoMP
This section was derived from draft-zha-detnet-use-case-00 by Yiyong
Zha.
This document has benefited from reviews, suggestions, comments and
proposed text provided by the following members, listed in
alphabetical order: Jing Huang, Junru Lin, Lehong Niu and Oilver
Huang.
14.8. Network Slicing
This section was written by Xuesong Geng, who would like to
acknowledge Norm Finn and Mach Chen for their useful comments.
14.9. Mining
This section was written by Diego Dujovne in conjunction with Xavier
Vilasojana.
14.10. Private Blockchain
This section was written by Daniel Huang.
15. IANA Considerations
This memo includes no requests from IANA.
16. Informative References
[Ahm14] Ahmed, M. and R. Kim, "Communication network architectures
for smart-wind power farms.", Energies, p. 3900-3921. ,
June 2014.
[bacnetip]
ASHRAE, "Annex J to ANSI/ASHRAE 135-1995 - BACnet/IP",
January 1999.
[CoMP] NGMN Alliance, "RAN EVOLUTION PROJECT COMP EVALUATION AND
ENHANCEMENT", NGMN Alliance NGMN_RANEV_D3_CoMP_Evaluation_
and_Enhancement_v2.0, March 2015,
<https://www.ngmn.org/uploads/media/
NGMN_RANEV_D3_CoMP_Evaluation_and_Enhancement_v2.0.pdf>.
Grossman Expires June 22, 2019 [Page 77]
Internet-Draft DetNet Use Cases December 2018
[CONTENT_PROTECTION]
Olsen, D., "1722a Content Protection", 2012,
<http://grouper.ieee.org/groups/1722/contributions/2012/
avtp_dolsen_1722a_content_protection.pdf>.
[CPRI] CPRI Cooperation, "Common Public Radio Interface (CPRI);
Interface Specification", CPRI Specification V6.1, July
2014, <http://www.cpri.info/downloads/
CPRI_v_6_1_2014-07-01.pdf>.
[DCI] Digital Cinema Initiatives, LLC, "DCI Specification,
Version 1.2", 2012, <http://www.dcimovies.com/>.
[eCPRI] IEEE Standards Association, "Common Public Radio
Interface, "Common Public Radio Interface: eCPRI Interface
Specification V1.0", 2017, <http://www.cpri.info/>.
[ESPN_DC2]
Daley, D., "ESPN's DC2 Scales AVB Large", 2014,
<http://sportsvideo.org/main/blog/2014/06/
espns-dc2-scales-avb-large>.
[flnet] Japan Electrical Manufacturers Association, "JEMA 1479 -
English Edition", September 2012.
[Fronthaul]
Chen, D. and T. Mustala, "Ethernet Fronthaul
Considerations", IEEE 1904.3, February 2015,
<http://www.ieee1904.org/3/meeting_archive/2015/02/
tf3_1502_che n_1a.pdf>.
[I-D.ietf-6tisch-6top-interface]
Wang, Q. and X. Vilajosana, "6TiSCH Operation Sublayer
(6top) Interface", draft-ietf-6tisch-6top-interface-04
(work in progress), July 2015.
[I-D.ietf-6tisch-architecture]
Thubert, P., "An Architecture for IPv6 over the TSCH mode
of IEEE 802.15.4", draft-ietf-6tisch-architecture-19 (work
in progress), December 2018.
[I-D.ietf-6tisch-coap]
Sudhaakar, R. and P. Zand, "6TiSCH Resource Management and
Interaction using CoAP", draft-ietf-6tisch-coap-03 (work
in progress), March 2015.
Grossman Expires June 22, 2019 [Page 78]
Internet-Draft DetNet Use Cases December 2018
[I-D.ietf-detnet-architecture]
Finn, N., Thubert, P., Varga, B., and J. Farkas,
"Deterministic Networking Architecture", draft-ietf-
detnet-architecture-09 (work in progress), October 2018.
[I-D.ietf-detnet-problem-statement]
Finn, N. and P. Thubert, "Deterministic Networking Problem
Statement", draft-ietf-detnet-problem-statement-08 (work
in progress), December 2018.
[I-D.ietf-detnet-security]
Mizrahi, T., Grossman, E., Hacker, A., Das, S., Dowdell,
J., Austad, H., Stanton, K., and N. Finn, "Deterministic
Networking (DetNet) Security Considerations", draft-ietf-
detnet-security-03 (work in progress), October 2018.
[I-D.ietf-tictoc-1588overmpls]
Davari, S., Oren, A., Bhatia, M., Roberts, P., and L.
Montini, "Transporting Timing messages over MPLS
Networks", draft-ietf-tictoc-1588overmpls-07 (work in
progress), October 2015.
[I-D.kh-spring-ip-ran-use-case]
Khasnabish, B., hu, f., and L. Contreras, "Segment Routing
in IP RAN use case", draft-kh-spring-ip-ran-use-case-02
(work in progress), November 2014.
[I-D.svshah-tsvwg-deterministic-forwarding]
Shah, S. and P. Thubert, "Deterministic Forwarding PHB",
draft-svshah-tsvwg-deterministic-forwarding-04 (work in
progress), August 2015.
[I-D.wang-6tisch-6top-sublayer]
Wang, Q. and X. Vilajosana, "6TiSCH Operation Sublayer
(6top)", draft-wang-6tisch-6top-sublayer-04 (work in
progress), November 2015.
[IEC-60870-5-104]
International Electrotechnical Commission, "International
Standard IEC 60870-5-104: Network access for IEC
60870-5-101 using standard transport profiles", June 2006.
[IEC61400]
"International standard 61400-25: Communications for
monitoring and control of wind power plants", June 2013.
Grossman Expires June 22, 2019 [Page 79]
Internet-Draft DetNet Use Cases December 2018
[IEEE1588]
IEEE, "IEEE Standard for a Precision Clock Synchronization
Protocol for Networked Measurement and Control Systems",
IEEE Std 1588-2008, 2008,
<http://standards.ieee.org/findstds/
standard/1588-2008.html>.
[IEEE1646]
"Communication Delivery Time Performance Requirements for
Electric Power Substation Automation", IEEE Standard
1646-2004 , Apr 2004.
[IEEE1722]
IEEE, "1722-2011 - IEEE Standard for Layer 2 Transport
Protocol for Time Sensitive Applications in a Bridged
Local Area Network", IEEE Std 1722-2011, 2011,
<http://standards.ieee.org/findstds/
standard/1722-2011.html>.
[IEEE19143]
IEEE Standards Association, "P1914.3/D3.1 Draft Standard
for Radio over Ethernet Encapsulations and Mappings",
IEEE 1914.3, 2018,
<https://standards.ieee.org/develop/project/1914.3.html>.
[IEEE802.1TSNTG]
IEEE Standards Association, "IEEE 802.1 Time-Sensitive
Networks Task Group", March 2013,
<http://www.ieee802.org/1/pages/avbridges.html>.
[IEEE802154]
IEEE standard for Information Technology, "IEEE std.
802.15.4, Part. 15.4: Wireless Medium Access Control (MAC)
and Physical Layer (PHY) Specifications for Low-Rate
Wireless Personal Area Networks".
[IEEE802154e]
IEEE standard for Information Technology, "IEEE standard
for Information Technology, IEEE std. 802.15.4, Part.
15.4: Wireless Medium Access Control (MAC) and Physical
Layer (PHY) Specifications for Low-Rate Wireless Personal
Area Networks, June 2011 as amended by IEEE std.
802.15.4e, Part. 15.4: Low-Rate Wireless Personal Area
Networks (LR-WPANs) Amendment 1: MAC sublayer", April
2012.
Grossman Expires June 22, 2019 [Page 80]
Internet-Draft DetNet Use Cases December 2018
[IEEE8021AS]
IEEE, "Timing and Synchronizations (IEEE 802.1AS-2011)",
IEEE 802.1AS-2001, 2011,
<http://standards.ieee.org/getIEEE802/
download/802.1AS-2011.pdf>.
[IEEE8021CM]
Farkas, J., "Time-Sensitive Networking for Fronthaul",
Unapproved PAR, PAR for a New IEEE Standard;
IEEE P802.1CM, April 2015,
<http://www.ieee802.org/1/files/public/docs2015/
new-P802-1CM-dr aft-PAR-0515-v02.pdf>.
[ISA100] ISA/ANSI, "ISA100, Wireless Systems for Automation",
<https://www.isa.org/isa100/>.
[knx] KNX Association, "ISO/IEC 14543-3 - KNX", November 2006.
[lontalk] ECHELON, "LonTalk(R) Protocol Specification Version 3.0",
1994.
[MEF22.1.1]
MEF, "Mobile Backhaul Phase 2 Amendment 1 -- Small Cells",
MEF 22.1.1, July 2014,
<http://www.mef.net/Assets/Technical_Specifications/PDF/
MEF_22.1.1.pdf>.
[MEF8] MEF, "Implementation Agreement for the Emulation of PDH
Circuits over Metro Ethernet Networks", MEF 8, October
2004,
<https://www.mef.net/Assets/Technical_Specifications/PDF/
MEF_8.pdf>.
[METIS] METIS, "Scenarios, requirements and KPIs for 5G mobile and
wireless system", ICT-317669-METIS/D1.1 ICT-
317669-METIS/D1.1, April 2013, <https://www.metis2020.com/
wp-content/uploads/deliverables/METIS_D1.1_v1.pdf>.
[modbus] Modbus Organization, "MODBUS APPLICATION PROTOCOL
SPECIFICATION V1.1b", December 2006.
[MODBUS] Modbus Organization, Inc., "MODBUS Application Protocol
Specification", Apr 2012.
[NGMN] NGMN Alliance, "5G White Paper", NGMN 5G White Paper v1.0,
February 2015, <https://www.ngmn.org/uploads/media/
NGMN_5G_White_Paper_V1_0.pdf>.
Grossman Expires June 22, 2019 [Page 81]
Internet-Draft DetNet Use Cases December 2018
[NGMN-fronth]
NGMN Alliance, "Fronthaul Requirements for C-RAN", March
2015, <https://www.ngmn.org/uploads/media/
NGMN_RANEV_D1_C-RAN_Fronthaul_Requirements_v1.0.pdf>.
[OPCXML] OPC Foundation, "OPC XML-Data Access Specification", Dec
2004.
[PCE] IETF, "Path Computation Element",
<https://datatracker.ietf.org/doc/charter-ietf-pce/>.
[profibus]
IEC, "IEC 61158 Type 3 - Profibus DP", January 2001.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031,
DOI 10.17487/RFC3031, January 2001,
<https://www.rfc-editor.org/info/rfc3031>.
[RFC3411] Harrington, D., Presuhn, R., and B. Wijnen, "An
Architecture for Describing Simple Network Management
Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
DOI 10.17487/RFC3411, December 2002,
<https://www.rfc-editor.org/info/rfc3411>.
[RFC3985] Bryant, S., Ed. and P. Pate, Ed., "Pseudo Wire Emulation
Edge-to-Edge (PWE3) Architecture", RFC 3985,
DOI 10.17487/RFC3985, March 2005,
<https://www.rfc-editor.org/info/rfc3985>.
[RFC4553] Vainshtein, A., Ed. and YJ. Stein, Ed., "Structure-
Agnostic Time Division Multiplexing (TDM) over Packet
(SAToP)", RFC 4553, DOI 10.17487/RFC4553, June 2006,
<https://www.rfc-editor.org/info/rfc4553>.
[RFC5086] Vainshtein, A., Ed., Sasson, I., Metz, E., Frost, T., and
P. Pate, "Structure-Aware Time Division Multiplexed (TDM)
Circuit Emulation Service over Packet Switched Network
(CESoPSN)", RFC 5086, DOI 10.17487/RFC5086, December 2007,
<https://www.rfc-editor.org/info/rfc5086>.
[RFC5087] Stein, Y(J)., Shashoua, R., Insler, R., and M. Anavi,
"Time Division Multiplexing over IP (TDMoIP)", RFC 5087,
DOI 10.17487/RFC5087, December 2007,
<https://www.rfc-editor.org/info/rfc5087>.
Grossman Expires June 22, 2019 [Page 82]
Internet-Draft DetNet Use Cases December 2018
[RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
"Network Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
<https://www.rfc-editor.org/info/rfc5905>.
[RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
Low-Power and Lossy Networks", RFC 6550,
DOI 10.17487/RFC6550, March 2012,
<https://www.rfc-editor.org/info/rfc6550>.
[RFC6551] Vasseur, JP., Ed., Kim, M., Ed., Pister, K., Dejean, N.,
and D. Barthel, "Routing Metrics Used for Path Calculation
in Low-Power and Lossy Networks", RFC 6551,
DOI 10.17487/RFC6551, March 2012,
<https://www.rfc-editor.org/info/rfc6551>.
[RFC7554] Watteyne, T., Ed., Palattella, M., and L. Grieco, "Using
IEEE 802.15.4e Time-Slotted Channel Hopping (TSCH) in the
Internet of Things (IoT): Problem Statement", RFC 7554,
DOI 10.17487/RFC7554, May 2015,
<https://www.rfc-editor.org/info/rfc7554>.
[RFC8169] Mirsky, G., Ruffini, S., Gray, E., Drake, J., Bryant, S.,
and A. Vainshtein, "Residence Time Measurement in MPLS
Networks", RFC 8169, DOI 10.17487/RFC8169, May 2017,
<https://www.rfc-editor.org/info/rfc8169>.
[Spe09] Sperotto, A., Sadre, R., Vliet, F., and A. Pras, "A First
Look into SCADA Network Traffic", IP Operations and
Management, p. 518-521. , June 2009.
[SRP_LATENCY]
Gunther, C., "Specifying SRP Latency", 2014,
<http://www.ieee802.org/1/files/public/docs2014/
cc-cgunther-acceptable-latency-0314-v01.pdf>.
[SyncE] ITU-T, "G.8261 : Timing and synchronization aspects in
packet networks", Recommendation G.8261, August 2013,
<http://www.itu.int/rec/T-REC-G.8261>.
[TR38501] 3GPP, "3GPP TS 38.501, Technical Specification System
Architecture for the 5G System (Release 15)", 2017,
<https://portal.3gpp.org/desktopmodules/Specifications/
SpecificationDetails.aspx?specificationId=3144>.
Grossman Expires June 22, 2019 [Page 83]
Internet-Draft DetNet Use Cases December 2018
[TR38801] 3GPP, "3GPP TR 38.801, Technical Specification Group Radio
Access Network; Study on new radio access technology:
Radio access architecture and interfaces (Release 14)",
2017,
<https://portal.3gpp.org/desktopmodules/Specifications/
SpecificationDetails.aspx?specificationId=3056>.
[TS23401] 3GPP, "General Packet Radio Service (GPRS) enhancements
for Evolved Universal Terrestrial Radio Access Network
(E-UTRAN) access", 3GPP TS 23.401 10.10.0, March 2013.
[TS25104] 3GPP, "Base Station (BS) radio transmission and reception
(FDD)", 3GPP TS 25.104 3.14.0, March 2007.
[TS36104] 3GPP, "Evolved Universal Terrestrial Radio Access
(E-UTRA); Base Station (BS) radio transmission and
reception", 3GPP TS 36.104 10.11.0, July 2013.
[TS36133] 3GPP, "Evolved Universal Terrestrial Radio Access
(E-UTRA); Requirements for support of radio resource
management", 3GPP TS 36.133 12.7.0, April 2015.
[TS36211] 3GPP, "Evolved Universal Terrestrial Radio Access
(E-UTRA); Physical channels and modulation", 3GPP
TS 36.211 10.7.0, March 2013.
[TS36300] 3GPP, "Evolved Universal Terrestrial Radio Access (E-UTRA)
and Evolved Universal Terrestrial Radio Access Network
(E-UTRAN); Overall description; Stage 2", 3GPP TS 36.300
10.11.0, September 2013.
[TSNTG] IEEE Standards Association, "IEEE 802.1 Time-Sensitive
Networks Task Group", 2013,
<http://www.IEEE802.org/1/pages/avbridges.html>.
[WirelessHART]
www.hartcomm.org, "Industrial Communication Networks -
Wireless Communication Network and Communication Profiles
- WirelessHART - IEC 62591", 2010.
Appendix A. Use Cases Explicitly Out of Scope for DetNet
This section contains use case text that has been determined to be
outside of the scope of the present DetNet work.
Grossman Expires June 22, 2019 [Page 84]
Internet-Draft DetNet Use Cases December 2018
A.1. DetNet Scope Limitations
The scope of DetNet is deliberately limited to specific use cases
that are consistent with the WG charter, subject to the
interpretation of the WG. At the time the DetNet Use Cases were
solicited and provided by the authors the scope of DetNet was not
clearly defined, and as that clarity has emerged, certain of the use
cases have been determined to be outside the scope of the present
DetNet work. Such text has been moved into this section to clarify
that these use cases will not be supported by the DetNet work.
The text in this section was moved here based on the following
"exclusion" principles. Or, as an alternative to moving all such
text to this section, some draft text has been modified in situ to
reflect these same principles.
The following principles have been established to clarify the scope
of the present DetNet work.
o The scope of network addressed by DetNet is limited to networks
that can be centrally controlled, i.e. an "enterprise" aka
"corporate" network. This explicitly excludes "the open
Internet".
o Maintaining synchronized time across a DetNet network is crucial
to its operation, however DetNet assumes that time is to be
maintained using other means, for example (but not limited to)
Precision Time Protocol ([IEEE1588]). A use case may state the
accuracy and reliability that it expects from the DetNet network
as part of a whole system, however it is understood that such
timing properties are not guaranteed by DetNet itself. At the
time of this writing it is an open question as to whether DetNet
protocols will include a way for an application to communicate
such timing expectations to the network, and if so whether they
would be expected to materially affect the performance they would
receive from the network as a result.
A.2. Internet-based Applications
There are many applications that communicate over the open Internet
that could benefit from guaranteed delivery and bounded latency.
However as noted above, all such applications when run over the open
Internet are out of scope for DetNet. These same applications may be
in-scope when run in constrained environments, i.e. within a
centrally controlled DetNet network. The following are some examples
of such applications.
Grossman Expires June 22, 2019 [Page 85]
Internet-Draft DetNet Use Cases December 2018
A.2.1. Use Case Description
A.2.1.1. Media Content Delivery
Media content delivery continues to be an important use of the
Internet, yet users often experience poor quality audio and video due
to the delay and jitter inherent in today's Internet.
A.2.1.2. Online Gaming
Online gaming is a significant part of the gaming market, however
latency can degrade the end user experience. For example "First
Person Shooter" games are highly delay-sensitive.
A.2.1.3. Virtual Reality
Virtual reality has many commercial applications including real
estate presentations, remote medical procedures, and so on. Low
latency is critical to interacting with the virtual world because
perceptual delays can cause motion sickness.
A.2.2. Internet-Based Applications Today
Internet service today is by definition "best-effort", with no
guarantees on delivery or bandwidth.
A.2.3. Internet-Based Applications Future
An Internet from which one can play a video without glitches and play
games without lag.
For online gaming, the maximum round-trip delay can be 100ms and
stricter for FPS gaming which can be 10-50ms. Transport delay is the
dominate part with a 5-20ms budget.
For VR, 1-10ms maximum delay is needed and total network budget is
1-5ms if doing remote VR.
Flow identification can be used for gaming and VR, i.e. it can
recognize a critical flow and provide appropriate latency bounds.
A.2.4. Internet-Based Applications Asks
o Unified control and management protocols to handle time-critical
data flow
o Application-aware flow filtering mechanism to recognize the timing
critical flow without doing 5-tuple matching
Grossman Expires June 22, 2019 [Page 86]
Internet-Draft DetNet Use Cases December 2018
o Unified control plane to provide low latency service on Layer-3
without changing the data plane
o OAM system and protocols which can help to provide E2E-delay
sensitive service provisioning
A.3. Pro Audio and Video - Digital Rights Management (DRM)
This section was moved here because this is considered a Link layer
topic, not direct responsibility of DetNet.
Digital Rights Management (DRM) is very important to the audio and
video industries. Any time protected content is introduced into a
network there are DRM concerns that must be maintained (see
[CONTENT_PROTECTION]). Many aspects of DRM are outside the scope of
network technology, however there are cases when a secure link
supporting authentication and encryption is required by content
owners to carry their audio or video content when it is outside their
own secure environment (for example see [DCI]).
As an example, two techniques are Digital Transmission Content
Protection (DTCP) and High-Bandwidth Digital Content Protection
(HDCP). HDCP content is not approved for retransmission within any
other type of DRM, while DTCP may be retransmitted under HDCP.
Therefore if the source of a stream is outside of the network and it
uses HDCP protection it is only allowed to be placed on the network
with that same HDCP protection.
A.4. Pro Audio and Video - Link Aggregation
Note: The term "Link Aggregation" is used here as defined by the text
in the following paragraph, i.e. not following a more common Network
Industry definition.
For transmitting streams that require more bandwidth than a single
link in the target network can support, link aggregation is a
technique for combining (aggregating) the bandwidth available on
multiple physical links to create a single logical link of the
required bandwidth. However, if aggregation is to be used, the
network controller (or equivalent) must be able to determine the
maximum latency of any path through the aggregate link.
A.5. Pro Audio and Video - Deterministic Time to Establish Streaming
The DetNet Working Group has decided that guidelines for establishing
a deterministic time to establish stream startup are not within scope
of DetNet. If bounded timing of establishing or re-establish streams
Grossman Expires June 22, 2019 [Page 87]
Internet-Draft DetNet Use Cases December 2018
is required in a given use case, it is up to the application/system
to achieve this.
Author's Address
Ethan Grossman (editor)
Dolby Laboratories, Inc.
1275 Market Street
San Francisco, CA 94103
USA
Phone: +1 415 645 4726
Email: ethan.grossman@dolby.com
URI: http://www.dolby.com
Grossman Expires June 22, 2019 [Page 88]
