Internet DRAFT - draft-grossman-detnet-use-cases
draft-grossman-detnet-use-cases
Internet Engineering Task Force E. Grossman, Ed.
Internet-Draft DOLBY
Intended status: Informational C. Gunther
Expires: May 12, 2016 HARMAN
P. Thubert
P. Wetterwald
CISCO
J. Raymond
HYDRO-QUEBEC
J. Korhonen
BROADCOM
Y. Kaneko
Toshiba
S. Das
Applied Communication Sciences
Y. Zha
HUAWEI
November 9, 2015
Deterministic Networking Use Cases
draft-grossman-detnet-use-cases-01
Abstract
This draft documents requirements in several diverse industries to
establish multi-hop paths for characterized flows with deterministic
properties. In this context deterministic implies that streams can
be established which provide guaranteed bandwidth and latency which
can be established from either a Layer 2 or Layer 3 (IP) interface,
and which can co-exist on an IP network with best-effort traffic.
Additional requirements include optional redundant paths, very high
reliability paths, time synchronization, and clock distribution.
Industries considered include wireless for industrial applications,
professional audio, electrical utilities, building automation
systems, radio/mobile access networks, automotive, and gaming.
For each case, this document will identify the application, identify
representative solutions used today, and what new uses an IETF DetNet
solution may enable.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Pro Audio Use Cases . . . . . . . . . . . . . . . . . . . . . 5
2.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 5
2.2. Fundamental Stream Requirements . . . . . . . . . . . . . 6
2.2.1. Guaranteed Bandwidth . . . . . . . . . . . . . . . . 6
2.2.2. Bounded and Consistent Latency . . . . . . . . . . . 6
2.2.2.1. Optimizations . . . . . . . . . . . . . . . . . . 8
2.3. Additional Stream Requirements . . . . . . . . . . . . . 8
2.3.1. Deterministic Time to Establish Streaming . . . . . . 8
2.3.2. Use of Unused Reservations by Best-Effort Traffic . . 9
2.3.3. Layer 3 Interconnecting Layer 2 Islands . . . . . . . 9
2.3.4. Secure Transmission . . . . . . . . . . . . . . . . . 9
2.3.5. Redundant Paths . . . . . . . . . . . . . . . . . . . 10
2.3.6. Link Aggregation . . . . . . . . . . . . . . . . . . 10
2.3.7. Traffic Segregation . . . . . . . . . . . . . . . . . 10
2.3.7.1. Packet Forwarding Rules, VLANs and Subnets . . . 11
2.3.7.2. Multicast Addressing (IPv4 and IPv6) . . . . . . 11
2.4. Integration of Reserved Streams into IT Networks . . . . 11
2.5. Security Considerations . . . . . . . . . . . . . . . . . 11
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2.5.1. Denial of Service . . . . . . . . . . . . . . . . . . 12
2.5.2. Control Protocols . . . . . . . . . . . . . . . . . . 12
2.6. A State-of-the-Art Broadcast Installation Hits Technology
Limits . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.7. Acknowledgements . . . . . . . . . . . . . . . . . . . . 13
3. Utility Telecom Use Cases . . . . . . . . . . . . . . . . . . 13
3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 13
3.2. Telecommunications Trends and General telecommunications
Requirements . . . . . . . . . . . . . . . . . . . . . . 14
3.2.1. General Telecommunications Requirements . . . . . . . 14
3.2.1.1. Migration to Packet-Switched Network . . . . . . 15
3.2.2. Applications, Use cases and traffic patterns . . . . 16
3.2.2.1. Transmission use cases . . . . . . . . . . . . . 16
3.2.2.2. Distribution use case . . . . . . . . . . . . . . 26
3.2.2.3. Generation use case . . . . . . . . . . . . . . . 29
3.2.3. Specific Network topologies of Smart Grid
Applications . . . . . . . . . . . . . . . . . . . . 30
3.2.4. Precision Time Protocol . . . . . . . . . . . . . . . 31
3.3. IANA Considerations . . . . . . . . . . . . . . . . . . . 32
3.4. Security Considerations . . . . . . . . . . . . . . . . . 32
3.4.1. Current Practices and Their Limitations . . . . . . . 32
3.4.2. Security Trends in Utility Networks . . . . . . . . . 34
3.5. Acknowledgements . . . . . . . . . . . . . . . . . . . . 35
4. Building Automation Systems Use Cases . . . . . . . . . . . . 35
4.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 36
4.2. BAS Functionality . . . . . . . . . . . . . . . . . . . . 36
4.3. BAS Architecture . . . . . . . . . . . . . . . . . . . . 37
4.4. Deployment Model . . . . . . . . . . . . . . . . . . . . 39
4.5. Use cases and Field Network Requirements . . . . . . . . 40
4.5.1. Environmental Monitoring . . . . . . . . . . . . . . 41
4.5.2. Fire Detection . . . . . . . . . . . . . . . . . . . 41
4.5.3. Feedback Control . . . . . . . . . . . . . . . . . . 42
4.6. Security Considerations . . . . . . . . . . . . . . . . . 43
5. Wireless for Industrial Use Cases . . . . . . . . . . . . . . 44
5.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 44
5.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 45
5.3. 6TiSCH Overview . . . . . . . . . . . . . . . . . . . . . 45
5.3.1. TSCH and 6top . . . . . . . . . . . . . . . . . . . . 48
5.3.2. SlotFrames and Priorities . . . . . . . . . . . . . . 48
5.3.3. Schedule Management by a PCE . . . . . . . . . . . . 48
5.3.4. Track Forwarding . . . . . . . . . . . . . . . . . . 49
5.3.4.1. Transport Mode . . . . . . . . . . . . . . . . . 51
5.3.4.2. Tunnel Mode . . . . . . . . . . . . . . . . . . . 52
5.3.4.3. Tunnel Metadata . . . . . . . . . . . . . . . . . 53
5.4. Operations of Interest for DetNet and PCE . . . . . . . . 54
5.4.1. Packet Marking and Handling . . . . . . . . . . . . . 55
5.4.1.1. Tagging Packets for Flow Identification . . . . . 55
5.4.1.2. Replication, Retries and Elimination . . . . . . 55
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5.4.1.3. Differentiated Services Per-Hop-Behavior . . . . 56
5.4.2. Topology and capabilities . . . . . . . . . . . . . . 56
5.5. Security Considerations . . . . . . . . . . . . . . . . . 57
5.6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . 57
6. Cellular Radio Use Cases . . . . . . . . . . . . . . . . . . 57
6.1. Introduction and background . . . . . . . . . . . . . . . 58
6.2. Network architecture . . . . . . . . . . . . . . . . . . 61
6.3. Time synchronization requirements . . . . . . . . . . . . 62
6.4. Time-sensitive stream requirements . . . . . . . . . . . 63
6.5. Security considerations . . . . . . . . . . . . . . . . . 64
7. Other Use Cases . . . . . . . . . . . . . . . . . . . . . . . 64
7.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 65
7.2. Critical Delay Requirements . . . . . . . . . . . . . . . 66
7.3. Coordinated multipoint processing (CoMP) . . . . . . . . 66
7.3.1. CoMP Architecture . . . . . . . . . . . . . . . . . . 66
7.3.2. Delay Sensitivity in CoMP . . . . . . . . . . . . . . 67
7.4. Industrial Automation . . . . . . . . . . . . . . . . . . 68
7.5. Vehicle to Vehicle . . . . . . . . . . . . . . . . . . . 68
7.6. Gaming, Media and Virtual Reality . . . . . . . . . . . . 69
8. Use Case Common Elements . . . . . . . . . . . . . . . . . . 69
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 70
10. Informative References . . . . . . . . . . . . . . . . . . . 70
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 79
1. Introduction
This draft presents use cases from diverse industries which have in
common a need for deterministic streams, but which also differ
notably in their network topologies and specific desired behavior.
Together, they provide broad industry context for DetNet and a
yardstick against which proposed DetNet designs can be measured (to
what extent does a proposed design satisfy these various use cases?)
For DetNet, use cases explicitly do not define requirements; The
DetNet WG will consider the use cases, decide which elements are in
scope for DetNet, and the results will be incorporated into future
drafts. Similarly, the DetNet use case draft explicitly does not
suggest any specific design, architecture or protocols, which will be
topics of future drafts.
We present for each use case the answers to the following questions:
o What is the use case?
o How is it addressed today?
o How would you like it to be addressed in the future?
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o What do you want the IETF to deliver?
The level of detail in each use case should be sufficient to express
the relevant elements of the use case, but not more.
At the end we consider the use cases collectively, and examine the
most significant goals they have in common.
2. Pro Audio Use Cases
(This section was derived from draft-gunther-detnet-proaudio-req-01)
2.1. Introduction
The professional audio and video industry includes music and film
content creation, broadcast, cinema, and live exposition as well as
public address, media and emergency systems at large venues
(airports, stadiums, churches, theme parks). These industries have
already gone through the transition of audio and video signals from
analog to digital, however the 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 attempting to transition to packet based
infrastructure for distributing audio and video in order to reduce
cost, increase routing flexibility, and integrate with existing IT
infrastructure.
However, there are several requirements for making a network the
primary infrastructure for audio and video which are not met by
todays networks and these are our concern in this draft.
The principal requirement is that pro audio and video applications
become able to establish streams that provide guaranteed (bounded)
bandwidth and latency from the Layer 3 (IP) interface. Such streams
can be created today within standards-based layer 2 islands however
these are not sufficient to enable effective distribution over wider
areas (for example broadcast events that span wide geographical
areas).
Some proprietary systems have been created which enable deterministic
streams at layer 3 however they are engineered networks in that they
require careful configuration to operate, often require that the
system be over designed, 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
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standards, and we believe that establishing relevant IETF standards
is a crucial factor.
It would be highly desirable if such streams could be routed over the
open Internet, however even intermediate solutions with more limited
scope (such as enterprise networks) can provide a substantial
improvement over todays networks, and a solution that only provides
for the enterprise network scenario is an acceptable first step.
We also present more fine grained requirements of the audio and video
industries such as safety and security, redundant paths, devices with
limited computing resources on the network, and that reserved stream
bandwidth is available for use by other best-effort traffic when that
stream is not currently in use.
2.2. Fundamental Stream Requirements
The fundamental stream properties are guaranteed bandwidth and
deterministic latency as described in this section. Additional
stream requirements are described in a subsequent section.
2.2.1. Guaranteed Bandwidth
Transmitting audio and video streams is unlike common file transfer
activities because guaranteed delivery 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 and
stream playback is interrupted, which is unacceptable in for example
a live concert. In some contexts large amounts of buffering can be
used to provide enough delay to allow time for one or more retries,
however this is not an effective solution when live interaction is
involved, and is not considered an acceptable general solution for
pro audio and video. (Have you ever tried speaking into a microphone
through a sound system that has an echo coming back at you? It makes
it almost impossible to speak clearly).
Providing a way to reserve a specific amount of bandwidth for a given
stream is a key requirement.
2.2.2. Bounded and Consistent Latency
Latency in this context means the amount of time that passes between
when a signal is sent over a stream and when it is received, for
example the amount of time delay between when you speak into a
microphone and when your voice emerges from the speaker. Any delay
longer than about 10-15 milliseconds is noticeable by most live
performers, and greater latency makes the system unusable because it
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prevents them from playing in time with the other players (see slide
6 of [SRP_LATENCY]).
The 15ms latency bound is made even more challenging because it is
often the case in network based music production with live electric
instruments that multiple stages of signal processing are used,
connected in series (i.e. from one to the other for example from
guitar through a series of digital effects processors) in which case
the latencies add, so the latencies of each individual stage must all
together remain less than 15ms.
In some situations it is acceptable at the local location for content
from the live remote site to be delayed to allow for a statistically
acceptable amount of latency in order to reduce jitter. However,
once the content begins playing in the local location any audio
artifacts caused by the local network are unacceptable, especially in
those situations where a live local performer is mixed into the feed
from the remote location.
In addition to being bounded to within some predictable and
acceptable amount of time (which may be 15 milliseconds or more or
less depending on the application) the latency also has to be
consistent. For example when playing a film consisting of a video
stream and audio stream over a network, those two streams must be
synchronized so that the voice and the picture match up. 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) buffer (delay) 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.
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2.2.2.1. Optimizations
The 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].
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.
2.3. Additional Stream Requirements
The requirements in this section are more specific yet are common to
multiple audio and video industry applications.
2.3.1. Deterministic Time to Establish Streaming
Some audio systems installed in public environments (airports,
hospitals) have unique requirements with regards to health, safety
and fire concerns. One such requirement is a maximum of 3 seconds
for a system to respond to an emergency detection and begin sending
appropriate warning signals and alarms without human intervention.
For this requirement to be met, the system must support a bounded and
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acceptable time from a notification signal to specific stream
establishment. For further details see [ISO7240-16].
Similar requirements apply when the system is restarted after a power
cycle, cable re-connection, or system reconfiguration.
In many cases such re-establishment of streaming state must be
achieved by the peer devices themselves, i.e. without a central
controller (since such a controller may only be present during
initial network configuration).
Video systems introduce related requirements, for example when
transitioning from one camera feed to another. Such systems
currently use purpose-built hardware to switch feeds smoothly,
however there is a current initiative in the broadcast industry to
switch to a packet-based infrastructure (see [STUDIO_IP] and the ESPN
DC2 use case described below).
2.3.2. 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 just reserve a ton of bandwidth and then never un-reserve
it even though they are not using it, and soon they will have no
bandwidth left.
2.3.3. Layer 3 Interconnecting Layer 2 Islands
As an intermediate step (short of providing guaranteed bandwidth
across the open internet) it would be valuable to provide a way to
connect multiple Layer 2 networks. For example layer 2 techniques
could be used to create a LAN for a single broadcast studio, and
several such studios could be interconnected via layer 3 links.
2.3.4. Secure Transmission
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
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[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.
2.3.5. Redundant Paths
On-air and other live media streams must be 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.
2.3.6. Link Aggregation
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 (see Bounded
and Consistent Latency section above).
2.3.7. 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
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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
requirement including (but not limited to) the following examples.
2.3.7.1. 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.
2.3.7.2. 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 required.
2.4. 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.
2.5. Security Considerations
Many industries that are moving from the point-to-point world to the
digital network world have little understanding of the pitfalls that
they can create for themselves with improperly implemented network
infrastructure. DetNet should consider ways to provide security
against DoS attacks in solutions directed at these markets. Some
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considerations are given here as examples of ways that we can help
new users avoid common pitfalls.
2.5.1. Denial of Service
One security pitfall that this author is aware of involves the use of
technology that allows a presenter to throw the content from their
tablet or smart phone onto the A/V system that is then viewed by all
those in attendance. The facility introducing this technology was
quite excited to allow such modern flexibility to those who came to
speak. One thing they hadn't realized was that since no security was
put in place around this technology it left a hole in the system that
allowed other attendees to "throw" their own content onto the A/V
system.
2.5.2. Control Protocols
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).
In addition, it would be desirable if the configuration protocols
that are used to create the network paths used by the professional
audio traffic could be designed to protect devices that are not meant
to receive high-amplitude content from having such potentially
damaging signals routed to them.
2.6. A State-of-the-Art Broadcast Installation Hits Technology Limits
ESPN recently 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 details at [ESPN_DC2] ).
In designing DC2 they replaced as much point-to-point technology as
they possibly 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, and
they were very happy with the results, however to interconnect these
layer 2 LAN islands together they ended up using dedicated links
because there is no standards-based routing solution available.
This is the kind of motivation we have to develop these standards
because customers are ready and able to use them.
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2.7. Acknowledgements
The editors would like to acknowledge the help of the following
individuals and the companies they represent:
Jeff Koftinoff, Meyer Sound
Jouni Korhonen, Associate Technical Director, Broadcom
Pascal Thubert, CTAO, Cisco
Kieran Tyrrell, Sienda New Media Technologies GmbH
3. Utility Telecom Use Cases
(This section was derived from draft-wetterwald-detnet-utilities-
reqs-02)
3.1. Overview
[I-D.finn-detnet-problem-statement] defines the characteristics of a
deterministic flow as a data communication flow with a bounded
latency, extraordinarily low frame loss, and a very narrow jitter.
This document intends to define the utility requirements for
deterministic networking.
Utility Telecom Networks
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.
Many utilities still rely on complex environments formed of multiple
application-specific, proprietary networks. Information is siloed
between operational areas. This prevents utility operations from
realizing the operational efficiency benefits, visibility, and
functional integration of operational information across grid
applications and data networks. The key to modernizing grid
telecommunications is to provide a common, adaptable, multi-service
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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 across disparate networks
and devices, as it has been already demonstrated in many mission-
critical and highly secure networks.
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. IPv6 is seen as the obvious future
telecommunications technology for the Smart Grid. The Adhoc Group
has disclosed, to the IEC coordination group, their conclusions at
the end of 2014.
It is imperative that utilities participate in standards development
bodies to influence the development of future solutions and to
benefit from shared experiences of other utilities and vendors.
3.2. Telecommunications Trends and General telecommunications
Requirements
These general telecommunications requirements are over and above the
specific requirements of the use cases that have been addressed so
far. These include both current and future telecommunications
related requirements that should be factored into the network
architecture and design.
3.2.1. General Telecommunications Requirements
o IP Connectivity everywhere
o Monitoring services everywhere and from different remote centers
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
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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
3.2.1.1. 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)
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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.
3.2.2. Applications, Use cases and traffic patterns
Among the numerous applications and use cases that a utility deploys
today, many rely on high availability and deterministic behaviour of
the telecommunications networks. Protection use cases and generation
control are the most demanding and can't rely on a best effort
approach.
3.2.2.1. Transmission use cases
Protection means not only the protection of the human operator but
also the protection of the electric equipments and the preservation
of the stability and frequency of the grid. If a default occurs on
the transmission or the distribution of the electricity, important
damages could occured to the human operator but also to very costly
electrical equipments and perturb the grid leading to blackouts. The
time and reliability requirements are very strong to avoid dramatic
impacts to the electrical infrastructure.
3.2.2.1.1. Tele Protection
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
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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.
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 key elements that may impact Teleprotection performance
include bandwidth rate of the Teleprotection system and its
resiliency or failure recovery capacity. Transmission time,
bandwidth utilization and resiliency are directly linked to the
telecommunications equipments and the connections that are used to
transfer the commands between relays.
3.2.2.1.1.1. Latency Budget Consideration
Delay requirements for utility networks may vary depending upon a
number of parameters, such as the specific protection equipments
used. 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.
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3.2.2.1.1.2. Asymetric delay
In addition to minimal transmission delay, a differential protection
telecommunications channel must be synchronous, i.e., experiencing
symmetrical channel delay in transmit and receive paths. This
requires special attention in jitter-prone packet networks. While
optimally Teleprotection systems should support zero asymmetric
delay, typical legacy relays can tolerate discrepancies of up to
750us.
The main tools available for lowering delay variation below this
threshold are:
o A jitter buffer 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. This is the
old TDM traditional way to fulfill this requirement.
o Traffic management tools ensure that the Teleprotection signals
receive the highest transmission priority and minimize the number
of jitter addition during the path. This is one way to meet the
requirement in IP networks.
o Standard Packet-Based synchronization technologies, such as
1588-2008 Precision Time Protocol (PTP) and Synchronous Ethernet
(Sync-E), can help maintain stable networks by keeping a highly
accurate clock source on the different network devices involved.
3.2.2.1.1.2.1. Other traffic characteristics
o Redundancy: The existence in a system of more than one means of
accomplishing a given function.
o Recovery time : The duration of time within which a business
process must be restored after any type of disruption in order to
avoid unacceptable consequences associated with a break in
business continuity.
o performance management : In networking, a management function
defined for controlling and analyzing different parameters/metrics
such as the throughput, error rate.
o packet loss : One or more packets of data travelling across
network fail to reach their destination.
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3.2.2.1.1.2.2. Teleprotection network requirements
The following table captures the main network requirements (this is
based on 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
3.2.2.1.2. Inter-Trip Protection scheme
Inter-tripping is the 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. The main use of such
schemes is to ensure that protection at both ends of a faulted
circuit will operate to isolate the equipment concerned. Inter-
tripping schemes use signaling to convey a trip command to remote
circuit breakers to isolate circuits.
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+--------------------------------+----------------------------------+
| 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
3.2.2.1.3. Current Differential Protection Scheme
Current differential protection is commonly used for line protection,
and is typical for protecting parallel circuits. A main advantage
for differential protection is that, compared to overcurrent
protection, it allows only the faulted circuit to be de-energized in
case of a fault. At both end of the lines, the current is measured
by the differential relays, and based on Kirchhoff's law, 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. A fault in line 1 will cause overcurrent to
be flowing in both lines, but because the current in line 2 is a
through following current, this current is measured equal at both
ends of the line, therefore the differential relays on line 2 will
not trip line 2. Line 1 will be tripped, as the relays will not
measure the same currents at both ends of the line. 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.
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+----------------------------------+--------------------------------+
| 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 requirements
3.2.2.1.4. Distance Protection Scheme
Distance (Impedance Relay) protection scheme is based on voltage and
current measurements. A fault on a circuit will generally create a
sag in the voltage level. If the ratio of voltage to current
measured at the protection relay terminals, which equates to an
impedance element, falls within a set threshold the circuit breaker
will operate. The operating characteristics of this protection are
based on the line characteristics. This means that when a fault
appears on the line, the impedance setting in the relay is compared
to the apparent impedance of the line from the relay terminals to the
fault. If the relay setting is determined to be below the apparent
impedance it is determined that the fault is within the zone of
protection. When the transmission line length is under a minimum
length, distance protection becomes more difficult to coordinate. In
these instances the best choice of protection is current differential
protection.
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+-------------------------------+-----------------------------------+
| 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
3.2.2.1.5. 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 merging unit 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.
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+----------------------------------+--------------------------------+
| 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
3.2.2.1.6. Intra-Substation Process Bus Communications
This use case describes the data flow from the CT/VT to the IEDs in
the substation via the merging unit (MU). The CT/VT in the
substation send the sampled value (analog voltage or current) to the
Merging Unit (MU) over hard wire. The merging unit sends the time-
synchronized 61850-9-2 sampled values to the IEDs in the substation
in GOOSE message format. The GPS Master Clock can send 1PPS or
IRIG-B format to MU through serial port, or IEEE 1588 protocol via
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.
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+----------------------------------+--------------------------------+
| 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
3.2.2.1.7. 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:
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+----------------------+--------------------------------------------+
| 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% |
+----------------------+--------------------------------------------+
Table 7: WAMS Special Communication Requirements
3.2.2.1.8. IEC 61850 WAN engineering guidelines requirement
classification
The IEC (International Electrotechnical Commission) has recently
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. You will find herafter the table
summarizing these requirements:
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+----------------+------------+------------+------------+-----------+
| 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
3.2.2.2. Distribution use case
3.2.2.2.1. Fault Location Isolation and Service Restoration (FLISR)
As the name implies, 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. It is a self-healing feature whose purpose is to minimize
the impact of faults by serving portions of the loads on the affected
circuit by switching to other circuits. It reduces the number of
customers that experience a sustained power outage by reconfiguring
distribution circuits. This will likely be the first wide spread
application of distributed intelligence in the grid. Secondary
substations can be connected to multiple primary substations.
Normally, static power switch statuses (open/closed) in the network
dictate the power flow to secondary substations. Reconfiguring the
network in the event of a fault is typically done manually on site to
operate switchgear to energize/de-energize alternate paths.
Automating the operation of substation switchgear allows the utility
to have a more dynamic network where the flow of power can be altered
under fault conditions but also during times of peak load. It allows
the utility to shift peak loads around the network. Or, to be more
precise, alters the configuration of the network to move loads
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between different primary substations. The FLISR capability can be
enabled in two modes:
o Managed centrally from DMS (Distribution Management System), or
o Executed locally through distributed control via intelligent
switches and fault sensors.
There are 3 distinct sub-functions that are performed:
1. Fault Location Identification
This sub-function is initiated by SCADA inputs, such as lockouts,
fault indications/location, and, also, by input from the Outage
Management System (OMS), and in the future by inputs from fault-
predicting devices. It determines the specific protective device,
which has cleared the sustained fault, identifies the de-energized
sections, and estimates the probable location of the actual or the
expected fault. It distinguishes faults cleared by controllable
protective devices from those cleared by fuses, and identifies
momentary outages and inrush/cold load pick-up currents. This step
is also referred to as Fault Detection Classification and Location
(FDCL). This step helps to expedite the restoration of faulted
sections through fast fault location identification and improved
diagnostic information available for crew dispatch. Also provides
visualization of fault information to design and implement a
switching plan to isolate the fault.
2. Fault Type Determination
I. Indicates faults cleared by controllable protective devices by
distinguishing between:
a. Faults cleared by fuses
b. Momentary outages
c. Inrush/cold load current
II. Determines the faulted sections based on SCADA fault indications
and protection lockout signals
III. Increases the accuracy of the fault location estimation based
on SCADA fault current measurements and real-time fault analysis
3. Fault Isolation and Service Restoration
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Once the location and type of the fault has been pinpointed, the
systems will attempt to isolate the fault and restore the non-faulted
section of the network. This can have three modes of operation:
I. Closed-loop mode : This is initiated by the Fault location sub-
function. It generates a switching order (i.e., sequence of
switching) for the remotely controlled switching devices to isolate
the faulted section, and restore service to the non-faulted sections.
The switching order is automatically executed via SCADA.
II. Advisory mode : This is initiated by the Fault location sub-
function. It generates a switching order for remotely and manually
controlled switching devices to isolate the faulted section, and
restore service to the non-faulted sections. The switching order is
presented to operator for approval and execution.
III. Study mode : the operator initiates this function. It analyzes
a saved case modified by the operator, and generates a switching
order under the operating conditions specified by the operator.
With the increasing volume of data that are collected through fault
sensors, utilities will use Big Data query and analysis tools to
study outage information to anticipate and prevent outages by
detecting failure patterns and their correlation with asset age,
type, load profiles, time of day, weather conditions, and other
conditions to discover conditions that lead to faults and take the
necessary preventive and corrective measures.
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+----------------------+--------------------------------------------+
| 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 9: FLISR Communication Requirements
3.2.2.3. Generation use case
3.2.2.3.1. Frequency Control / Automatic Generation Control (AGC)
The system frequency should be maintained within a very narrow band.
Deviations from the acceptable frequency range are detected and
forwarded to the Load Frequency Control (LFC) system so that required
up or down generation increase / decrease pulses can be sent to the
power plants for frequency regulation. The trend in system frequency
is a measure of mismatch between demand and generation, and is a
necessary parameter for load control in interconnected systems.
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. Since a power grid requires that generation and
load closely balance moment by moment, frequent adjustments to the
output of generators are necessary. The balance can be judged by
measuring the system frequency; if it is increasing, more power is
being generated than used, and all machines in the system are
accelerating. If the system frequency is decreasing, more demand is
on the system than the instantaneous generation can provide, and all
generators are slowing down.
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Where the grid has tie lines to adjacent control areas, automatic
generation control helps maintain the power interchanges over the tie
lines at the scheduled levels. The AGC takes into account various
parameters including the most economical units to adjust, the
coordination of thermal, hydroelectric, and other generation types,
and even constraints related to the stability of the system and
capacity of interconnections to other power grids.
For the purpose of AGC we use static frequency measurements and
averaging methods are used to get a more precise measure of system
frequency in steady-state conditions.
During disturbances, more real-time dynamic measurements of system
frequency are taken using PMUs, especially when different areas of
the system exhibit different frequencies. But that is outside the
scope of this use case.
+---------------------------------------------------+---------------+
| 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 10: FCAG Communication Requirements
3.2.3. 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
sites, and providing FCAPS (Fault. Configuration. Accounting.
Performance. Security) services from centralized network operation
centers.
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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 shall stay available so the
SPS 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.
Due to vast distances between transmission substations (for example
as far as 280km apart), the fiber signal can be amplified to reach a
distance of 280 km without attenuation.
3.2.4. 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 (IEEE 1588), distributing the synchronization
signal over the IP/MPLS network.
The Precision Time Protocol (PTP) is defined in IEEE standard 1588.
PTP is applicable to distributed systems consisting of one or more
nodes, communicating over a network. Nodes are modeled as containing
a real-time clock that may be used by applications within the node
for various purposes such as generating time-stamps for data or
ordering events managed by the node. The protocol 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
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tree protocol). PTP eliminates cyclic forwarding of PTP messages
between communication paths.
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.
PTP was designed assuming a multicast communication model. 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 asymmetry in the paths taken by event messages.
Asymmetry is not detectable by PTP, however, if known, PTP
corrects for asymmetry.
A time-stamp event is generated at the time of transmission and
reception of any event message. The time-stamp event occurs when the
message's timestamp point crosses the boundary between the node and
the network.
IEC 61850 will recommend the use of the IEEE PTP 1588 Utility Profile
(as defined in IEC 62439-3 Annex B) which offers the support of
redundant attachment of clocks to Paralell Redundancy Protcol (PRP)
and High-availability Seamless Redundancy (HSR) networks.
3.3. IANA Considerations
This memo includes no request to IANA.
3.4. Security Considerations
3.4.1. Current Practices and Their Limitations
Grid monitoring and control devices are already targets for cyber
attacks and legacy telecommunications protocols have many intrinsic
network related vulnerabilities. DNP3, Modbus, 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:
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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).
o Bump in the wire (BITW) solutions : A hardware device is added to
provide IPSec services between two routers that are not capable of
IPSec functions. This special IPsec device will intercept then
intercept outgoing datagrams, add IPSec protection to them, and
strip it off incoming datagrams. BITW can all IPSec to legacy
hosts and can retrofit non-IPSec routers to provide security
benefits. The disadvantages are complexity and cost.
These inherent vulnerabilities, along with increasing connectivity
between IT an OT networks, make network-based attacks very feasible.
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
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could provide both control over a process and misrepresentation of
data back to operator consoles.
3.4.2. Security Trends in Utility Networks
Although advanced telecommunications networks can assist in
transforming the energy industry, 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
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 : the telecommunications parties involved must be
validated as genuine
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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's 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:
1. IP enables a rich set of features and capabilities to enhance the
security posture
2. 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
levels of data privacy, device and platform integrity, and threat
detection and mitigation.
3.5. Acknowledgements
Faramarz Maghsoodlou, Ph. D. IoT Connected Industries and Energy
Practice Cisco
Pascal Thubert, CTAO Cisco
4. Building Automation Systems Use Cases
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4.1. Introduction
Building Automation System (BAS) is a system that manages various
equipment and sensors in buildings (e.g., heating, cooling and
ventilating) for improving residents' comfort, reduction of energy
consumption and automatic responses in case of failure and emergency.
For example, BAS measures temperature of a room by using various
sensors and then controls the HVAC (Heating, Ventilating, and air
Conditioning) system automatically to maintain the temperature level
and minimize the energy consumption.
There are typically two layers of network in a BAS. Upper one is
called management network and the lower one is called field network.
In management networks, an IP-based communication protocol is used
while in field network, non-IP based communication protocols (a.k.a.,
field protocol) are mainly used.
There are many field protocols used in today's deployment in which
some medium access control and physical layers protocols are
standards-based and others are proprietary based. Therefore the BAS
needs to have multiple MAC/PHY modules and interfaces to make use of
multiple field protocols based devices. This situation not only
makes BAS more expensive with large development cycle of multiple
devices but also creates the issue of vendor lock-in with multiple
types of management applications.
The other issue with some of the existing field networks and
protocols are security. When these protocols and network were
developed, it was assumed that the field networks are isolated
physically from external networks and therefore the network and
protocol security was not a concern. However, in today's world many
BASes are managed remotely and is connected to shared IP networks and
it is also not uncommon that same IT infrastructure is used be it
office, home or in enterprise networks. Adding network and protocol
security to existing system is a non-trivial task.
This document first describes the BAS functionalities, its
architecture and current deployment models. Then we discuss the use
cases and field network requirements that need to be satisfied by
deterministic networking.
4.2. BAS Functionality
Building Automation System (BAS) is a system that manages various
devices in buildings automatically. BAS primarily performs the
following functions:
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o Measures states of devices in a regular interval. For example,
temperature or humidity or illuminance of rooms, on/off state of
room lights, open/close state of doors, FAN speed, valve, running
mode of HVAC, and its power consumption.
o Stores the measured data into a database (Note: The database keeps
the data for several years).
o Provides the measured data for BAS operators for visualization.
o Generates alarms for abnormal state of devices (e.g., calling
operator's cellular phone, sending an e-mail to operators and so
on).
o Controls devices on demand.
o Controls devices with a pre-defined operation schedule (e.g., turn
off room lights at 10:00 PM).
4.3. BAS Architecture
A typical BAS architecture is described below in Figure 1. There are
several elements in a BAS.
+----------------------------+
| |
| BMS HMI |
| | | |
| +----------------------+ |
| | Management Network | |
| +----------------------+ |
| | | |
| LC LC |
| | | |
| +----------------------+ |
| | Field Network | |
| +----------------------+ |
| | | | | |
| Dev Dev Dev Dev |
| |
+----------------------------+
BMS := Building Management Server
HMI := Human Machine Interface
LC := Local Controller
Figure 1: BAS architecture
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Human Machine Interface (HMI): It is commonly a computing platform
(e.g., desktop PC) used by operators. Operators perform the
following operations through HMI.
o Monitoring devices: HMI displays measured device states. For
example, latest device states, a history chart of states, a popup
window with an alert message. Typically, the measured device
states are stored in BMS (Building Management Server).
o Controlling devices: HMI provides ability to control the devices.
For example, turn on a room light, set a target temperature to
HVAC. Several parameters (a target device, a control value,
etc.), can be set by the operators which then HMI sends to a LC
(Local Controller) via the management network.
o Configuring an operational schedule: HMI provides scheduling
capability through which operational schedule is defined. For
example, schedule includes 1) a time to control, 2) a target
device to control, and 3) a control value. A specific operational
example could be turn off all room lights in the building at 10:00
PM. This schedule is typically stored in BMS.
Building Management Server (BMS) collects device states from LCs
(Local Controllers) and stores it into a database. According to its
configuration, BMS executes the following operation automatically.
o BMS collects device states from LCs in a regular interval and then
stores the information into a database.
o BMS sends control values to LCs according to a pre-configured
schedule.
o BMS sends an alarm signal to operators if it detects abnormal
devices states. For example, turning on a red lamp, calling
operators' cellular phone, sending an e-mail to operators.
BMS and HMI communicate with Local Controllers (LCs) via IP-based
communication protocol standardized by BACnet/IP [bacnetip], KNX/IP
[knx]. These protocols are commonly called as management protocols.
LCs measure device states and provide the information to BMS or HMI.
These devices may include HVAC, FAN, doors, valves, lights, sensors
(e.g., temperature, humidity, and illuminance). LC can also set
control values to the devices. LC sometimes has additional
functions, for example, sending a device state to BMS or HMI if the
device state exceeds a certain threshold value, feedback control to a
device to keep the device state at a certain state. Typical example
of LC is a PLC (Programmable Logic Controller).
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Each LC is connected with a different field network and communicates
with several tens or hundreds of devices via the field network.
Today there are many field protocols used in the field network.
Based on the type of field protocol used, LC interfaces and its
hardware/software could be different. Field protocols are currently
non-IP based in which some of them are standards-based (e.g., LonTalk
[lontalk], Modbus [modbus], Profibus [profibus], FL-net [flnet],) and
others are proprietary.
4.4. Deployment Model
An example BAS system deployment model for medium and large buildings
is depicted in Figure 2 below. In this case the physical layout of
the entire system spans across multiple floors in which there is
normally 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.
+--------------------------------------------------+
| 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 2: Deployment model for Medium/Large Buildings
Each LC is then connected to the monitoring room via the management
network. In this scenario, the management functions are performed
locally and reside within the building. In most cases, fast Ethernet
(e.g. 100BASE-TX) is used for the management network. In the field
network, variety of physical interfaces such as RS232C, and RS485 are
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used. Since management network is non-real time, Ethernet without
quality of service is sufficient for today's deployment. However,
the requirements are different for field networks when they are
replaced by either Ethernet or any wireless technologies supporting
real time requirements (Section 3.4).
Figure 3 depicts a deployment model in which the management can be
hosted remotely. This deployment is becoming popular for small
office and residential buildings whereby having a standalone
monitoring system is not a cost effective solution. In such
scenario, multiple buildings are managed by a remote management
monitoring system.
+---------------+
| Remote Center |
| |
| BMS HMI |
+------------------------------------+ | | | |
| Floor 2 | | +---+---+ |
| +----LC~~~~+~~~~~+ Field Network| | | |
| | | | | | Router |
| | Dev Dev | +-------|-------+
| | | |
|--- | ------------------------------| |
| | Floor 1 | |
| +----LC~~~~+~~~~~+ | |
| | | | | |
| | Dev Dev | |
| | | |
| | Management Network | WAN |
| +------------------------Router-------------+
| |
+------------------------------------+
Figure 3: Deployment model for Small Buildings
In either case, interoperability today is only limited to the
management network and its protocols. In existing deployment, there
are limited interoperability opportunity in the field network due to
its nature of non-IP-based design and requirements.
4.5. Use cases and Field Network Requirements
In this section, we describe several use cases and corresponding
network requirements.
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4.5.1. Environmental Monitoring
In this use case, LCs measure environmental data (e.g. temperatures,
humidity, illuminance, CO2, etc.) from several sensor devices at each
measurement interval. LCs keep latest value of each sensor. BMS
sends data requests to LCs to collect the latest values, then stores
the collected values into a database. Operators check the latest
environmental data that are displayed by the HMI. BMS also checks
the collected data automatically to notify the operators if a room
condition was going to bad (e.g., too hot or cold). The following
table lists the field network requirements in which the number of
devices in a typical building will be ~100s per LC.
+----------------------+-------------+
| Metric | Requirement |
+----------------------+-------------+
| Measurement interval | 100 msec |
| | |
| Availability | 99.999 % |
+----------------------+-------------+
Table 11: Field Network Requirements for Environmental Monitoring
There is a case that BMS sends data requests at each 1 second in
order to draw a historical chart of 1 second granularity. Therefore
100 msec measurement interval is sufficient for this use case,
because typically 10 times granularity (compared with the interval of
data requests) is considered enough accuracy in this use case. A LC
needs to measure values of all sensors connected with itself at each
measurement interval. Each communication delay in this scenario is
not so critical. The important requirement is completing
measurements of all sensor values in the specified measurement
interval. The availability in this use case is very high (Three 9s).
4.5.2. Fire Detection
In the case of fire detection, HMI needs to show a popup window with
an alert message within a few seconds after an abnormal state is
detected. BMS needs to do some operations if it detects fire. For
example, stopping a HVAC, closing fire shutters, and turning on fire
sprinklers. The following table describes requirements in which the
number of devices in a typical building will be ~10s per LC.
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+----------------------+---------------+
| Metric | Requirement |
+----------------------+---------------+
| Measurement interval | 10s of msec |
| | |
| Communication delay | < 10s of msec |
| | |
| Availability | 99.9999 % |
+----------------------+---------------+
Table 12: Field Network Requirements for Fire Detection
In order to perform the above operation within a few seconds (1 or 2
seconds) after detecting fire, LCs should measure sensor values at a
regular interval of less than 10s of msec. If a LC detects an
abnormal sensor value, it sends an alarm information to BMS and HMI
immediately. BMS then controls HVAC or fire shutters or fire
sprinklers. HMI then displays a pop up window and generates the
alert message. Since the management network does not operate in real
time, and software run on BMS or HMI requires 100s of ms, the
communication delay should be less than ~10s of msec. The
availability in this use case is very high (Four 9s).
4.5.3. Feedback Control
Feedback control is used to keep a device state at a certain value.
For example, keeping a room temperature at 27 degree Celsius, keeping
a water flow rate at 100 L/m and so on. The target device state is
normally pre-defined in LCs or provided from BMS or from HMI.
In feedback control procedure, a LC repeats the following actions at
a regular interval (feedback interval).
1. The LC measures device states of the target device.
2. The LC calculates a control value by considering the measured
device state.
3. The LC sends the control value to the target device.
The feedback interval highly depends on the characteristics of the
device and a target quality of control value. While several tens of
milliseconds feedback interval is sufficient to control a valve that
regulates a water flow, controlling DC motors requires several
milliseconds interval. The following table describes the field
network requirements in which the number of devices in a typical
building will be ~10s per LC.
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+----------------------+---------------+
| Metric | Requirement |
+----------------------+---------------+
| Feedback interval | ~10ms - 100ms |
| | |
| Communication delay | < 10s of msec |
| | |
| Communication jitter | < 1 msec |
| | |
| Availability | 99.9999 % |
+----------------------+---------------+
Table 13: Field Network Requirements for Feedback Control
Small communication delay and jitter are required in this use case in
order to provide high quality of feedback control. This is currently
offered in production environment with hgh availability (Four 9s).
4.6. Security Considerations
Both network and physical security of BAS are important. While
physical security is present in today's deployment, adequate network
security and access control are either not implemented or configured
properly. This was sufficient in networks while they are isolated
and not connected to the IT or other infrastructure networks but when
IT and OT (Operational Technology) are connected in the same
infrastructure network, network security is essential. The
management network being an IP-based network does have the protocols
and knobs to enable the network security but in many cases BAS for
example, does not use device authentication or encryption for data in
transit. On the contrary, many of today's field networks do not
provide any security at all. Following are the high level security
requirements that the network should provide:
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
o Availability of network data for normal and disaster scenario
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5. Wireless for Industrial Use Cases
(This section was derived from draft-thubert-6tisch-4detnet-01)
5.1. Introduction
The emergence of wireless technology has enabled a variety of new
devices to get interconnected, at a very low marginal cost per
device, at any distance ranging from Near Field to interplanetary,
and in circumstances where wiring may not be practical, for instance
on fast-moving or rotating devices.
At the same time, a new breed of Time Sensitive Networks is being
developed to enable traffic that is highly sensitive to jitter, quite
sensitive to latency, and with a high degree of operational
criticality so that loss should be minimized at all times. Such
traffic is not limited to professional Audio/ Video networks, but is
also found in command and control operations such as industrial
automation and vehicular sensors and actuators.
At IEEE802.1, the Audio/Video Task Group [IEEE802.1TSNTG] Time
Sensitive Networking (TSN) to address Deterministic Ethernet. The
Medium access Control (MAC) of IEEE802.15.4 [IEEE802154] has evolved
with the new TimeSlotted Channel Hopping (TSCH) [RFC7554] mode for
deterministic industrial-type applications. TSCH was introduced with
the IEEE802.15.4e [IEEE802154e] amendment and will be wrapped up in
the next revision of the IEEE802.15.4 standard. For all practical
purpose, this document is expected to be insensitive to the future
versions of the IEEE802.15.4 standard, which is thus referenced
undated.
Though at a different time scale, both TSN and TSCH standards provide
Deterministic capabilities to the point that a packet that pertains
to a certain flow crosses the network from node to node following a
very precise schedule, as a train that leaves intermediate stations
at precise times along its path. With TSCH, time is formatted into
timeSlots, and an individual cell is allocated to unicast or
broadcast communication at the MAC level. The time-slotted operation
reduces collisions, saves energy, and enables to more closely
engineer the network for deterministic properties. The channel
hopping aspect is a simple and efficient technique to combat multi-
path fading and co-channel interferences (for example by Wi-Fi
emitters).
The 6TiSCH Architecture [I-D.ietf-6tisch-architecture] defines a
remote monitoring and scheduling management of a TSCH network by a
Path Computation Element (PCE), which cooperates with an abstract
Network Management Entity (NME) to manage timeSlots and device
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resources in a manner that minimizes the interaction with and the
load placed on the constrained devices.
This Architecture applies the concepts of Deterministic Networking on
a TSCH network to enable the switching of timeSlots in a G-MPLS
manner. This document details the dependencies that 6TiSCH has on
PCE [PCE] and DetNet [I-D.finn-detnet-architecture] to provide the
necessary capabilities that may be specific to such networks. In
turn, DetNet is expected to integrate and maintain consistency with
the work that has taken place and is continuing at IEEE802.1TSN and
AVnu.
5.2. Terminology
Readers are expected to be familiar with all the terms and concepts
that are discussed in "Multi-link Subnet Support in IPv6"
[I-D.ietf-ipv6-multilink-subnets].
The draft uses terminology defined or referenced in
[I-D.ietf-6tisch-terminology] and
[I-D.ietf-roll-rpl-industrial-applicability].
The draft also conforms to the terms and models described in
[RFC3444] and uses the vocabulary and the concepts defined in
[RFC4291] for the IPv6 Architecture.
5.3. 6TiSCH Overview
The scope of the present work is a subnet that, in its basic
configuration, is made of a TSCH [RFC7554] MAC Low Power Lossy
Network (LLN).
---+-------- ............ ------------
| 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 4: Basic Configuration of a 6TiSCH Network
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In the extended configuration, a Backbone Router (6BBR) federates
multiple 6TiSCH in a single subnet over a backbone. 6TiSCH 6BBRs
synchronize with one another over the backbone, so as to ensure that
the multiple LLNs that form the IPv6 subnet stay tightly
synchronized.
---+-------- ............ ------------
| 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 5: Extended Configuration of a 6TiSCH Network
If the Backbone is Deterministic, then the Backbone Router ensures
that the end-to-end deterministic behavior is maintained between the
LLN and the backbone. This SHOULD be done in conformance to the
DetNet Architecture [I-D.finn-detnet-architecture] which studies
Layer-3 aspects of Deterministic Networks, and covers networks that
span multiple Layer-2 domains. One particular requirement is that
the PCE MUST be able to compute a deterministic path and to end
across the TSCH network and an IEEE802.1 TSN Ethernet backbone, and
DetNet MUST enable end-to-end deterministic forwarding.
6TiSCH defines the concept of a Track, which is a complex form of a
uni-directional Circuit ([I-D.ietf-6tisch-terminology]). As opposed
to a simple circuit that is a sequence of nodes and links, a Track is
shaped as a directed acyclic graph towards a destination to support
multi-path forwarding and route around failures. A Track may also
branch off and rejoin, for the purpose of the so-called Packet
Replication and Elimination (PRE), over non congruent branches. PRE
may be used to complement layer-2 Automatic Repeat reQuest (ARQ) to
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meet industrial expectations in Packet Delivery Ratio (PDR), in
particular when the Track extends beyond the 6TiSCH network.
+-----+
| 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 6: End-to-End deterministic Track
In the example above, 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.
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
of the packet still makes it in due 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).
It is also possible that the field device only uses the second branch
if sending over the first branch fails.
In current deployments, 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
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and use the other in case of Layer-2 transmission failure as detected
by ARQ.
5.3.1. TSCH and 6top
6top 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 operations are specified in
[I-D.wang-6tisch-6top-sublayer].
The 6top data model and management interfaces are further discussed
in [I-D.ietf-6tisch-6top-interface] and [I-D.ietf-6tisch-coap].
The architecture defines "soft" cells and "hard" cells. "Hard" cells
are owned and managed by an separate scheduling entity (e.g. a PCE)
that specifies the slotOffset/channelOffset of the cells to be
added/moved/deleted, in which case 6top can only act as instructed,
and may not move hard cells in the TSCH schedule on its own.
5.3.2. SlotFrames and Priorities
A slotFrame is the base object that the PCE needs to manipulate to
program a schedule into an LLN node. Elaboration on that concept can
be found in section "SlotFrames and Priorities" of the 6TiSCH
architecture [I-D.ietf-6tisch-architecture]. The architecture also
details how the schedule is constructed and how transmission
resources called cells can be allocated to particular transmissions
so as to avoid collisions.
5.3.3. Schedule Management by a PCE
6TiSCH supports a mixed model of centralized routes and distributed
routes. Centralized routes can for example be computed by a entity
such as a PCE. Distributed routes are computed by RPL.
Both methods may inject routes in the Routing Tables of the 6TiSCH
routers. In either case, each route is associated with a 6TiSCH
topology that can be a RPL Instance topology or a track. The 6TiSCH
topology is indexed by a Instance ID, in a format that reuses the
RPLInstanceID as defined in RPL [RFC6550].
Both RPL and PCE rely on shared sources such as policies to define
Global and Local RPLInstanceIDs that can be used by either method.
It is possible for centralized and distributed routing to share a
same topology. Generally they will operate in different slotFrames,
and centralized routes will be used for scheduled traffic and will
have precedence over distributed routes in case of conflict between
the slotFrames.
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Section "Schedule Management Mechanisms" of the 6TiSCH architecture
describes 4 paradigms to manage the TSCH schedule of the LLN nodes:
Static Scheduling, neighbor-to-neighbor Scheduling, remote monitoring
and scheduling management, and Hop-by-hop scheduling. The Track
operation for DetNet corresponds to a remote monitoring and
scheduling management by a PCE.
The 6top interface document [I-D.ietf-6tisch-6top-interface]
specifies the generic data model that can be used to monitor and
manage resources of the 6top sublayer. Abstract methods are
suggested for use by a management entity in the device. The data
model also enables remote control operations on the 6top sublayer.
[I-D.ietf-6tisch-coap] defines an mapping of the 6top set of
commands, which is described in [I-D.ietf-6tisch-6top-interface], to
CoAP resources. This allows an entity to interact with the 6top
layer of a node that is multiple hops away in a RESTful fashion.
[I-D.ietf-6tisch-coap] also defines a basic set CoAP resources and
associated RESTful access methods (GET/PUT/POST/DELETE). The payload
(body) of the CoAP messages is encoded using the CBOR format. The
PCE commands are expected to be issued directly as CoAP requests or
to 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 interfaces that the 6TiSCH devices support.
This architecture will be refined to comply with DetNet
[I-D.finn-detnet-architecture] when the work is formalized.
5.3.4. Track Forwarding
By forwarding, this specification means the per-packet operation that
allows to deliver a packet to a next hop or an upper layer in this
node. Forwarding is based on pre-existing state that was installed
as a result of the routing computation of a Track by a PCE. The
6TiSCH architecture supports three different forwarding model, G-MPLS
Track Forwarding (TF), 6LoWPAN Fragment Forwarding (FF) and IPv6
Forwarding (6F) which is the classical IP operation. The DetNet case
relates to the Track Forwarding operation under the control of a PCE.
A Track is a unidirectional path between a source and a destination.
In a Track cell, the normal operation of IEEE802.15.4 Automatic
Repeat-reQuest (ARQ) usually happens, though the acknowledgment may
be omitted in some cases, for instance if there is no scheduled cell
for a retry.
Track Forwarding is the simplest and fastest. A bundle of cells set
to receive (RX-cells) is uniquely paired to a bundle of cells that
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are set to transmit (TX-cells), representing a layer-2 forwarding
state that can be used regardless of the network layer protocol.
This model can effectively be seen as a Generalized Multi-protocol
Label Switching (G-MPLS) operation in that the information used to
switch a frame is not an explicit label, but rather related to other
properties of the way the packet was received, a particular cell in
the case of 6TiSCH. As a result, as long as the TSCH MAC (and
Layer-2 security) accepts a frame, that frame can be switched
regardless of the protocol, whether this is an IPv6 packet, a 6LoWPAN
fragment, or a frame from an alternate protocol such as WirelessHART
or ISA100.11a.
A data frame that is forwarded along a Track normally has a
destination MAC address that is set to broadcast - or a multicast
address depending on MAC support. This way, the MAC layer in the
intermediate nodes accepts the incoming frame and 6top switches it
without incurring a change in the MAC header. In the case of
IEEE802.15.4, this means effectively broadcast, so that along the
Track the short address for the destination of the frame is set to
0xFFFF.
A Track is thus formed end-to-end as a succession of paired bundles,
a receive bundle from the previous hop and a transmit bundle to the
next hop along the Track, and a cell in such a bundle belongs to at
most one Track. For a given iteration of the device schedule, the
effective channel of the cell is obtained by adding a pseudo-random
number to the channelOffset of the cell, which results in a rotation
of the frequency that used for transmission. The bundles may be
computed so as to accommodate both variable rates and
retransmissions, so they might not be fully used at a given iteration
of the schedule. The 6TiSCH architecture provides additional means
to avoid waste of cells as well as overflows in the transmit bundle,
as follows:
In one hand, a TX-cell that is not needed for the current iteration
may be reused opportunistically on a per-hop basis for routed
packets. When all of the frame that were received for a given Track
are effectively transmitted, any available TX-cell for that Track can
be reused for upper layer traffic for which the next-hop router
matches the next hop along the Track. In that case, the cell that is
being used is effectively a TX-cell from the Track, but the short
address for the destination is that of the next-hop router. It
results that a frame that is received in a RX-cell of a Track with a
destination MAC address set to this node as opposed to broadcast must
be extracted from the Track and delivered to the upper layer (a frame
with an unrecognized MAC address is dropped at the lower MAC layer
and thus is not received at the 6top sublayer).
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On the other hand, it might happen that there are not enough TX-cells
in the transmit bundle to accommodate the Track traffic, for instance
if more retransmissions are needed than provisioned. In that case,
the frame can be placed for transmission in the bundle that is used
for layer-3 traffic towards the next hop along the track as long as
it can be routed by the upper layer, that is, typically, if the frame
transports an IPv6 packet. The MAC address should be set to the
next-hop MAC address to avoid confusion. It results that a frame
that is received over a layer-3 bundle may be in fact associated to a
Track. In a classical IP link such as an Ethernet, off-track traffic
is typically in excess over reservation to be routed along the non-
reserved path based on its QoS setting. But with 6TiSCH, since the
use of the layer-3 bundle may be due to transmission failures, it
makes sense for the receiver to recognize a frame that should be re-
tracked, and to place it back on the appropriate bundle if possible.
A frame should be re-tracked if the Per-Hop-Behavior group indicated
in the Differentiated Services Field in the IPv6 header is set to
Deterministic Forwarding, as discussed in Section 5.4.1. A frame is
re-tracked by scheduling it for transmission over the transmit bundle
associated to the Track, with the destination MAC address set to
broadcast.
There are 2 modes for a Track, transport mode and tunnel mode.
5.3.4.1. Transport Mode
In transport mode, the Protocol Data Unit (PDU) is associated with
flow-dependant meta-data that refers uniquely to the Track, so the
6top sublayer can place the frame in the appropriate cell without
ambiguity. In the case of IPv6 traffic, this flow identification is
transported in the Flow Label of the IPv6 header. Associated with
the source IPv6 address, the Flow Label forms a globally unique
identifier for that particular Track that is validated at egress
before restoring the destination MAC address (DMAC) and punting to
the upper layer.
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| ^
+--------------+ | |
| IPv6 | | |
+--------------+ | |
| 6LoWPAN HC | | |
+--------------+ ingress egress
| 6top | sets +----+ +----+ restores
+--------------+ dmac to | | | | dmac to
| TSCH MAC | brdcst | | | | self
+--------------+ | | | | | |
| LLN PHY | +-------+ +--...-----+ +-------+
+--------------+
Track Forwarding, Transport Mode
5.3.4.2. Tunnel Mode
In tunnel mode, the frames originate from an arbitrary protocol over
a compatible MAC that may or may not be synchronized with the 6TiSCH
network. An example of this would be a router with a dual radio that
is capable of receiving and sending WirelessHART or ISA100.11a frames
with the second radio, by presenting itself as an access Point or a
Backbone Router, respectively.
In that mode, some entity (e.g. PCE) can coordinate with a
WirelessHART Network Manager or an ISA100.11a System Manager to
specify the flows that are to be transported transparently over the
Track.
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+--------------+
| IPv6 |
+--------------+
| 6LoWPAN HC |
+--------------+ set restore
| 6top | +dmac+ +dmac+
+--------------+ to|brdcst to|nexthop
| TSCH MAC | | | | |
+--------------+ | | | |
| LLN PHY | +-------+ +--...-----+ +-------+
+--------------+ | ingress egress |
| |
+--------------+ | |
| LLN PHY | | |
+--------------+ | |
| TSCH MAC | | |
+--------------+ | dmac = | dmac =
|ISA100/WiHART | | nexthop v nexthop
+--------------+
Figure 7: Track Forwarding, Tunnel Mode
In that case, the flow information that identifies the Track at the
ingress 6TiSCH router is derived from the RX-cell. The dmac is set
to this node but the flow information indicates that the frame must
be tunneled over a particular Track so the frame is not passed to the
upper layer. Instead, the dmac is forced to broadcast and the frame
is passed to the 6top sublayer for switching.
At the egress 6TiSCH router, the reverse operation occurs. Based on
metadata associated to the Track, the frame is passed to the
appropriate link layer with the destination MAC restored.
5.3.4.3. Tunnel Metadata
Metadata coming with the Track configuration is expected to provide
the destination MAC address of the egress endpoint as well as the
tunnel mode and specific data depending on the mode, for instance a
service access point for frame delivery at egress. If the tunnel
egress point does not have a MAC address that matches the
configuration, the Track installation fails.
In transport mode, if the final layer-3 destination is the tunnel
termination, then it is possible that the IPv6 address of the
destination is compressed at the 6LoWPAN sublayer based on the MAC
address. It is thus mandatory at the ingress point to validate that
the MAC address that was used at the 6LoWPAN sublayer for compression
matches that of the tunnel egress point. For that reason, the node
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that injects a packet on a Track checks that the destination is
effectively that of the tunnel egress point before it overwrites it
to broadcast. The 6top sublayer at the tunnel egress point reverts
that operation to the MAC address obtained from the tunnel metadata.
5.4. Operations of Interest for DetNet and PCE
In a classical system, the 6TiSCH device does not place the request
for bandwidth between self and another device in the network.
Rather, an Operation Control System invoked through an Human/Machine
Interface (HMI) indicates the Traffic Specification, in particular in
terms of latency and reliability, and the end nodes. With this, the
PCE must compute a Track 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 to recognize when a certain packet
belongs to a certain Track, sort out duplicates, 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 Tracks. 6TiSCH expects that the programing of
the schedule will be done over COAP as discussed in 6TiSCH Resource
Management and Interaction using CoAP [I-D.ietf-6tisch-coap].
But an Hybrid mode may be required as well whereby a single Track is
added, modified, or removed, for instance if it appears that a Track
does not perform as expected for, say, PDR. For that case, the
expectation is that a protocol that flows along a Track (to be), in a
fashion similar to classical Traffic Engineering (TE) [CCAMP], may be
used to update the state in the devices. 6TiSCH provides means for a
device to negotiate a timeSlot with a neighbor, but in general that
flow was not designed and no protocol was selected and it is expected
that DetNet will determine the appropriate end-to-end protocols to be
used in that case.
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Stream Management Entity
Operational System and HMI
-+-+-+-+-+-+-+ Northbound -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
PCE PCE PCE PCE
-+-+-+-+-+-+-+ Southbound -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
--- 6TiSCH------6TiSCH------6TiSCH------6TiSCH--
6TiSCH / Device Device Device Device \
Device- - 6TiSCH
\ 6TiSCH 6TiSCH 6TiSCH 6TiSCH / Device
----Device------Device------Device------Device--
Figure 8
5.4.1. Packet Marking and Handling
Section "Packet Marking and Handling" of
[I-D.ietf-6tisch-architecture] describes the packet tagging and
marking that is expected in 6TiSCH networks.
5.4.1.1. Tagging Packets for Flow Identification
For packets that are routed by a PCE along a Track, the tuple formed
by the IPv6 source address and a local RPLInstanceID is tagged in the
packets to identify uniquely the Track and associated transmit bundle
of timeSlots.
It results that the tagging that is used for a DetNet flow outside
the 6TiSCH LLN MUST be swapped into 6TiSCH formats and back as the
packet enters and then leaves the 6TiSCH network.
Note: The method and format used for encoding the RPLInstanceID at
6lo is generalized to all 6TiSCH topological Instances, which
includes Tracks.
5.4.1.2. Replication, Retries and Elimination
6TiSCH expects elimination and replication of packets along a complex
Track, but has no position about how the sequence numbers would be
tagged in the packet.
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As it goes, 6TiSCH expects that timeSlots corresponding to copies of
a same packet along a Track are correlated by configuration, and does
not need to process the sequence numbers.
The semantics of the configuration MUST enable correlated timeSlots
to be grouped for transmit (and respectively receive) with a 'OR'
relations, and then a 'AND' relation MUST be configurable between
groups. The semantics is that if the transmit (and respectively
receive) operation succeeded in one timeSlot in a 'OR' group, then
all the other timeSLots in the group are ignored. Now, if there are
at least two groups, the 'AND' relation between the groups indicates
that one operation must succeed in each of the groups.
On the transmit side, timeSlots provisioned for retries along a same
branch of a Track are placed a same 'OR' group. The 'OR' relation
indicates that if a transmission is acknowledged, then further
transmissions SHOULD NOT be attempted for timeSlots in that group.
There are as many 'OR' groups as there are branches of the Track
departing from this node. Different 'OR' groups are programmed for
the purpose of replication, each group corresponding to one branch of
the Track. The 'AND' relation between the groups indicates that
transmission over any of branches MUST be attempted regardless of
whether a transmission succeeded in another branch. It is also
possible to place cells to different next-hop routers in a same 'OR'
group. This allows to route along multi-path tracks, trying one
next-hop and then another only if sending to the first fails.
On the receive side, all timeSlots are programmed in a same 'OR'
group. Retries of a same copy as well as converging branches for
elimination are converged, meaning that the first successful
reception is enough and that all the other timeSlots can be ignored.
5.4.1.3. Differentiated Services Per-Hop-Behavior
Additionally, an IP packet that is sent along a Track uses the
Differentiated Services Per-Hop-Behavior Group called Deterministic
Forwarding, as described in
[I-D.svshah-tsvwg-deterministic-forwarding].
5.4.2. Topology and capabilities
6TiSCH nodes are usually IoT devices, characterized by very limited
amount of memory, just enough buffers to store one or a few IPv6
packets, and limited bandwidth between peers. It results that a node
will maintain only a small number of peering information, and will
not be able to store many packets waiting to be forwarded. Peers can
be identified through MAC or IPv6 addresses, but a Cryptographically
Generated Address [RFC3972] (CGA) may also be used.
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Neighbors can be discovered over the radio using mechanism such as
beacons, but, though the neighbor information is available in the
6TiSCH interface data model, 6TiSCH does not describe a protocol to
pro-actively push the neighborhood information to a PCE. This
protocol should be described and should operate over CoAP. The
protocol should be able to carry multiple metrics, in particular the
same metrics as used for RPL operations [RFC6551]
The energy that the device consumes in sleep, transmit and receive
modes can be evaluated and reported. So can the amount of energy
that is stored in the device and the power that it can be scavenged
from the environment. The PCE SHOULD be able to compute Tracks that
will implement policies on how the energy is consumed, for instance
balance between nodes, ensure that the spent energy does not exceeded
the scavenged energy over a period of time, etc...
5.5. Security Considerations
On top of the classical protection of control signaling that can be
expected to support DetNet, it must be noted that 6TiSCH networks
operate on limited resources that can be depleted rapidly if an
attacker manages to operate a DoS attack on the system, for instance
by placing a rogue device in the network, or by obtaining management
control and to setup extra paths.
5.6. Acknowledgments
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.
6. Cellular Radio Use Cases
(This section was derived from draft-korhonen-detnet-telreq-00)
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6.1. Introduction and background
The recent developments in telecommunication networks, especially in
the cellular domain, are heading towards transport networks where
precise time synchronization support has to be one of the basic
building blocks. While the transport networks themselves have
practically transitioned to all-AP packet based networks to meet the
bandwidth and cost requirements, a highly accurate clock distribution
has become a challenge. Earlier the transport networks in the
cellular domain were typically time division and 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)
[SyncE] were used. 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. The time and
synchronization support are already topical for backhaul and midhaul
packet networks [MEF], and becoming a real issue for fronthaul
networks. Specifically in the fronthaul networks the timing and
synchronization requirements can be extreme for packet based
technologies, for example, in order of sub +-20 ns packet delay
variation (PDV) and frequency accuracy of +0.002 PPM [Fronthaul].
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 (RAN)
[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][I-D.mirsky-mpls-residence-time], these
solution are not necessarily sufficient for the forthcoming RAN
architectures or guarantee the higher time-synchronization
requirements [CPRI]. There are also existing solutions for the TDM
over IP [RFC5087] [RFC4553] or Ethernet transports [RFC5086]. The
really interesting and important existing 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. While IEEE 802.1AS
[IEEE8021AS] specifies a Layer-2 time synchronizing service other
specification, such as IEEE 1722 [IEEE1722] specify Ethernet-based
Layer-2 transport for time-sensitive streams. New promising work
seeks to enable the transport of time-sensitive fronthaul streams in
Ethernet bridged networks [IEEE8021CM]. Similarly to IEEE 1722 there
is an ongoing standardization effort to define Layer-2 transport
encapsulation format for transporting radio over Ethernet (RoE) in
IEEE 1904.3 Task Force [IEEE19043].
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As already mentioned all-IP RANs and various "haul" 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 and/or other tunneling protocols finally carrying
the Ethernet layer visible to the user plane IP traffic. While there
are existing technologies, especially in MPLS/PWE space, to establish
circuits through the routed and switched networks, there is a lack of
signaling the time synchronization and time-sensitive stream
requirements/reservations for Layer-3 flows in a way that the entire
transport stack is addressed and the Ethernet layers that needs to be
configured are addressed. Furthermore, not all "user plane" traffic
will be IP. Therefore, the same solution need also address the use
cases where the user plane traffic is again another layer or Ethernet
frames. There is existing work describing the problem statement
[I-D.finn-detnet-problem-statement] and the architecture
[I-D.finn-detnet-architecture] for deterministic networking (DetNet)
that eventually targets to provide solutions for time-sensitive (IP/
transport) streams with deterministic properties over Ethernet-based
switched networks.
This document describes requirements for deterministic networking in
a cellular telecom transport networks context. The requirements
include time synchronization, clock distribution and ways of
establishing time-sensitive streams for both Layer-2 and Layer-3 user
plane traffic using IETF protocol solutions.
The recent developments in telecommunication networks, especially in
the cellular domain, are heading towards transport networks where
precise time synchronization support has to be one of the basic
building blocks. While the transport networks themselves have
practically transitioned to all-AP packet based networks to meet the
bandwidth and cost requirements, a highly accurate clock distribution
has become a challenge. Earlier the transport networks in the
cellular domain were typically time division and 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)
[SyncE] were used. 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. The time and
synchronization support are already topical for backhaul and midhaul
packet networks [MEF], and becoming a real issue for fronthaul
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networks. Specifically in the fronthaul networks the timing and
synchronization requirements can be extreme for packet based
technologies, for example, in order of sub +-20 ns packet delay
variation (PDV) and frequency accuracy of +0.002 PPM [Fronthaul].
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 (RAN)
[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][I-D.mirsky-mpls-residence-time], these
solution are not necessarily sufficient for the forthcoming RAN
architectures or guarantee the higher time-synchronization
requirements [CPRI]. There are also existing solutions for the TDM
over IP [RFC5087] [RFC4553] or Ethernet transports [RFC5086]. The
really interesting and important existing 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. While IEEE 802.1AS
[IEEE8021AS] specifies a Layer-2 time synchronizing service other
specification, such as IEEE 1722 [IEEE1722] specify Ethernet-based
Layer-2 transport for time-sensitive streams. New promising work
seeks to enable the transport of time-sensitive fronthaul streams in
Ethernet bridged networks [IEEE8021CM]. Similarly to IEEE 1722 there
is an ongoing standardization effort to define Layer-2 transport
encapsulation format for transporting radio over Ethernet (RoE) in
IEEE 1904.3 Task Force [IEEE19043].
As already mentioned all-IP RANs and various "haul" 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 and/or other tunneling protocols finally carrying
the Ethernet layer visible to the user plane IP traffic. While there
are existing technologies, especially in MPLS/PWE space, to establish
circuits through the routed and switched networks, there is a lack of
signaling the time synchronization and time-sensitive stream
requirements/reservations for Layer-3 flows in a way that the entire
transport stack is addressed and the Ethernet layers that needs to be
configured are addressed. Furthermore, not all "user plane" traffic
will be IP. Therefore, the same solution need also address the use
cases where the user plane traffic is again another layer or Ethernet
frames. There is existing work describing the problem statement
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[I-D.finn-detnet-problem-statement] and the architecture
[I-D.finn-detnet-architecture] for deterministic networking (DetNet)
that eventually targets to provide solutions for time-sensitive (IP/
transport) streams with deterministic properties over Ethernet-based
switched networks.
This document describes requirements for deterministic networking in
a cellular telecom transport networks context. The requirements
include time synchronization, clock distribution and ways of
establishing time-sensitive streams for both Layer-2 and Layer-3 user
plane traffic using IETF protocol solutions.
6.2. Network architecture
Figure Figure 9 illustrates a typical, 3GPP defined, cellular network
architecture, which also has fronthaul and midhaul network segments.
The fronthaul refers to the network connecting base stations (base
band processing units) to the remote radio heads (antennas). The
midhaul network typically refers to the network inter-connecting base
stations (or small/pico cells).
Fronthaul networks build on the available excess time after the base
band processing of the radio frame has completed. Therefore, the
available time for networking is actually very limited, which in
practise determines how far the remote radio heads can be from the
base band processing units (i.e. base stations). For example, in a
case of LTE radio the Hybrid ARQ processing of a radio frame is
allocated 3 ms. Typically the processing completes way earlier (say
up to 400 us, could be much less, though) thus allowing the remaining
time to be used e.g. for fronthaul network. 200 us equals roughly 40
km of optical fiber based transport (assuming round trip time would
be total 2*200 us). The base band processing time and the available
"delay budget" for the fronthaul is a subject to change, possibly
dramatically, in the forthcoming "5G" to meet, for example, the
envisioned reduced radio round trip times, and other architecural and
service requirements [NGMN].
The maximum "delay budget" is then consumed by all nodes and required
buffering between the remote radio head and the base band processing
in addition to the distance incurred delay. Packet delay variation
(PDV) is problematic to fronthaul networks and must be minimized. If
the transport network cannot guarantee low enough PDV additional
buffering has to be introduced at the edges of the network to buffer
out the jitter. Any buffering will eat up the total available delay
budget, though. Section Section 6.3 will discuss the PDV
requirements in more detail.
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Y (remote radios)
\
Y__ \.--. .--. +------+
\_( `. +---+ _(Back`. | 3GPP |
Y------( Front )----|eNB|----( Haul )----| core |
( ` .Haul ) +---+ ( ` . ) ) | netw |
/`--(___.-' \ `--(___.-' +------+
Y_/ / \.--. \
Y_/ _( Mid`. \
( Haul ) \
( ` . ) ) \
`--(___.-'\_____+---+ (small cells)
\ |SCe|__Y
+---+ +---+
Y__|eNB|__Y
+---+
Y_/ \_Y ("local" radios)
Figure 9: Generic 3GPP-based cellular network architecture with
Front/Mid/Backhaul networks
6.3. Time synchronization requirements
Cellular networks starting from long term evolution (LTE) [TS36300]
[TS23401] radio the phase synchronization is also needed in addition
to the frequency synchronization. The commonly referenced fronthaul
network synchronization requirements are typically drawn from the
common public radio interface (CPRI) [CPRI] specification that
defines the transport protocol between the base band processing -
radio equipment controller (REC) and the remote antenna - radio
equipment (RE). However, the fundamental requirements still
originate from the respective cellular system and radio
specifications such as the 3GPP ones [TS25104][TS36104][TS36211]
[TS36133].
The fronthaul time synchronization requirements for the current 3GPP
LTE-based networks are listed below:
Transport link contribution to radio frequency error:
+-2 PPB. The given value is considered to be "available" for the
fronthaul link out of the total 50 PPB budget reserved for the
radio interface.
Delay accuracy:
+-8.138 ns i.e. +-1/32 Tc (UMTS Chip time, Tc, 1/3.84 MHz) to
downlink direction and excluding the (optical) cable length in one
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direction. Round trip accuracy is then +-16.276 ns. The value is
this low to meet the 3GPP timing alignment error (TAE) measurement
requirements.
Packet delay variation (PDV):
* 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.
The above listed time synchronization requirements are hard to meet
even with point to point connected networks, not to mention cases
where the underlying transport network actually constitutes of
multiple hops. It is expected that network deployments have to deal
with the jitter requirements buffering at the very ends of the
connections, 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 are valuable to make it easier
to meet the end to end requirements.
In order to meet the timing requirements both senders and receivers
must is perfect sync. This asks for a very accurate clock
distribution solution. Basically all means and hardware support for
guaranteeing accurate time synchronization in the network is needed.
As an example support for 1588 transparent clocks (TC) in every
intermediate node would be helpful.
6.4. Time-sensitive stream requirements
In addition to the time synchronization requirements listed in
Section Section 6.3 the fronthaul networks assume practically error
free transport. The maximum bit error rate (BER) has been defined to
be 10^-12. When packetized that would equal roughly to packet error
rate (PER) of 2.4*10^-9 (assuming ~300 bytes packets).
Retransmitting lost packets and/or using forward error coding (FEC)
to circumvent bit errors are practically impossible due additional
incurred delay. Using redundant streams for better guarantees for
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delivery is also practically impossible due to high bandwidth
requirements fronthaul networks have. For instance, current
uncompressed CPRI bandwidth expansion ratio is roughly 20:1 compared
to the IP layer user payload it carries in a "radio sample form".
The other fundamental assumption is that fronthaul links are
symmetric. Last, all fronthaul streams (carrying radio data) have
equal priority and cannot delay or pre-empt each other. This implies
the network has always be sufficiently under subscribed to guarantee
each time-sensitive flow meets their schedule.
Mapping the fronthaul requirements to [I-D.finn-detnet-architecture]
Section 3 "Providing the DetNet Quality of Service" what is seemed
usable are:
(a) Zero congestion loss.
(b) Pinned-down paths.
The current time-sensitive networking features may still not be
sufficient for fronthaul traffic. Therefore, having specific
profiles that take the requirements of fronthaul into account are
deemed to be useful [IEEE8021CM].
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 not limited to
solutions directly over Ethernet, over IP, and MPLS/PseudoWire
transport.
6.5. Security considerations
Establishing time-sensitive streams in the network entails reserving
networking resources sometimes for a considerable long time. It is
important that these reservation requests must be authenticated to
prevent malicious reservation attempts from hostile nodes or even
accidental misconfiguration. This is specifically important in a
case where the reservation requests span administrative domains.
Furthermore, the reservation information itself should be digitally
signed to reduce the risk where a legitimate node pushed a stale or
hostile configuration into the networking node.
7. Other Use Cases
(This section was derived from draft-zha-detnet-use-case-00)
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7.1. Introduction
The rapid growth of the today's communication system and its access
into almost all aspects of daily life has led to great dependency on
services it provides. The communication network, as it is today, has
applications such as multimedia and peer-to-peer file sharing
distribution that require Quality of Service (QoS) guarantees in
terms of delay and jitter to maintain a certain level of performance.
Meanwhile, mobile wireless communications has become an important
part to support modern sociality with increasing importance over the
last years. A communication network of hard real-time and high
reliability is essential for the next concurrent and next generation
mobile wireless networks as well as its bearer network for E-2-E
performance requirements.
Conventional transport network is IP-based because of the bandwidth
and cost requirements. However the delay and jitter guarantee
becomes a challenge in case of contention since the service here is
not deterministic but best effort. With more and more rigid demand
in latency control in the future network [METIS], deterministic
networking [I-D.finn-detnet-architecture] is a promising solution to
meet the ultra low delay applications and use cases. There are
already typical issues for delay sensitive networking requirements in
midhaul and backhaul network to support LTE and future 5G network
[net5G]. And not only in the telecom industry but also other
vertical industry has increasing demand on delay sensitive
communications as the automation becomes critical recently.
More specifically, CoMP techniques, D-2-D, industrial automation and
gaming/media service all have great dependency on the low delay
communications as well as high reliability to guarantee the service
performance. Note that the deterministic networking is not equal to
low latency as it is more focused on the worst case delay bound of
the duration of certain application or service. It can be argued
that without high certainty and absolute delay guarantee, low delay
provisioning is just relative [rfc3393], which is not sufficient to
some delay critical service since delay violation in an instance
cannot be tolerated. Overall, the requirements from vertical
industries seem to be well aligned with the expected low latency and
high determinist performance of future networks
This document describes several use cases and scenarios with
requirements on deterministic delay guarantee within the scope of the
deterministic network [I-D.finn-detnet-problem-statement].
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7.2. Critical Delay Requirements
Delay and jitter requirement has been take into account as a major
component in QoS provisioning since the birth of Internet. The delay
sensitive networking with increasing importance become the root of
mobile wireless communications as well as the applicable areas which
are all greatly relied on low delay communications. Due to the best
effort feature of the IP networking, mitigate contention and
buffering is the main solution to serve the delay sensitive service.
More bandwidth is assigned to keep the link low loaded or in another
word, reduce the probability of congestion. However, not only lack
of determinist but also has limitation to serve the applications in
the future communication system, keeping low loaded cannot provide
deterministic delay guarantee. Take the [METIS] that documents the
fundamental challenges as well as overall technical goal of the 5G
mobile and wireless system as the starting point. It should
supports: -1000 times higher mobile data volume per area, -10 times
to 100 times higher typical user data rate, -10 times to 100 times
higher number of connected devices, -10 times longer battery life for
low power devices, and -5 times reduced End-to-End (E2E) latency, at
similar cost and energy consumption levels as today's system. Taking
part of these requirements related to latency, current LTE networking
system has E2E latency less than 20ms [LTE-Latency] which leads to
around 5ms E2E latency for 5G networks. It has been argued that
fulfill such rigid latency demand with similar cost will be most
challenging as the system also requires 100 times bandwidth as well
as 100 times of connected devices. As a result to that, simply
adding redundant bandwidth provisioning can be no longer an efficient
solution due to the high bandwidth requirements more than ever
before. In addition to the bandwidth provisioning, the critical flow
within its reserved resource should not be affected by other flows no
matter the pressure of the network. Robust defense of critical flow
is also not depended on redundant bandwidth allocation.
Deterministic networking techniques in both layer-2 and layer-3 using
IETF protocol solutions can be promising to serve these scenarios.
7.3. Coordinated multipoint processing (CoMP)
In the wireless communication system, Coordinated multipoint
processing (CoMP) is considered as an effective technique to solve
the inter-cell interference problem to improve the cell-edge user
throughput [CoMP].
7.3.1. CoMP Architecture
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+--------------------------+
| CoMP |
+--+--------------------+--+
| |
+----------+ +------------+
| Uplink | | Downlink |
+-----+----+ +--------+---+
| |
------------------- -----------------------
| | | | | |
+---------+ +----+ +-----+ +------------+ +-----+ +-----+
| Joint | | CS | | DPS | | Joint | | CS/ | | DPS |
|Reception| | | | | |Transmission| | CB | | |
+---------+ +----+ +-----+ +------------+ +-----+ +-----+
| |
|----------- |-------------
| | | |
+------------+ +---------+ +----------+ +------------+
| Joint | | Soft | | Coherent | | Non- |
|Equalization| |Combining| | JT | | Coherent JT|
+------------+ +---------+ +----------+ +------------+
Figure 10: Framework of CoMP Technology
As shown in Figure 10, CoMP reception and transmission is a framework
that multiple geographically distributed antenna nodes cooperate to
improve the performance of the users served in the common cooperation
area. The design principal of CoMP is to extend the current single-
cell to multi-UEs transmission to a multi-cell- to-multi-UEs
transmission by base station cooperation. In contrast to single-cell
scenario, CoMP has critical issues such as: Backhaul latency, CSI
(Channel State Information) reporting and accuracy and Network
complexity. Clearly the first two requirements are very much delay
sensitive and will be discussed in next section.
7.3.2. Delay Sensitivity in CoMP
As the essential feature of CoMP, signaling is exchanged between
eNBs, the backhaul latency is the dominating limitation of the CoMP
performance. Generally, JT and JP may benefit from coordinating the
scheduling (distributed or centralized) of different cells in case
that the signaling exchanging between eNBs is limited to 4-10ms. For
C-RAN the backhaul latency requirement is 250us while for D-RAN it is
4-15ms. And this delay requirement is not only rigid but also
absolute since any uncertainty in delay will down the performance
significantly. Note that, some operator's transport network is not
build to support Layer-3 transfer in aggregation layer. In such
case, the signaling is exchanged through EPC which means delay is
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supposed to be larger. CoMP has high requirement on delay and
reliability which is lack by current mobile network systems and may
impact the architecture of the mobile network.
7.4. Industrial Automation
Traditional "industrial automation" terminology usually refers to
automation of manufacturing, quality control and material processing.
"Industrial internet" and "industrial 4.0" [EA12] is becoming a hot
topic based on the Internet of Things. This high flexible and
dynamic engineering and manufacturing will result in a lot of so-
called smart approaches such as Smart Factory, Smart Products, Smart
Mobility, and Smart Home/Buildings. No doubt that ultra high
reliability and robustness is a must in data transmission, especially
in the closed loop automation control application where delay
requirement is below 1ms and packet loss less than 10E-9. All these
critical requirements on both latency and loss cannot be fulfilled by
current 4G communication networks. Moreover, the collaboration of
the industrial automation from remote campus with cellular and fixed
network has to be built on an integrated, cloud-based platform. In
this way, the deterministic flows should be guaranteed regardless of
the amount of other flows in the network. The lack of this mechanism
becomes the main obstacle in deployment on of industrial automation.
7.5. Vehicle to Vehicle
V2V communication has gained more and more attention in the last few
years and will be increasingly growth in the future. Not only
equipped with direct communication system which is short ranged, V2V
communication also requires wireless cellular networks to cover wide
range and more sophisticated services. V2V application in the area
autonomous driving has very stringent requirements of latency and
reliability. It is critical that the timely arrival of information
for safety issues. In addition, due to the limitation of processing
of individual vehicle, passing information to the cloud can provide
more functions such as video processing, audio recognition or
navigation systems. All of those requirements lead to a highly
reliable connectivity to the cloud. On the other hand, it is natural
that the provisioning of low latency communication is one of the main
challenges to be overcome as a result of the high mobility, the high
penetration losses caused by the vehicle itself. As result of that,
the data transmission with latency below 5ms and a high reliability
of PER below 10E-6 are demanded. It can benefit from the deployment
of deterministic networking with high reliability.
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7.6. Gaming, Media and Virtual Reality
Online gaming and cloud gaming is dominating the gaming market since
it allow multiple players to play together with more challenging and
competing. Connected via current internet, the latency can be a big
issue to degrade the end users' experience. There different types of
games and FPS (First Person Shooting) gaming has been considered to
be the most latency sensitive online gaming due to the high
requirements of timing precision and computing of moving target.
Virtual reality is also receiving more interests than ever before as
a novel gaming experience. The delay here can be very critical to
the interacting in the virtual world. Disagreement between what is
seeing and what is feeling can cause motion sickness and affect what
happens in the game. Supporting fast, real-time and reliable
communications in both PHY/MAC layer, network layer and application
layer is main bottleneck for such use case. The media content
delivery has been and will become even more important use of
Internet. Not only high bandwidth demand but also critical delay and
jitter requirements have to be taken into account to meet the user
demand. To make the smoothness of the video and audio, delay and
jitter has to be guaranteed to avoid possible interruption which is
the killer of all online media on demand service. Now with 4K and 8K
video in the near future, the delay guarantee become one of the most
challenging issue than ever before. 4K/8K UHD video service requires
6Gbps-100Gbps for uncompressed video and compressed video starting
from 60Mbps. The delay requirement is 100ms while some specific
interactive applications may require 10ms delay [UHD-video].
8. Use Case Common Elements
Looking at the use cases collectively, the following common desires
for the DetNet-based networks of the future emerge:
o Open standards-based network (replace various proprietary
networks, reduce cost, create multi-vendor market)
o Centrally administered (though such administration may be
distributed for scale and resiliency)
o Integrates L2 (bridged) and L3 (routed) environments (independent
of the Link layer, e.g. can be used with Ethernet, 6TiSCH, etc.)
o Carries both deterministic and best-effort traffic (guaranteed
end-to-end delivery of deterministic flows, deterministic flows
isolated from each other and from best-effort traffic congestion,
unused deterministic BW available to best-effort traffic)
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o Ability to add or remove systems from the network with minimal,
bounded service interruption (applications include replacement of
failed devices as well as plug and play)
o Uses standardized data flow information models capable of
expressing deterministic properties (models express device
capabilities, flow properties. Protocols for pushing models from
controller to devices, devices to controller)
o Scalable size (long distances (many km) and short distances
(within a single machine), many hops (radio repeaters, microwave
links, fiber links...) and short hops (single machine))
o Scalable timing parameters and accuracy (bounded latency,
guaranteed worst case maximum, minimum. Low latency, e.g. control
loops may be less than 1ms, but larger for wide area networks)
o High availability (99.9999 percent up time requested, but may be
up to twelve 9s)
o Reliability, redundancy (lives at stake)
o Security (from failures, attackers, misbehaving devices -
sensitive to both packet content and arrival time)
9. Acknowledgments
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.
10. Informative References
[ACE] IETF, "Authentication and Authorization for Constrained
Environments", <https://datatracker.ietf.org/doc/charter-
ietf-ace/>.
[bacnetip]
ASHRAE, "Annex J to ANSI/ASHRAE 135-1995 - BACnet/IP",
January 1999.
[CCAMP] IETF, "Common Control and Measurement Plane",
<https://datatracker.ietf.org/doc/charter-ietf-ccamp/>.
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[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>.
[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/>.
[DICE] IETF, "DTLS In Constrained Environments",
<https://datatracker.ietf.org/doc/charter-ietf-dice/>.
[EA12] Evans, P. and M. Annunziata, "Industrial Internet: Pushing
the Boundaries of Minds and Machines", November 2012.
[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>.
[HART] www.hartcomm.org, "Highway Addressable remote Transducer,
a group of specifications for industrial process and
control devices administered by the HART Foundation".
[I-D.finn-detnet-architecture]
Finn, N., Thubert, P., and M. Teener, "Deterministic
Networking Architecture", draft-finn-detnet-
architecture-02 (work in progress), November 2015.
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[I-D.finn-detnet-problem-statement]
Finn, N. and P. Thubert, "Deterministic Networking Problem
Statement", draft-finn-detnet-problem-statement-04 (work
in progress), October 2015.
[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-08 (work
in progress), May 2015.
[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.
[I-D.ietf-6tisch-terminology]
Palattella, M., Thubert, P., Watteyne, T., and Q. Wang,
"Terminology in IPv6 over the TSCH mode of IEEE
802.15.4e", draft-ietf-6tisch-terminology-06 (work in
progress), November 2015.
[I-D.ietf-ipv6-multilink-subnets]
Thaler, D. and C. Huitema, "Multi-link Subnet Support in
IPv6", draft-ietf-ipv6-multilink-subnets-00 (work in
progress), July 2002.
[I-D.ietf-roll-rpl-industrial-applicability]
Phinney, T., Thubert, P., and R. Assimiti, "RPL
applicability in industrial networks", draft-ietf-roll-
rpl-industrial-applicability-02 (work in progress),
October 2013.
[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.
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[I-D.mirsky-mpls-residence-time]
Mirsky, G., Ruffini, S., Gray, E., Drake, J., Bryant, S.,
and S. Vainshtein, "Residence Time Measurement in MPLS
network", draft-mirsky-mpls-residence-time-07 (work in
progress), July 2015.
[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.thubert-6lowpan-backbone-router]
Thubert, P., "6LoWPAN Backbone Router", draft-thubert-
6lowpan-backbone-router-03 (work in progress), February
2013.
[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.
[IEC61850-90-12]
TC57 WG10, IEC., "IEC 61850-90-12 TR: Communication
networks and systems for power utility automation - Part
90-12: Wide area network engineering guidelines", 2015.
[IEC62439-3:2012]
TC65, IEC., "IEC 62439-3: Industrial communication
networks - High availability automation networks - Part 3:
Parallel Redundancy Protocol (PRP) and High-availability
Seamless Redundancy (HSR)", 2012.
[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>.
[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>.
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[IEEE19043]
IEEE Standards Association, "IEEE 1904.3 TF", IEEE 1904.3,
2015, <http://www.ieee1904.org/3/tf3_home.shtml>.
[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.
[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/>.
[ISA100.11a]
ISA/ANSI, "Wireless Systems for Industrial Automation:
Process Control and Related Applications - ISA100.11a-2011
- IEC 62734", 2011, <http://www.isa.org/Community/
SP100WirelessSystemsforAutomation>.
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[ISO7240-16]
ISO, "ISO 7240-16:2007 Fire detection and alarm systems --
Part 16: Sound system control and indicating equipment",
2007, <http://www.iso.org/iso/
catalogue_detail.htm?csnumber=42978>.
[knx] KNX Association, "ISO/IEC 14543-3 - KNX", November 2006.
[lontalk] ECHELON, "LonTalk(R) Protocol Specification Version 3.0",
1994.
[LTE-Latency]
Johnston, S., "LTE Latency: How does it compare to other
technologies", March 2014,
<http://opensignal.com/blog/2014/03/10/
lte-latency-how-does-it-compare-to-other-technologies>.
[MEF] 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>.
[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.
[net5G] Ericsson, "5G Radio Access, Challenges for 2020 and
Beyond", Ericsson white paper wp-5g, June 2013,
<http://www.ericsson.com/res/docs/whitepapers/wp-5g.pdf>.
[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>.
[PCE] IETF, "Path Computation Element",
<https://datatracker.ietf.org/doc/charter-ietf-pce/>.
[profibus]
IEC, "IEC 61158 Type 3 - Profibus DP", January 2001.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
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[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
December 1998, <http://www.rfc-editor.org/info/rfc2460>.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474, DOI
10.17487/RFC2474, December 1998,
<http://www.rfc-editor.org/info/rfc2474>.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031, DOI 10.17487/
RFC3031, January 2001,
<http://www.rfc-editor.org/info/rfc3031>.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
<http://www.rfc-editor.org/info/rfc3209>.
[RFC3393] Demichelis, C. and P. Chimento, "IP Packet Delay Variation
Metric for IP Performance Metrics (IPPM)", RFC 3393, DOI
10.17487/RFC3393, November 2002,
<http://www.rfc-editor.org/info/rfc3393>.
[RFC3444] Pras, A. and J. Schoenwaelder, "On the Difference between
Information Models and Data Models", RFC 3444, DOI
10.17487/RFC3444, January 2003,
<http://www.rfc-editor.org/info/rfc3444>.
[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, DOI 10.17487/RFC3972, March 2005,
<http://www.rfc-editor.org/info/rfc3972>.
[RFC3985] Bryant, S., Ed. and P. Pate, Ed., "Pseudo Wire Emulation
Edge-to-Edge (PWE3) Architecture", RFC 3985, DOI 10.17487/
RFC3985, March 2005,
<http://www.rfc-editor.org/info/rfc3985>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <http://www.rfc-editor.org/info/rfc4291>.
[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,
<http://www.rfc-editor.org/info/rfc4553>.
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[RFC4903] Thaler, D., "Multi-Link Subnet Issues", RFC 4903, DOI
10.17487/RFC4903, June 2007,
<http://www.rfc-editor.org/info/rfc4903>.
[RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6
over Low-Power Wireless Personal Area Networks (6LoWPANs):
Overview, Assumptions, Problem Statement, and Goals", RFC
4919, DOI 10.17487/RFC4919, August 2007,
<http://www.rfc-editor.org/info/rfc4919>.
[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,
<http://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,
<http://www.rfc-editor.org/info/rfc5087>.
[RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
DOI 10.17487/RFC6282, September 2011,
<http://www.rfc-editor.org/info/rfc6282>.
[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,
<http://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,
<http://www.rfc-editor.org/info/rfc6551>.
[RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C.
Bormann, "Neighbor Discovery Optimization for IPv6 over
Low-Power Wireless Personal Area Networks (6LoWPANs)", RFC
6775, DOI 10.17487/RFC6775, November 2012,
<http://www.rfc-editor.org/info/rfc6775>.
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[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,
<http://www.rfc-editor.org/info/rfc7554>.
[SRP_LATENCY]
Gunther, C., "Specifying SRP Latency", 2014,
<http://www.ieee802.org/1/files/public/docs2014/
cc-cgunther-acceptable-latency-0314-v01.pdf>.
[STUDIO_IP]
Mace, G., "IP Networked Studio Infrastructure for
Synchronized & Real-Time Multimedia Transmissions", 2007,
<http://www.ieee802.org/1/files/public/docs2047/
avb-mace-ip-networked-studio-infrastructure-0107.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>.
[TEAS] IETF, "Traffic Engineering Architecture and Signaling",
<https://datatracker.ietf.org/doc/charter-ietf-teas/>.
[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.
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[TSNTG] IEEE Standards Association, "IEEE 802.1 Time-Sensitive
Networks Task Group", 2013,
<http://www.IEEE802.org/1/pages/avbridges.html>.
[UHD-video]
Holub, P., "Ultra-High Definition Videos and Their
Applications over the Network", The 7th International
Symposium on VICTORIES Project PetrHolub_presentation,
October 2014, <http://www.aist-
victories.org/jp/7th_sympo_ws/PetrHolub_presentation.pdf>.
[WirelessHART]
www.hartcomm.org, "Industrial Communication Networks -
Wireless Communication Network and Communication Profiles
- WirelessHART - IEC 62591", 2010.
Authors' Addresses
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
Craig Gunther
Harman International
10653 South River Front Parkway
South Jordan, UT 84095
USA
Phone: +1 801 568-7675
Email: craig.gunther@harman.com
URI: http://www.harman.com
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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, CA 95134
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
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Subir Das
Applied Communication Sciences
150 Mount Airy Road, Basking Ridge
New Jersey, 07920, USA
Email: sdas@appcomsci.com
Yiyong Zha
Huawei Technologies
Email: zhayiyong@huawei.com
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