Internet DRAFT - draft-xiong-detnet-wide-area-ip-requirements
draft-xiong-detnet-wide-area-ip-requirements
DETNET Q. Xiong
Internet-Draft ZTE Corporation
Intended status: Standards Track October 2021
Expires: 27 April 2022
The Requirements for Wide-area IP Deterministic Networking
draft-xiong-detnet-wide-area-ip-requirements-00
Abstract
In wide-area IP networks, more requirements need to be taken into
considerations such as differentiated DetNet QoS of multiple
services, high-efficiency of resources utilization and routes
steering, integration of large-scale heterogeneous network and
guarantees of multiple dynamic deterministic flows. This document
describes the requirements in wide-area applications and proposes the
solution with deterministic resources, routes and QoS.
Status of This Memo
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Copyright (c) 2021 IETF Trust and the persons identified as the
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 4
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Requirements Language . . . . . . . . . . . . . . . . . . 4
3. Requirements for Wide-area IP Deterministic Networking . . . 4
3.1. Differentiated DetNet QoS of Multiple Services . . . . . 4
3.2. Integration of Large-scale Heterogeneous Network . . . . 5
3.3. Efficiency of Resources Utilization and Routes
Steering . . . . . . . . . . . . . . . . . . . . . . . . 6
3.4. Guarantees of Multiple Dynamic Deterministic Flows . . . 6
4. Solutions Considerations of Wide-area IP Deterministic
Networking . . . . . . . . . . . . . . . . . . . . . . . 7
4.1. The Deterministic Resources . . . . . . . . . . . . . . . 7
4.2. The Deterministic Routes . . . . . . . . . . . . . . . . 7
4.3. The Deterministic QoS . . . . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8. Normative References . . . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
5G network is oriented to the internet of everything. In addition to
the Enhanced Mobile Broadband (eMBB) and Massive Machine Type
Communications(mMTC) services, it also supports the Ultra-reliable
Low Latency Communications (uRLLC) services. The uRLLC services
cover the industries such as intelligent electrical network,
intelligent factory, internet of vehicles, industry automation and
other industrial internet scenarios, which is the key demand of
digital transformation of vertical domains. These uRLLC services
demand SLA guarantees such as low latency and high reliability and
other deterministic and precise properties.
For the intelligent electrical network, there are deterministic
requirements for communication delay, jitter and packet loss rate.
For example, in the electrical current difference model, a delay of
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3~10ms and a jitter variation is no more than 100us are required.
The isolation requirement is also important. For example, the
automatic operation, control of a process, isochronous data and low
priority service need to meet the requirements of hard isolation. In
addition to the requirements of delay and jitter, the differential
protection (DP) service needs to be isolated from other services.
The industrial internet is the key infrastructure that coordinate
various units of work over various system components, e.g. people,
machines and things in the industrial environment including big data,
cloud computing, Internet of Things (IOT), Augment Reality (AR),
industrial robots, Artificial Intelligence (AI) and other basic
technologies. For example, automation control is one of the basic
application and the the core is closed-loop control system. The
control process cycle is as low as millisecond level, so the system
communication delay needs to reach millisecond level or even lower to
ensure the realization of precise control. There are three levels of
real-time requirements for industrial interconnection: factory level
is about 1s, and process level is 10~100ms, and the highest real-time
requirement is motion control, which requires less than 1ms.
The applications in 5G networks demand much more deterministic and
precise properties. But traditional Ethernet, IP and MPLS networks
which is based on statistical multiplexing provides best-effort
packet service and offers no delivery and SLA guarantee. The
deterministic forwarding can only apply to flows with such well-
defined characteristics as periodicity and burstiness. Technologies
to provide deterministic service has been proposed to provide bounded
latency and jitter based on a best-effort packet network. IEEE 802.1
Time-Sensitive Networking (TSN) has been proposed to provide bounded
latency and jitter in L2 LAN networks. According to [RFC8655],
Deterministic Networking (DetNet) operates at the IP layer and
delivers service which provides extremely low data loss rates and
bounded latency within a network domain.
The deterministic networks not only need to offer the Service Level
Agreements (SLA) guarantees such as low latency and jitter, low
packet loss and high reliability, but also need to support the
precise services such as flexible resource allocation and service
isolation. However, under the existing IP network architecture with
statistical multiplexing characteristics, the existing deterministic
technologies are facing large scale number of nodes and long-distance
transmission, traffic scheduling, dynamic flows, and other
controversial issues especially in Wide Area Network (WAN)
applications.
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In wide-area IP networks, more requirements need to be taken into
considerations such as differentiated DetNet QoS of multiple
services, high-efficiency of resources utilization and routes
steering, integration of large-scale heterogeneous network and
guarantees of multiple dynamic deterministic flows. This document
describes the requirements in wide-area applications and proposes the
solution with deterministic resources, routes and QoS.
2. Conventions used in this document
2.1. Terminology
The terminology is defined as [RFC8655].
2.2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Requirements for Wide-area IP Deterministic Networking
3.1. Differentiated DetNet QoS of Multiple Services
As defined in [RFC8655], the DetNet QoS can be expressed in terms of
: Minimum and maximum end-to-end latency, bounded jitter (packet
delay variation), packet loss ratio and an upper bound on out-of-
order packet delivery. As described in [RFC8578], DetNet
applications differ in their network topologies and specific desired
behavior and different services requires differentiated DetNet QoS.
In the WAN scenarios, multiple services with differentiated DetNet
QoS is co-existed in the same DetNet network. The classification of
the deterministic flows is should be taken into considerations. It
is required to provide Latency, bounded jitter and packet loss
dynamically and flexibly in all scenarios for each characterizd flow.
As the Figure 1 shown, the services is divided into 4 levels and
level 1~3 is the DetNet flows and level-4 is non-DetNet flow. DetNet
applications and DetNet QoS is differentiated within each level.
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+--------------+---------------+------------+-----------+-----------+
| Item | Level-1 | Level-2 | Level-3 | Level-4 |
+--------------+---------------+------------+-----------+-----------+
| Applications | Industrial | VR/AR | Audio and | Broadcast |
| Examples | | | Video | |
+--------------+---------------+------------+-----------+-----------+
| DetNet QoS | Ultra-low | Low | Low | Best |
| | latency and | latency | latency | Effort |
| | jitter | and jitter | | |
+--------------+---------------+------------+-----------+-----------+
Figure 1: Figure 1: The classification of multiple services
Moreover, different DetNet services is required to tolerate different
percentage of packet loss ratio such as 99.9%, 99.99%, 99.999%, and
so on. It is also required to provide service isolation. In some
scenarios, such as intelligent electrical network, the isolation
requirements are very important. For example, the automatic
operation or control of a process or isochronous data and service
with different priorities need to meet the requirements of hard
isolation. In addition to the requirements of delay and jitter, the
differential protection (DP) service needs to be isolated from other
services and hard isolated tunnel is required.
3.2. Integration of Large-scale Heterogeneous Network
In WAN application, large-scale number of nodes and long-distance
transmission in the network will lead to latency and jitter, such as
increasing transmission latency, jitter and packet loss. It is to
required reduce the scale of the network topology by establishing
cutthrough channels. The existing technologies such as FlexE and SR
tunnels should be taken into consideration. And multiple
capabilities is also provided by the nodes and links within the
network topology such as FlexE tunnels, TSN sub-network and IP/MPLS/
SRv6 tunnels. It is required to integrate the multi-capability
resources to achieve the optimal DetNet QoS.
Another option is to divide the network into several domains and
segments. And the deadline of latency and jitter of each domain and
segment should be determined and controlled. It is required to
control the DetNet QoS at the inter-domain boundary nodes and achieve
the end-to-end latency, bounded jitter and packet loss ratio across.
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3.3. Efficiency of Resources Utilization and Routes Steering
Traditional Ethernet, IP and MPLS networks which is based on
statistical multiplexing provides best-effort packet service and
offers no delivery and SLA guarantee. As described in [RFC8655], the
primary technique by which DetNet achieves its QoS is to allocate
sufficient resources. But it can not be achieved by not sufficient
resource which can be allocated due to practical and cost reason. So
it is required to achieve the high-efficiency of resources
utilization when provide the DetNet service.
Network resources include nodes, links, ports, bandwidth, queues,
etc. The congestion control, shaping and queue scheduling and other
traffic mechanisms which have been proposed in IEEE 802.1 TSN such as
IEEE802.1Qbv, IEEE802.1Qch, IEEE802.1Qav, IEEE802.1Qcr and so on.
Heterogeneous resource should be used and unified and simplified
resources mechanism under the selection of existing multiple
technical methods to realize the elastic of deterministic capability.
Resource classification and modeling is required along with the
explicit path with more SLA guarantee parameters like bandwidth,
latency, jitter, packet loss and so on. On the basic of the
resources, the steering path and routes for deterministic flows
should be programmed before the flows coming and able to provide SLA
capability. And the routes should be considered to be established in
distributed and centralized control Plane.
3.4. Guarantees of Multiple Dynamic Deterministic Flows
As described in [RFC8557], deterministic forwarding can only apply to
flows with such well-defined characteristics as periodicity and
burstiness. As defined in DetNet architecture [RFC8655], the traffic
characteristics of an App-flow can be CBR (constant bit rate) or VBR
(variable bit rate) of L1, L2 and L3 layers (VBR takes the maximum
value when reserving resources). But the current scenarios and
technical solutions only consider CBR flow, without considering the
coexistence of VBR and CBR, the burst and aperiodicity of flows. The
operations such as shaping or scheduling have not been specified.
Even TSN mechanisms are based on a constant and forecastable traffic
characteristics.
It will be more complicated in WAN applications where much more flows
coexist and the traffic characteristics is more dynamic. It is
required to offer reliable delivery and SLA guarantee for dynamic
flows. For example, periodic flow and aperiodic flow (including
micro burst flow, etc.), CBR and VBR flow, flow with different
periods or phases, etc. When the network needs to forward these
deterministic flows at the same time, it must solve the problems of
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time window selection, queue processing and aggregation of multiple
flows. It is required to classify the dynamic deterministic flows
and map them into different virtual topologies to limit the number of
the concurrent flows and reduce the micro bursts.
4. Solutions Considerations of Wide-area IP Deterministic Networking
4.1. The Deterministic Resources
As defined in RFC8655, the resource allocation is one of the
techniques to achieve the DetNet QoS. Network resources include
nodes, links, ports, bandwidth, queues, etc. The deterministic
resources require planning and arrangement of network resources,
resources modeling, resource allocation and reservation, resource
isolation and resource scheduling, etc. In order to meet the
requirements of deterministic service, resources need to be
classified, including ultra-low delay resources, low delay resources,
low jitter resources, etc.
Deterministic resources guarantee the delay, jitter and other
requirements of deterministic services by reserving resources for
flows. If the network resources are sufficient, congestion and
packet loss can be eliminated to meet the requirements of low delay
jitter. If the network resources are insufficient, congestion
control, queue mechanisms of deterministic flows need to be carried
out. The nodes with different queue mechanisms provide different
latency and bounded jitter. Moreover, network resources could to be
reconstructed to provide ultra-low latency, for example, L1 layer
resources could be used to provide cutthrough channels, FlexE pipes,
etc.
4.2. The Deterministic Routes
The deterministic routes is based on the provision of deterministic
resources. The deterministic routes refers to the requirements to
select the network routes for the deterministic flows to guarantee
the stability of the routing at least during the packets
transmission, and the path will not change within the real-time
change of network topology. Moreover, the deterministic routes
should provide the capability including the latency, jitter and
packet loss ratio.
Routes generally perform forwarding function including receiving the
incoming packets and forwarding the packets to a Router based on the
header information and a forwarding information base. It is
necessary to provide pre-routes with SLA capability and generate
endogenous deterministic routing with deterministic capability. The
deterministic routes perform the functions of forwarding and QoS
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guarantee at the same time. The types of deterministic routes can be
classified into ultra-low delay routes, low delay routes, low jitter
routes, and so on. There can also has replication routes and
aggregation routes.
The mechanisms of path establishment include traffic engineering
technology (MPLS-TE, SR-TE, static configuration, etc.), IGP
technology, etc. Explicit strict routing can guarantee the delay
jitter and other requirements of services. Loose routing only
generates some endogenous deterministic routes, and other routes
still need forwarding and scheduling, such as dynamic resource-aware
routing and queue scheduling.
4.3. The Deterministic QoS
The deterministic QoS is to arrange and schedule the deterministic
flows on the basis of providing deterministic resources and routes,
so as to control of each flow and meet the DetNet QoS goals.
The scheduling and control include the classification of the
deterministic flows, queue scheduling mechanism for each class of
deterministic flow, deterministic shaping at boundary nodes, limiting
the number of concurrent flows and reducing micro bursts, mapping the
dynamic concurrent flows into different virtual topologies.
Moreover, flow aggregation is performed at the aggregation node to
reduce flow state maintenance and replication or elimination is
performed at the relay node to achieve reliability.
If the deterministic flows crosses multiple domains, the end-to-end
latency is the sum of delay from all domains. It is required to
control the deadline delay of each domain. Moreover, bounded jitter
(packet delay variation) should be adjusted and scheduled at the
inter-domain boundary nodes.
5. Security Considerations
TBA
6. Acknowledgements
TBA
7. IANA Considerations
TBA
8. Normative References
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8557] Finn, N. and P. Thubert, "Deterministic Networking Problem
Statement", RFC 8557, DOI 10.17487/RFC8557, May 2019,
<https://www.rfc-editor.org/info/rfc8557>.
[RFC8578] Grossman, E., Ed., "Deterministic Networking Use Cases",
RFC 8578, DOI 10.17487/RFC8578, May 2019,
<https://www.rfc-editor.org/info/rfc8578>.
[RFC8655] Finn, N., Thubert, P., Varga, B., and J. Farkas,
"Deterministic Networking Architecture", RFC 8655,
DOI 10.17487/RFC8655, October 2019,
<https://www.rfc-editor.org/info/rfc8655>.
Author's Address
Quan Xiong
ZTE Corporation
No.6 Huashi Park Rd
Wuhan
Hubei, 430223
China
Email: xiong.quan@zte.com.cn
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