Internet DRAFT - draft-xiong-rtgwg-precise-tn-problem-statement
draft-xiong-rtgwg-precise-tn-problem-statement
RTGWG Q. Xiong
Internet-Draft ZTE Corporation
Intended status: Standards Track P. Liu
Expires: May 5, 2021 China Mobile
November 1, 2020
The Problem Statement for Precise Transport Networking
draft-xiong-rtgwg-precise-tn-problem-statement-01
Abstract
As described in [I-D.xiong-rtgwg-precise-tn-requirements], 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 so as to the Precise Transport Networking. However, under
the existing IP network architecture with statistical multiplexing
characteristics, the existing deterministic technologies are facing
long-distance transmission, queue scheduling, dynamic flows and per-
flow state maintenance and other controversial issues especially in
Wide Area Network (WAN) applications.
This document analyses the problems in existing deterministic
technologies to provide precise services in various industries such
as 5G networks.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 5, 2021.
Xiong & Liu Expires May 5, 2021 [Page 1]
Internet-DraftThe Problem Statement for Precise Transport NNovember 2020
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2. Motivation . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions used in this document . . . . . . . . . . . . . . 4
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Requirements Language . . . . . . . . . . . . . . . . . . 4
3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Problem with Traffic Scheduling Mechanisms . . . . . . . 4
3.2. Problem with Long-distance Transmission Delay and Jitter 5
3.3. Problem with SLA Guarantees of Dynamic Flows . . . . . . 5
3.4. Problem with Service Isolation . . . . . . . . . . . . . 6
3.5. Problem with Precise Resource Allocation . . . . . . . . 6
4. Security Considerations . . . . . . . . . . . . . . . . . . . 6
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. Normative References . . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
1.1. Overview
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
Xiong & Liu Expires May 5, 2021 [Page 2]
Internet-DraftThe Problem Statement for Precise Transport NNovember 2020
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
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.
1.2. Motivation
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. However, the
existing mechanisms are not sufficient for precise performance such
as precise latency, jitter variation, packet loss and more other
precise and deterministic properties.
Xiong & Liu Expires May 5, 2021 [Page 3]
Internet-DraftThe Problem Statement for Precise Transport NNovember 2020
As described in [xiong-rtgwg-precise-networking-requirements], 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 so as to the Precise Transport Networking. However, under
the existing IP network architecture with statistical multiplexing
characteristics, the existing deterministic technologies are facing
long-distance transmission, traffic scheduling, dynamic flows, per-
flow state maintenance and other controversial issues especially in
Wide Area Network (WAN) applications.
This document analyses the problems in existing deterministic
technologies to provide precise services in various industries such
as 5G networks.
2. Conventions used in this document
2.1. Terminology
The terminology is defined as [RFC8655] and [xiong-rtgwg-precise-
networking-requirements].
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. Problem Statement
3.1. Problem with Traffic Scheduling Mechanisms
As described in [RFC8655], the primary means by which DetNet achieves
its QoS assurances in IP networks is to eliminate the latency and
packet loss by the provision of sufficient resource at each node.
But only the resource itself is not sufficient, the traffic
scheduling mechanisms such as queuing, shaping, and scheduling
functions must be applied in L3 networks.
The congestion control, queue scheduling and other traffic mechanisms
which have been proposed in IEEE 802.1 TSN. But most of them are
based on the time synchronization and time cycle, such as
IEEE802.1Qbv, IEEE802.1Qch and so on. It will be difficult to
achieve precise time synchronization with all network nodes due to
deployment and cost reasons. And the shaping and queuing methods
Xiong & Liu Expires May 5, 2021 [Page 4]
Internet-DraftThe Problem Statement for Precise Transport NNovember 2020
which are not based on time synchronization such as IEEE802.1Qav and
IEEE802.1Qcr might not be suitable or available for some L3 networks
such as WAN application where multiple dynamic traffic flows may be
existed.
Moreover, the requirements of the all nodes in WAN networks to apply
the time synchronization and traffic scheduling mechanisms will also
lead to the difficulty of network scalability and deployment.
3.2. Problem with Long-distance Transmission Delay and Jitter
In WAN application, long-distance transmission will lead to
uncertainties, such as increasing transmission delay, jitter and
loss. The link delay of transmission is variable and can not be
ignored, and it must be considered in the end-to-end deterministic
forwarding mechanisms which are based on time synchronous. So the
following problems should be considered.
Precise measurement of the link delay.
The symmetry of bidirectional forwarding of the link delay.
Time cycle alignment in flows aggregation scenario.
3.3. Problem with SLA Guarantees of Dynamic 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
time window selection, queue processing and aggregation of multiple
flows.
Xiong & Liu Expires May 5, 2021 [Page 5]
Internet-DraftThe Problem Statement for Precise Transport NNovember 2020
Moreover, the existing solutions do not consider the characteristics
analysis of service requirements, including the impact of dynamic
characteristics analysis on the network, mainly about how to ensure
the certainty in the case of dynamic flows.
3.4. Problem with 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
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 and
hard isolated tunnel is required.
The resource reservation in DetNet can only ensure the statistical
reuse of bandwidth resources, but it can not guarantee the precise
isolation and control of instantaneous burst and can not realize the
hard isolation of each flow. The existing solutions cannot achieve
the requirements of service isolation.
3.5. Problem with Precise Resource Allocation
As described in [RFC8655], the primary means by which DetNet achieves
its QoS assurances is to reduce, or even completely eliminate, packet
loss by the provision of sufficient buffer storage at each node. But
it can not be achieved by not enough resource which can be allocated
due to practical and cost reason. The existing solutions can not
achieve the precise resource allocation.
4. Security Considerations
TBA
5. Acknowledgements
TBA
6. IANA Considerations
TBA
7. Normative References
[I-D.xiong-rtgwg-precise-tn-requirements]
Xiong, Q. and P. Liu, "The Requirements for Precise
Transport Networking", draft-xiong-rtgwg-precise-tn-
requirements-00 (work in progress), April 2020.
Xiong & Liu Expires May 5, 2021 [Page 6]
Internet-DraftThe Problem Statement for Precise Transport NNovember 2020
[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>.
[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>.
Authors' Addresses
Quan Xiong
ZTE Corporation
No.6 Huashi Park Rd
Wuhan, Hubei 430223
China
Email: xiong.quan@zte.com.cn
Peng Liu
China Mobile
Beijing 100053
China
Email: liupengyjy@chinamobile.com
Xiong & Liu Expires May 5, 2021 [Page 7]
