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Network Working Group                                            L. Geng
Internet-Draft                                                   L. Wang
Intended status: Informational                              China Mobile
Expires: January 3, 2019                                        L. Qiang
                                                     Huawei Technologies
                                                            July 2, 2018


    Technical Requirements of Bounded Latency in Large-scale DetNet
                               Deployment
           draft-geng-detnet-requirements-bounded-latency-00

Abstract

   This document summarizes the technical requirements of bounded
   latency of DetNet system in large-scale deployment.

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
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   This Internet-Draft will expire on January 3, 2019.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
     1.2.  Terminology & Abbreviations . . . . . . . . . . . . . . .   3
   2.  End-to-end bounded latency requirements . . . . . . . . . . .   3
   3.  Tolerance of time deviation . . . . . . . . . . . . . . . . .   4
   4.  Massive number of deterministic flows . . . . . . . . . . . .   4
   5.  Stable jitter with long transmission delay  . . . . . . . . .   4
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   Deterministic Networking (DetNet) enables the transmission of
   specific data flows in large scale networks with extremely low data
   loss rates and bounded latency. [draft-ietf-detnet-problem-statement]
   outlines the problems that need to be resolved in DetNet, and
   [draft-ietf-detnet-use-cases] presents the use cases in which DetNet
   deployment is found beneficial and useful.

   In DetNet WG, many of the technical requirements and solution have
   been discussed In order to achieve deterministic networking
   performance in large-scale network.  This mainly include the
   following aspect.

   o  DetNet Definition and architecture are discussed in
      [draft-ietf-detnet-architecture]

   o  Encapsulation methods are discussed in[draft-ietf-detnet-dp-sol]
      with specific mechanisms for identification of DetNet services and
      approaches for reliable transmission (i.e.  Replication of
      packets).

   o  Security requirements are specially discussed in
      [draft-ietf-detnet-security].

   To some extend, TSN is assumed to be used for Layer 2 underlay for
   DetNet services to guarantee the bounded latency performance.
   However, TSN is originally designed for LAN scenario which suffers
   from scalability problems (i.e. end-to-end time synchronization,
   sensitive jitter performance subject to transmission latency).
   Meanwhile, it is also considered challenging to using MPLS/IP
   encapsulation for DetNet service in which the forwarding plane is
   purely based on Layer 2 TSN technology.  There is yet a document



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   which specifically discusses the requirements of bounded latency with
   an assumption that DetNet runs as an standalone underlay technology
   rather than an overlay of TSN.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119.

1.2.  Terminology & Abbreviations

   This document uses the terminology defined in
   [draft-ietf-detnet-architecture].

   TSN: Time Sensitive Network

2.  End-to-end bounded latency requirements

   As [draft-ietf-detnet-dp-sol] declares, there are two types of
   scenarios considered in DetNet as shown in Figure 1: (i) inter-
   connect TSN domains scenario, and (ii) native connectivity between
   DetNet-aware end systems.

       +--------------+                             +--------------+
       |              |                             |              |
       | TSN Domain I +-----------------------------+ TSN Domain II|
       |              |                             |              |
       +--------------+                             +--------------+

                       (i) Inter-connect TSN Domains

       +--------------+                           +--------------+
       |DetNet Device +---------------------------+DetNet Device |
       +--------------+                           +--------------+

         (ii) Native Connectivity between DetNet-aware End Systems

                  Figure 1: Two Types of DetNet Scenarios

   Req 1: Stitching TSN domains with bounded latency.

   In scenario (i) TSN islands are bridged through DetNet connections,
   and time synchronization is required inside each TSN domain.  Note
   that different TSN domains may be misaligned in time and it may not
   be feasible to achieve end-to-end time synchronization in large
   scale.  It is the DetNet domain who has to maintain the bounded
   latency performance between the separated TSN domains.



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   Req 2: Flexible and fast convergence mechanism as new DetNet flow is
   created.

   Considering the features of TSN applications we can speculate that
   the applications in scenario (i) are usually in a simple manner,
   which means the number of deterministic flows will not dramatically
   change with time.  At the same time, the traffic patterns are
   relative regular.  While in scenario (ii) there are more bandwidth-
   greddy applications such as VR communication.  They may require
   establishment or tear-down of the DetNet connections frequently.
   Mechanisms like IEEE 802.1 Qch, and IEEE 802.1 Qbv which need re-
   computation whenever new flow are added may be not suitable for this
   case.  In order to deploy DetNet services in scenario (ii).

3.  Tolerance of time deviation

   Req 3: Tolerance of a certain level of end-to-end time deviation.

   Different from the TSN services which are deployed in small-scale
   local area network, DetNet service targets at large scale
   implementation.  There are a great amount of heterogeneous devices in
   large scale network.  It will be difficult and costly to keep precise
   synchronization among all devices.  It is worthy of have a DetNet
   system which can keep the bounded latency performance even under an
   unsynchronized situation..

4.  Massive number of deterministic flows

   Req 4: Fine-grained and scalable resource reservation method.

   Resource reservation for individual DetNet flows are required in
   order to maintain per-flow state in the devices along the path.
   Given a large number of DetNet flows, aggregation of such resource
   reservation may be necessary at least at the core routers.  However,
   aggregating massive DetNet flows into a tunnel will sacrifice some
   network resources or accuracy, just like change from DiffServ to
   IntServ.  Certain trade-off needs to be studied carefully to achieve
   optimal performance.

5.  Stable jitter with long transmission delay

   Req 5: Tolerance of transmission latency

   Large transmission latency is expected in large scale network which
   may further lead to larger jitter in some mechanisms such as IEEE
   802.1 Qch. It would be preferred to have a mechanism where the jitter
   performance does not scale up with the transmission latency.  Thus




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   end user can have same bounded latency performance in a P2MP
   deployment.

6.  IANA Considerations

   This document makes no request of IANA.

7.  Security Considerations

   This document will not introduce new security problems.

8.  Acknowledgements

   TBD.

9.  Normative References

   [draft-ietf-detnet-architecture]
              "DetNet Architecture", <https://datatracker.ietf.org/doc/
              draft-ietf-detnet-architecture/>.

   [draft-ietf-detnet-dp-sol]
              "DetNet Data Plane Encapsulation",
              <https://datatracker.ietf.org/doc/
              draft-ietf-detnet-dp-sol/>.

   [draft-ietf-detnet-problem-statement]
              "DetNet Problem Statement",
              <https://datatracker.ietf.org/doc/
              draft-ietf-detnet-problem-statement/>.

   [draft-ietf-detnet-security]
              "DetNet Security Considerations",
              <https://datatracker.ietf.org/doc/
              draft-ietf-detnet-security/>.

   [draft-ietf-detnet-use-cases]
              "DetNet Use Cases", <https://datatracker.ietf.org/doc/
              draft-ietf-detnet-use-cases/>.

   [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>.







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Authors' Addresses

   Liang Geng
   China Mobile
   Beijing
   China

   Email: gengliang@chinamobile.com


   Lei Wang
   China Mobile
   Beijing
   China

   Email: wangleiyjy@chinamobile.com


   Li Qiang
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing  100095
   China

   Email: qiangli3@huawei.com


























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