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Versions: 00 01                                                         
MPLS Working Group                                               F. Yang
Internet-Draft                                       Huawei Technologies
Intended status: Informational                                    L. Han
Expires: May 6, 2021                                        China Mobile
                                                                 J. Zhao
                  China Academy of Information Communications Technology
                                                        November 2, 2020


    Problem Statement of Signal Degrade Indication for SR over MPLS
                      draft-yang-mpls-ps-sdi-sr-01

Abstract

   This document outlines the problem statements and the use cases
   needed to be taken into account when the signal degrade is detected
   and indicated in Segment Routing (SR) over MPLS networks.

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 [RFC2119].

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 6, 2021.

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



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   (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
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Problem Statement and Use Case  . . . . . . . . . . . . . . .   3
     3.1.  Overview of Signal Degrade in SR over MPLS Network  . . .   3
     3.2.  Influence on Voice and Data Service . . . . . . . . . . .   4
     3.3.  Engineering Considerations  . . . . . . . . . . . . . . .   4
       3.3.1.  Signal Degrade in Diversity of PHYs . . . . . . . . .   4
       3.3.2.  Performance Management Detection  . . . . . . . . . .   4
       3.3.3.  BFD Detection . . . . . . . . . . . . . . . . . . . .   5
     3.4.  LER and LSR Consideration . . . . . . . . . . . . . . . .   5
     3.5.  Signal Degrade Approach . . . . . . . . . . . . . . . . .   5
     3.6.  Parameter Threshold . . . . . . . . . . . . . . . . . . .   5
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   Signal Failure (SF) and Signal Degrade (SD) are categorized as the
   trigger to bring the survivability challenge to the network in
   [RFC4428].  Signal Failure (SF) can be interpreted as the absence of
   the network resources, and Signal Degrade (SD) can be regarded as the
   decrease of the signal quality quantifiable measurement.  The
   meanings of signal failure is straightforward, indicating the failure
   of the interfaces, links or nodes.  Meanwhile, fiber aging, fiber
   impairment, fiber pollution, optical module mismatch or WDM
   transmission error are the potential reasons to generate signal
   degrade.

   Segment Routing(SR) leverages the source routing paradigm.  In the
   era of source routing paradigm, Segment Routing over MPLS (SR-MPLS)
   [RFC8402] has been widely utilized for different kinds of network
   scenarios.  It is valuable to investigate the necessity of supporting
   detection of Signal Degrade (SD) in the source routing paradigm.



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   This document gives the problem statements for the Signal Degrade
   indication and advertisement in the networks of SR over MPLS (SR-
   MPLS).  The triggered protection mechanism is irrelevant to Signal
   Degrade indication and consequently is out of scope.

2.  Terminology

   SD: Signal Degrade

   PLR: Packet Loss Rate

   SLA: Service Level Agreement

   FEC: Forwarding Error Correction

   BFD: Bidirectional Forwarding Detection

3.  Problem Statement and Use Case

3.1.  Overview of Signal Degrade in SR over MPLS Network

                  +-----+     +-----+
          +-------|LSR1 |-----|LSR2 |------+
          |       +-----+     +-----+      |
          |             \    /             |
          |              \  /              |
        +-----+         +-----+         +-----+
   -----|LER1 |         |LSR5 |         |LER2 |-----
        +-----+         +-----+         +-----+
          |              /  \              |
          |             /    \             |
          |       +-----+     +-----+      |
          +-------|LSR3 |-----|LSR4 |------+
                  +-----+     +-----+

       Figure 1: Overview of Signal Degrade in SR over MPLS Network

   Figure 1 depicts the overview of the signal degrade detection in the
   segment routing over MPLS network.  LER1 and LER2 are the Label Edge
   Routers, and LSR1 to LSR5 are the Label Switching Routers.  The
   signal degrade can happen at any links in the SR over MPLS network,
   not only the links connected to LERs, but also the links between
   LSRs.  There is no signal degrade is defined in the current OAM
   [I-D.ietf-spring-sr-oam-requirement] or BFD
   [I-D.ali-spring-bfd-sr-policy] mechanisms designed for SR over MPLS
   network.





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3.2.  Influence on Voice and Data Service

   In mobile backhaul network, signal degrade may not lead to service
   interruption, however it impairs the services and dissatisfies the
   Service Level Agreements (SLAs).  Take VoLTE service as an example,
   signal degrade over the optical transmission can bring noise, carton,
   call delay, drop line or even cause base station disconnection.  In
   addition, the download speed of data service would decrease
   dramatically when signal degrade increases.  There are some
   statistics captured from live network shown in Table 1.

             +------------------+---------------------------+
             | Packet Loss Rate | Decrease of Download Rate |
             +------------------+---------------------------+
             | 0                | No affect                 |
             | <0.01%           | No affect                 |
             | 0.05%            | 23%                       |
             | 0.2%             | 58%                       |
             | 1%               | 75%                       |
             +------------------+---------------------------+

    Table 1 Relation between Packet Loss Rate and Decrease of Download
                                   Rate

3.3.  Engineering Considerations

3.3.1.  Signal Degrade in Diversity of PHYs

   From the perspective of engineering, there are a variety of PHYs
   defined in IEEE 802.3.  The PHYs without Forward Error Correction
   (FEC) generates the defects/alarms, PHYs with the FEC correct the bit
   errors.  There is no uniform mechanism to guarantee the control of
   the bit errors.

3.3.2.  Performance Management Detection

   The approaches of OAM performance management can be used as the tools
   to detect the signal degrade.  On one hand, active performance
   management cannot fulfill the Signal Degrade detection all the time.
   On the other hand, passive performance management consumes too much
   resource of the equipment so that operators can hardly use it in the
   networks.  The current performance management mechanism is not
   feasible to detect signal degrade conveniently and efficiently.








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3.3.3.  BFD Detection

   For the worst case, when signal degrade happens on LSRs, the current
   best practice is to make use of the result of BFD protocol on LERs to
   trigger the protection mechanism.  The detection time is at least
   3.3ms*3 later than the time when the signal degrade happens.  If the
   LSRs can trigger the protection protocol in a more direct and
   efficient way, the network service interruption time can be reduced.

3.4.  LER and LSR Consideration

   There are local and remote request logics about the signal degrade
   defined in [RFC6378].  Meanwhile, the Protection State Coordination
   (PSC) process and the messages are utilized to advertise and exchange
   the signal degrade state between LERs.  In the network of MPLS-TP,
   the LSRs stay dumb in the transmission of OAM messages.

   In the SR over MPLS networks, only the headend LER knows all the
   segments in the label stack, the other LSRs and LER2 does not know
   the entire label stack.  As for the signal degrade happens on either
   headend LER or other LSRs and LER, the mechanism of the signal
   degrade indication would be differently designed.

3.5.  Signal Degrade Approach

   In Section 4.1 of [RFC6372], approaches of detection or recognition
   of network defect such as signal degrade are specified.  The signal
   degrade indication can be detected from a network defect, or
   advertised by an in-band data-plane-based OAM mechanism, or by in-
   band or out-of-band control-plane signaling, or triggered from the
   centralized Network Management System (NMS) or a SDN controller.  The
   appropriate approaches should be wisely selected.

3.6.  Parameter Threshold

   Parameters like BER or PLR are the different quantitative measurement
   methods.  It is flexible for the service providers to set different
   values of threshold based on the geographical site investigations.
   For an even more complicated scenario, the threshold may be defined
   differently in terms of services, for example to differentiate the
   requirements of the eMBB or URLLC applications in 5G era.

4.  IANA Considerations

   This document makes no request of IANA.

   Note to RFC Editor: this section may be removed on publication as an
   RFC.



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5.  Security Considerations

   This document has no consideration of security.

   Note to RFC Editor: this section may be removed on publication as an
   RFC.

6.  Acknowledgements

   TBD

7.  References

7.1.  Normative References

   [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>.

7.2.  Informative References

   [I-D.ali-spring-bfd-sr-policy]
              Ali, Z., Talaulikar, K., Filsfils, C., Nainar, N., and C.
              Pignataro, "Bidirectional Forwarding Detection (BFD) for
              Segment Routing Policies for Traffic Engineering", draft-
              ali-spring-bfd-sr-policy-05 (work in progress), May 2020.

   [I-D.ietf-spring-sr-oam-requirement]
              Kumar, N., Pignataro, C., Akiya, N., Geib, R., Mirsky, G.,
              and S. Litkowski, "OAM Requirements for Segment Routing
              Network", draft-ietf-spring-sr-oam-requirement-03 (work in
              progress), January 2017.

   [RFC4428]  Papadimitriou, D., Ed. and E. Mannie, Ed., "Analysis of
              Generalized Multi-Protocol Label Switching (GMPLS)-based
              Recovery Mechanisms (including Protection and
              Restoration)", RFC 4428, DOI 10.17487/RFC4428, March 2006,
              <https://www.rfc-editor.org/info/rfc4428>.

   [RFC6372]  Sprecher, N., Ed. and A. Farrel, Ed., "MPLS Transport
              Profile (MPLS-TP) Survivability Framework", RFC 6372,
              DOI 10.17487/RFC6372, September 2011,
              <https://www.rfc-editor.org/info/rfc6372>.







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   [RFC6378]  Weingarten, Y., Ed., Bryant, S., Osborne, E., Sprecher,
              N., and A. Fulignoli, Ed., "MPLS Transport Profile (MPLS-
              TP) Linear Protection", RFC 6378, DOI 10.17487/RFC6378,
              October 2011, <https://www.rfc-editor.org/info/rfc6378>.

   [RFC7271]  Ryoo, J., Ed., Gray, E., Ed., van Helvoort, H.,
              D'Alessandro, A., Cheung, T., and E. Osborne, "MPLS
              Transport Profile (MPLS-TP) Linear Protection to Match the
              Operational Expectations of Synchronous Digital Hierarchy,
              Optical Transport Network, and Ethernet Transport Network
              Operators", RFC 7271, DOI 10.17487/RFC7271, June 2014,
              <https://www.rfc-editor.org/info/rfc7271>.

   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
              July 2018, <https://www.rfc-editor.org/info/rfc8402>.

Authors' Addresses

   Fan Yang
   Huawei Technologies

   Email: shirley.yangfan@huawei.com


   Liuyan Han
   China Mobile

   Email: hanliuyan@chinamobile.com


   Junfeng Zhao
   China Academy of Information Communications Technology

   Email: zhaojunfeng@caict.ac.cn















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