



PCE Working Group                                         R. Gandhi, Ed.
Internet-Draft                                       Cisco Systems, Inc.
Intended status: Standards Track                         29 January 2026
Expires: 2 August 2026


Extensions to the Path Computation Element Communication Protocol (PCEP)
               for Utilizing Bit Error Rate (BER) Metrics
                        draft-gandhi-pce-ber-01

Abstract

   IGP Traffic Engineering (TE) Metric Extensions describe mechanisms
   with which network performance information is distributed via OSPF
   IS-IS, and BGP-LS, respectively.  The Path Computation Element
   Communication Protocol (PCEP) provides mechanisms for Path
   Computation Elements (PCEs) to perform path computations in response
   to Path Computation Client (PCC) requests.  This document describes
   the extension to PCEP to utilize Bit Error Rate (BER) and Packet
   Error Rate (PER) as constraints for end-to-end path computation.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on 2 August 2026.

Copyright Notice

   Copyright (c) 2026 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
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   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components



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   extracted from this document must include Revised BSD License text as
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   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   3
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
     2.2.  Abbreviations . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  PCEP Extensions . . . . . . . . . . . . . . . . . . . . . . .   4
     4.1.  Extensions to METRIC Object . . . . . . . . . . . . . . .   5
     4.2.  Path BER Metric . . . . . . . . . . . . . . . . . . . . .   5
     4.3.  Path BER Metric Value . . . . . . . . . . . . . . . . . .   6
     4.4.  P2MP Path BER Metric  . . . . . . . . . . . . . . . . . .   6
     4.5.  Objective Functions . . . . . . . . . . . . . . . . . . .   7
       4.5.1.  TE Flex-Algorithm . . . . . . . . . . . . . . . . . .   7
   5.  Other Considerations  . . . . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  10
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   Networks may experience transmission bit errors due to various
   factors, such as poor fiber quality.  The bit error can be a single
   bit error or a burst of bit errors at a time.  Bit errors include
   layer-2 bit errors (e.g., causing CRC errors) or layer-3 and layer-4
   bit errors (e.g., causing checksum failures).  It is feasible to
   measure Bit Error Rate (BER) and Packet Error Rate (PER) of the links
   using measurement packets.  It is important that BER and PER metrics
   are also considered during the path selection process to be able to
   provide service level assurance.

   The Traffic Engineering Database (TED) is populated with network
   performance information like link latency, delay variation, packet
   loss, as well as parameters related to bandwidth (residual bandwidth,
   available bandwidth, and utilized bandwidth) via TE Metric Extensions
   in OSPF [RFC7471] or IS-IS [RFC8570] or via a management system.
   [RFC7823] describes how a Path Computation Element (PCE) [RFC5440]
   can use that information for path selection for explicitly routed
   LSPs.




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   A Path Computation Client (PCC) can request a PCE to provide a path
   meeting end-to-end network performance criteria.  This document
   extends the Path Computation Element Communication Protocol (PCEP)
   [RFC5440] to handle network performance constraints that also include
   BER and PER constraints.

2.  Conventions Used in This Document

2.1.  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.

2.2.  Abbreviations

   BER: Bit Error Rate

   EMA: Exponential Moving Average

   IGP: Interior Gateway Protocol

   IS-IS: Intermediate System to Intermediate System

   OF: Objective Function

   OSPF: Open Shortest Path First

   PCC: Path Computation Client

   PCE: Path Computation Element

   PER: Rate of Packets with Bit Errors

   RSVP: Resource Reservation Protocol

   TE: Traffic Engineering

   TED: Traffic Engineering Database










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3.  Overview

   [RFC8233] defines extensions to the PCEP to compute label switched
   paths.  This document further extends the path computation extensions
   defined in [RFC8233] to include Bit Error Rate (BER) and Packet Error
   Rate (PER) link metrics.  Note that the PCEP extensions defined in
   this document are equally applicable to the segment routing path
   computation defined in [RFC8664].

   Various BER metrics that can be used in path computation are:

   (1) Average BER

   (2) Maximum BER

   (3) Minimum BER

   (4) Exponential Moving Average of BER

   (5) Variance of BER (difference of minimum and average, for example)

   (6) BER anomaly state

   Various PER metrics that can be used in path computation are:

   (1) Average PER

   (2) Maximum PER

   (3) Minimum PER

   (4) Exponential Moving Average of PER

   (5) Variance of PER metrics (difference of minimum and average, for
   example)

   (6) PER anomaly state

4.  PCEP Extensions

   This section defines PCEP extensions (see [RFC5440]) to support bit
   error rate based network performance aware path computation.









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4.1.  Extensions to METRIC Object

   The METRIC object is defined in Section 7.8 of [RFC5440], comprising
   metric-value and metric-type (T field), and a flags field, comprising
   a number of bit flags (B bit and P bit).  This document defines the
   following types for the METRIC object.

   o TBA1: Path Average BER Metric

   o TBA2: Path Average PER Metric

   o TBA3: P2MP Path Average BER Metric

   o TBA4: P2MP Path Average PER Metric

   The following terminology is used and expanded along the way.

   o A network comprises of a set of N links {Li, (i=1...N)}.

   o A path P of a point-to-point (P2P) LSP is a list of K links
   {Lpi,(i=1...K)}.

4.2.  Path BER Metric

   [RFC7471] and [RFC8570] for IS-IS define "Unidirectional Link BER".
   The Path BER (as a percentage) metric type of the METRIC object in
   PCEP encodes a function of the unidirectional BER metrics of all
   links along a P2P path.  The end-to-end BER for the path is
   represented by this metric.  Specifically, extending on the above
   mentioned terminology:

   o The percentage link BER of link L is denoted PR(L).

   o The fractional link BER of link L is denoted FR(L) = PR(L)/100.

   o The percentage Path BER metric for the P2P path P = (1 -
   ((1-FR(Lp1)) * (1-FR(Lp2)) * .. * (1-FR(LpK)))) * 100 for a path P
   with links Lp1 to LpK.

   This is as per the composition function described in Section 5.1.5 of
   [RFC6049].

   Metric Type T = TBA1: Path BER metric

   Metric Type T = TBA2: Path PER metric






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   A PCC MAY use the Path BER metric in a PCReq message to request a
   path meeting the end-to-end BER requirement.  In this case, the B bit
   MUST be set to suggest a bound (a maximum) for the Path BER metric
   that must not be exceeded for the PCC to consider the computed path
   as acceptable.  The Path BER metric must be less than or equal to the
   value specified in the metric-value field.

   A PCC can also use this metric to ask the PCE to optimize the path
   BER during path computation.  In this case, the B flag MUST be
   cleared.

   A PCE MAY use the Path BER metric in a PCRep message along with a NO-
   PATH object in the case where the PCE cannot compute a path meeting
   this constraint.  A PCE can also use this metric to send the computed
   end-to-end BER metric to the PCC.

4.3.  Path BER Metric Value

   The TE metrics specified in [RFC7471] for OSPF, [RFC8570] for IS-IS,
   and [RFC8571] for BGP are further extended to distribute
   "Unidirectional Link BER Sub-TLV" to advertise the link BER in
   percentage in a 24-bit field.  [RFC5440] defines the METRIC object
   with a 32-bit metric value encoded in IEEE floating point format (see
   (IEEE.754)).  Consequently, the encoding for the Path BER metric
   value is quantified as a percentage and encoded in IEEE floating
   point format.

4.4.  P2MP Path BER Metric

   This section defines the following types for the METRIC object to be
   used for the P2MP TE LSPs.

   The P2MP Path BER metric type of the METRIC object in PCEP encodes
   the path BER metric for the destination that observes the worst BER
   metric among all destinations of the P2MP tree.  Specifically,
   extending on the above-mentioned terminology:

   o A P2MP tree T comprises of a set of M destinations {Dest_j,
   (j=1...M)}.

   o The P2P Path BER metric of the path to destination Dest_j is
   denoted by PRM(Dest_j).

   o The P2MP Path BER metric for the P2MP tree T = Maximum
   {PRM(Dest_j), (j=1...M)}.

   Metric Type T = TBA3: P2MP Path BER metric




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   Metric Type T = TBA4: P2MP Path PER metric

4.5.  Objective Functions

   [RFC5541] defines a mechanism to specify an objective function that
   is used by a PCE when it computes a path.  For path BER, the
   following new OF is defined.

   o A network comprises a set of N links {Li, (i=1...N)}.

   o A path P is a list of K links {Lpi,(i=1...K)}.

   o The percentage link BER of link L is denoted PR(L).

   o The fractional link BER of link L is denoted FR(L) = PR(L) / 100.

   o The percentage path BER of a path P is denoted PR(P), where PR(P) =
   (1 - ((1-FR(Lp1)) * (1-FR(Lp2)) * .. * (1-FR(LpK)))) * 100.

   Objective Function Code: TBA6 Name: Minimum BER Path (MBERP)
   Description: Find a path P such that PR(P) is minimized.

   If the objective functions defined in this document are unknown/
   unsupported by a PCE, then the procedure as defined in Section 3.1.1
   of [RFC5541] is followed.

4.5.1.  TE Flex-Algorithm

   New Flexible algorithm type is defined for TE that uses BER and PER
   metrics.

   Editor's note: Additional details will be added in the future version
   of this document.

5.  Other Considerations

   The new metric type and objective functions defined in this document
   can also be used with the stateful PCE extensions defined in RFC 8231
   for PCI-initiated LSPs.  The format of PCEP messages described in
   [RFC8231] uses (intended-attribute-list) and (attribute-list),
   respectively, (where the (intended-attribute-list) is the attribute-
   list defined in Section 6.5 of [RFC5440] and extended in this
   document) for BER parameters.








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   A stateful PCE can also determine which LSPs should be reoptimized
   based on network events or triggers from external monitoring systems.
   For example, when a particular link deteriorates and its BER
   increases, this can trigger the stateful PCE to automatically
   determine which LSPs are impacted and should be reoptimized.

6.  Security Considerations

   The security considerations specified in [RFC5440], [RFC8231],
   [RFC8233], and [RFC8664] apply to the procedure and extensions
   defined in this document.

7.  IANA Considerations

   IANA maintains the "Path Computation Element Protocol (PCEP) Numbers"
   registry.  Within this registry, IANA maintains a subregistry for
   "METRIC Object T Field".  New metric types are defined in this
   document for the METRIC object (specified in [RFC5440]).  IANA is
   requested to allocate the values for these METRIC types.

         +=======+==============================+===============+
         | Value |         Description          | Reference     |
         +=======+==============================+===============+
         | TBA1  |   Path Average BER Metric    | This document |
         +-------+------------------------------+---------------+
         | TBA2  |   Path Average PER Metric    | This document |
         +-------+------------------------------+---------------+
         | TBA3  | P2MP Path Average BER Metric | This document |
         +-------+------------------------------+---------------+
         | TBA4  | P2MP Path Average PER Metric | This document |
         +-------+------------------------------+---------------+

                          Table 1: Metric Types:

   Editor's note: Additional types for carrying minimum, maximum, and
   variance of the BER and PER metrics will be defined in the future
   revision of this document.

8.  References

8.1.  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>.





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   [RFC5440]  Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              DOI 10.17487/RFC5440, March 2009,
              <https://www.rfc-editor.org/info/rfc5440>.

   [RFC8231]  Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path
              Computation Element Communication Protocol (PCEP)
              Extensions for Stateful PCE", RFC 8231,
              DOI 10.17487/RFC8231, September 2017,
              <https://www.rfc-editor.org/info/rfc8231>.

   [RFC8233]  Dhody, D., Wu, Q., Manral, V., Ali, Z., and K. Kumaki,
              "Extensions to the Path Computation Element Communication
              Protocol (PCEP) to Compute Service-Aware Label Switched
              Paths (LSPs)", RFC 8233, DOI 10.17487/RFC8233, September
              2017, <https://www.rfc-editor.org/info/rfc8233>.

   [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>.

   [RFC5541]  Le Roux, JL., Vasseur, JP., and Y. Lee, "Encoding of
              Objective Functions in the Path Computation Element
              Communication Protocol (PCEP)", RFC 5541,
              DOI 10.17487/RFC5541, June 2009,
              <https://www.rfc-editor.org/info/rfc5541>.

8.2.  Informative References

   [RFC6049]  Morton, A. and E. Stephan, "Spatial Composition of
              Metrics", RFC 6049, DOI 10.17487/RFC6049, January 2011,
              <https://www.rfc-editor.org/info/rfc6049>.

   [RFC7471]  Giacalone, S., Ward, D., Drake, J., Atlas, A., and S.
              Previdi, "OSPF Traffic Engineering (TE) Metric
              Extensions", RFC 7471, DOI 10.17487/RFC7471, March 2015,
              <https://www.rfc-editor.org/info/rfc7471>.

   [RFC7823]  Atlas, A., Drake, J., Giacalone, S., and S. Previdi,
              "Performance-Based Path Selection for Explicitly Routed
              Label Switched Paths (LSPs) Using TE Metric Extensions",
              RFC 7823, DOI 10.17487/RFC7823, May 2016,
              <https://www.rfc-editor.org/info/rfc7823>.

   [RFC8570]  Ginsberg, L., Ed., Previdi, S., Ed., Giacalone, S., Ward,
              D., Drake, J., and Q. Wu, "IS-IS Traffic Engineering (TE)
              Metric Extensions", RFC 8570, DOI 10.17487/RFC8570, March
              2019, <https://www.rfc-editor.org/info/rfc8570>.



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   [RFC8571]  Ginsberg, L., Ed., Previdi, S., Wu, Q., Tantsura, J., and
              C. Filsfils, "BGP - Link State (BGP-LS) Advertisement of
              IGP Traffic Engineering Performance Metric Extensions",
              RFC 8571, DOI 10.17487/RFC8571, March 2019,
              <https://www.rfc-editor.org/info/rfc8571>.

   [RFC8664]  Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
              and J. Hardwick, "Path Computation Element Communication
              Protocol (PCEP) Extensions for Segment Routing", RFC 8664,
              DOI 10.17487/RFC8664, December 2019,
              <https://www.rfc-editor.org/info/rfc8664>.

Acknowledgments

   Thank you.

Author's Address

   Rakesh Gandhi (editor)
   Cisco Systems, Inc.
   Canada
   Email: rgandhi@cisco.com





























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