Extensions to the Path Computation Element Communication Protocol (PCEP) for Utilizing Link Bit Error Rate (BER) Metric
draft-gandhi-pce-ber-02
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Author | Rakesh Gandhi | ||
| Last updated | 2026-07-23 | ||
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draft-gandhi-pce-ber-02
PCE Working Group R. Gandhi, Ed.
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track 23 July 2026
Expires: 24 January 2027
Extensions to the Path Computation Element Communication Protocol (PCEP)
for Utilizing Link Bit Error Rate (BER) Metric
draft-gandhi-pce-ber-02
Abstract
Networks may experience transmission bit errors due to various
factors, such as poor fiber quality. 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 extensions to PCEP to include link Bit Error Rate (BER) metric as
a constraint for end-to-end path computation. The PCEP extension
utilize link BER metric advertisements defined for IS-IS and OSPF in
draft-gandhi-lsr-ber.
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 24 January 2027.
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
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
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and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
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. METRIC Object Types . . . . . . . . . . . . . . . . . . . 4
4.2. Path BER Metric . . . . . . . . . . . . . . . . . . . . . 4
4.2.1. Objective Function . . . . . . . . . . . . . . . . . 5
4.3. P2MP Path BER Metric . . . . . . . . . . . . . . . . . . 6
4.3.1. P2MP Objective Function . . . . . . . . . . . . . . . 6
4.4. TE Flex-Algorithm . . . . . . . . . . . . . . . . . . . . 6
5. Other Considerations . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7.1. Metric Types . . . . . . . . . . . . . . . . . . . . . . 7
7.2. Objective Function Code . . . . . . . . . . . . . . . . . 7
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 Cyclic Redundancy Check (CRC)
errors) or layer-3 and layer-4 bit errors (e.g., causing checksum
failures). It is important that link BER metric is considered during
the path selection process 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.
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[RFC7823] describes how a Path Computation Element (PCE) [RFC5440]
can use that information for path selection for explicitly routed
Label Switched Paths (LSPs). A Path Computation Client (PCC) can
request a PCE to provide a path meeting end-to-end network
performance criteria. [RFC8233] defines extensions to PCEP to
compute service-aware Label Switched Paths (LSPs).
This document extends the Path Computation Element Communication
Protocol (PCEP) to include link Bit Error Rate (BER) metric as a
constraint for end-to-end path computation. The PCEP extensions
utilize link BER metric advertisements defined for IS-IS and OSPF in
[I-D.gandhi-lsr-ber].
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
TE: Traffic Engineering
TED: Traffic Engineering Database
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3. Overview
This document further extends the service-aware path computation
extensions for LSPs defined in [RFC8233] to include link Bit Error
Rate (BER) metric as a constraint for end-to-end path computation.
Note that the PCEP extensions defined in this document are equally
applicable to Segment Routing path computation defined in [RFC8664].
The procedure for multipath Segment Routing will be added in a future
revision.
The PCEP extensions for including link PER metric will be added in a
future revision.
4. PCEP Extensions
This section defines PCEP extensions (see [RFC5440]) to support link-
BER-based path computation.
4.1. METRIC Object Types
The METRIC object is defined in Section 7.8 of [RFC5440]. It
comprises metric-value and metric-type (T field), and a flags field
containing a number of bit flags (B bit and C bit).
This document specifies additional types for the METRIC object to
enable encoding of BER metric types. The following metric types (T
field) for the METRIC object ae defined.
o Metric Type T=TBA1: Path BER Metric
o Metric Type T=TBA2: P2MP Path BER Metric
The following terminology is used and expanded along the way.
o A network comprises 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
The Path BER metric (as a percentage) as a metric-value in the METRIC
object in PCEP encodes a function of the unidirectional BER metric of
all links along a P2P path.
This follows the composition function described in Section 5.1.5 of
[RFC6049].
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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.
A PCC MAY use the Path BER metric type in a PCReq message to request
a path that meets the end-to-end BER metric 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 the Path BER metric type to ask the PCE to
optimize the path BER metric during path computation. In this case,
the C bit MUST be set and the B bit MUST be cleared.
A PCE MAY use the Path BER metric type in a PCRep message along with
a NO-PATH object in the case where the PCE cannot compute a path
meeting this constraint.
[RFC5440] defines the METRIC object with a 32-bit metric value
encoded in IEEE floating point format (see (IEEE.754)).
The encoding for the Path BER metric value is quantified in units of
percentage and encoded in IEEE floating point format.
For use in the PCEP METRIC object, the 24-bit unsigned integer BER
value as defined [I-D.gandhi-lsr-ber] is converted to a 32-bit IEEE
floating point value. This conversion follows the procedure
specified in [IEEE.754.2019].
4.2.1. Objective Function
[RFC5541] defines a mechanism to specify an objective function (OF)
that is used by a PCE when it computes a path. For Path BER Metric,
the following new OF is defined when using the Path BER metric
(TBA1).
Objective Function Code: TBA3
Name: Minimum BER Path (MBERP)
Description: Find a path P such that PR(P) is minimized.
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If the objective function defined in this document is unknown/
unsupported by a PCE, then the procedure as defined in Section 3.1.1
of [RFC5541] is followed.
4.3. P2MP Path BER Metric
The P2MP Path BER metric in a metric-value of the METRIC object in
PCEP encodes the Path BER Metric for the destination that observes
the worst path BER metric among all destinations of the P2MP tree.
Specifically, extending on the above-mentioned terminology:
o A P2MP tree T comprises 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)}.
4.3.1. P2MP Objective Function
For P2MP path computation using the P2MP Path BER metric (TBA2), the
objective-function procedures defined in [RFC8306] apply. In
particular, this document reuses the P2MP objective functions defined
in [RFC8306] and does not define a new P2MP-specific objective
function code for BER.
4.4. TE Flex-Algorithm
Flexible Algorithm (Flex-Algo) in Path Computation Element
Communication Protocol (PCEP) enables Path Computation Elements
(PCEs) to compute constrained paths using user-defined IGP algorithm
metrics.
[RFC9933] defines PCEP extensions for carrying SR-Algorithm for TE.
A new Flexible Algorithm Definition (FAD) type is defined for PCEP
based on link BER metric for path computation using the IGP Flex-Algo
definition specified in [I-D.gandhi-lsr-flex-algo-link-ber].
Additional details will be added in a future revision of this
document.
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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
[RFC8231] for PCE-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 link BER parameters.
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 metric
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.
7.1. Metric Types
+=======+======================+===============+
| Value | Description | Reference |
+=======+======================+===============+
| TBA1 | Path BER Metric | This document |
+-------+----------------------+---------------+
| TBA2 | P2MP Path BER Metric | This document |
+-------+----------------------+---------------+
Table 1: Metric Types
7.2. Objective Function Code
IANA also maintains a subregistry for "PCEP Objective Function (OF)
Codes". This document defines a new objective function code
(specified in [RFC5541]). IANA is requested to allocate the value
for this OF code.
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+=======+==========================+===============+
| Value | Description | Reference |
+=======+==========================+===============+
| TBA3 | Minimum BER Path (MBERP) | This document |
+-------+--------------------------+---------------+
Table 2: Objective Function Code
8. References
8.1. Normative References
[I-D.gandhi-lsr-ber]
Gandhi, R., "IS-IS, OSPF, and BGP-LS Extensions for
Advertising Bit Error Rate Metric for Traffic
Engineering", Work in Progress, Internet-Draft, draft-
gandhi-lsr-ber-02, 18 July 2026,
<https://datatracker.ietf.org/doc/html/draft-gandhi-lsr-
ber-02>.
[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>.
[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>.
[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>.
[RFC8306] Zhao, Q., Dhody, D., Ed., Palleti, R., and D. King,
"Extensions to the Path Computation Element Communication
Protocol (PCEP) for Point-to-Multipoint Traffic
Engineering Label Switched Paths", RFC 8306,
DOI 10.17487/RFC8306, November 2017,
<https://www.rfc-editor.org/info/rfc8306>.
[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>.
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[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>.
[RFC9933] Sidor, S., Rose, Z., Peng, S., Peng, S., and A. Stone,
"Carrying SR-Algorithm in Path Computation Element
Communication Protocol (PCEP)", RFC 9933,
DOI 10.17487/RFC9933, July 2026,
<https://www.rfc-editor.org/info/rfc9933>.
8.2. Informative References
[I-D.gandhi-lsr-flex-algo-link-ber]
Gandhi, R., "IGP Flexible Algorithm Utilizing Link Bit
Error Rate Metric", Work in Progress, Internet-Draft,
draft-gandhi-lsr-flex-algo-link-ber-00, 18 July 2026,
<https://datatracker.ietf.org/doc/html/draft-gandhi-lsr-
flex-algo-link-ber-00>.
[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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[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
TBA.
Author's Address
Rakesh Gandhi (editor)
Cisco Systems, Inc.
Canada
Email: rgandhi@cisco.com
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