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 Gandhi Expires 24 January 2027 [Page 1] Internet-Draft PCEP Extensions for Link BER July 2026 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. Gandhi Expires 24 January 2027 [Page 2] Internet-Draft PCEP Extensions for Link BER July 2026 [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 Gandhi Expires 24 January 2027 [Page 3] Internet-Draft PCEP Extensions for Link BER July 2026 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]. Gandhi Expires 24 January 2027 [Page 4] Internet-Draft PCEP Extensions for Link BER July 2026 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. Gandhi Expires 24 January 2027 [Page 5] Internet-Draft PCEP Extensions for Link BER July 2026 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. Gandhi Expires 24 January 2027 [Page 6] Internet-Draft PCEP Extensions for Link BER July 2026 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. Gandhi Expires 24 January 2027 [Page 7] Internet-Draft PCEP Extensions for Link BER July 2026 +=======+==========================+===============+ | 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, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC 5440, DOI 10.17487/RFC5440, March 2009, . [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, . [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, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . Gandhi Expires 24 January 2027 [Page 8] Internet-Draft PCEP Extensions for Link BER July 2026 [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, . [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, . [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, . 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, . [RFC6049] Morton, A. and E. Stephan, "Spatial Composition of Metrics", RFC 6049, DOI 10.17487/RFC6049, January 2011, . [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, . [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, . [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, . Gandhi Expires 24 January 2027 [Page 9] Internet-Draft PCEP Extensions for Link BER July 2026 [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, . Acknowledgments TBA. Author's Address Rakesh Gandhi (editor) Cisco Systems, Inc. Canada Email: rgandhi@cisco.com Gandhi Expires 24 January 2027 [Page 10]