PCE Working Group R. Gandhi, Ed. Internet-Draft Cisco Systems, Inc. Intended status: Standards Track 22 July 2025 Expires: 23 January 2026 Extensions to the Path Computation Element Communication Protocol (PCEP) for Utilizing Bit Error Rate (BER) Metrics draft-gandhi-pce-ber-00 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 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 23 January 2026. Copyright Notice Copyright (c) 2025 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 and restrictions with respect to this document. Code Components Gandhi Expires 23 January 2026 [Page 1] Internet-Draft PCEP Extensions for BER July 2025 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. 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. Gandhi Expires 23 January 2026 [Page 2] Internet-Draft PCEP Extensions for BER July 2025 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 Gandhi Expires 23 January 2026 [Page 3] Internet-Draft PCEP Extensions for BER July 2025 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. Gandhi Expires 23 January 2026 [Page 4] Internet-Draft PCEP Extensions for BER July 2025 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 Gandhi Expires 23 January 2026 [Page 5] Internet-Draft PCEP Extensions for BER July 2025 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 Gandhi Expires 23 January 2026 [Page 6] Internet-Draft PCEP Extensions for BER July 2025 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. Gandhi Expires 23 January 2026 [Page 7] Internet-Draft PCEP Extensions for BER July 2025 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, . Gandhi Expires 23 January 2026 [Page 8] Internet-Draft PCEP Extensions for BER July 2025 [RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC 5440, DOI 10.17487/RFC5440, March 2009, . [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, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [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, . 8.2. Informative References [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 23 January 2026 [Page 9] Internet-Draft PCEP Extensions for BER July 2025 [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, . [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 Thank you. Author's Address Rakesh Gandhi (editor) Cisco Systems, Inc. Canada Email: rgandhi@cisco.com Gandhi Expires 23 January 2026 [Page 10]