IS-IS, OSPF, and BGP-LS Extensions for Advertising Bit Error Rate Metric for Traffic Engineering

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 the Bit Error Rate (BER) and Packet Error Rate (PER) of the links using measurement packets. for IS-IS, for OSPF, and for BGP-LS, define Traffic Engineering (TE) metrics extensions for advertising latency, loss, and bandwidth metrics. In this document, IS-IS, OSPF, and BGP-LS extensions are defined to advertise the BER and PER metrics for the links in the network that can be used for TE. Additionally, IS-IS, OSPF and BGP-LS extensions are defined to advertise anomaly state that can be used to avoid the links with anomaly state in path computation. Note that the mechanisms for measuring bit errors or acting on that information, once advertised, are outside the scope of this document.

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 when, and only when, they appear in all capitals, as shown here.

BER: Bit Error Rate EMA: Exponential Moving Average PER: Rate of Packets with Bit Errors TLV: Type-Length-Value

In this document, IS-IS, OSPF, and BGP-LS extensions are defined to advertise the BER and PER metrics for the links in the network that can be used for TE. Additionally, IS-IS, OSPF, and BGP-LS extensions are defined to advertise anomaly state that can be used to avoid the links with anomaly state in path computation. The PER metric can be added in the existing packet loss metric (instead of using it as a separate metric). However, the PER metric can provide different characteristics of the network, since, depending on the BER pattern (bursty or single), there can be high BER but low packet loss, and vice versa. Editor's note: The BER and PER metrics of the links can be used as generic metrics in IS-IS, OSPF and BGP-LS. However, this does not support anomaly state advertisement.

IS-IS, OSPF, and BGP-LS extensions are defined to advertise BER and PER metrics as well as anomaly state as follows. A bit: This field represents the Anomalous (A) bit. The A bit is set when the measured value of this parameter exceeds its configured maximum threshold. The A bit is cleared when the measured value falls below its configured reuse threshold. If the A bit is cleared, the sub-TLV represents steady-state link performance. Unit for BER and PER Metrics: This 24-bit field carries BER or PER as a percentage over a configurable interval. The basic unit is 0.000003%, where (2^24 - 2) is 50.331642%. This value is the highest percentage that can be expressed (the assumption that high-speed links with over 50% BER/PER are unusable). Measured values that are larger than the field maximum MUST be advertised as 0xFFFF FF. EMA: The BER metric advertised is the exponential moving average (EMA) of the BER in order to suppress the frequent advertisements. Similarly, the PER metric advertised is the exponential moving average (EMA) of the PER. Threshold: The BER metric is only advertised when user-configured threshold is crossed. Similarly, the PER metric is only advertised when user-configured threshold is crossed.

IS-IS extensions for TE are defined in . This document extends the sub-TLV structure defined in . These new sub-TLVs provide ways to advertise network-performance information related to BER and PER. The extensions in this document build on the extensions provided in IS-IS TE and GMPLS . This document defines several additional sub-TLVs for the links. Value Description ----- ---------------------------- TBA1 Unidirectional Link BER TBA2 Unidirectional Link PER Example Sub-TLV for advertising BER metric in IS-IS is shown in Figure 1.

IS-IS Unidirectional BER Metric Sub-TLV The format of the PER metric sub-TLV is the same as the BER metric sub-TLV. The Extended IS Reachability TLV (type 22) (defined in ), Inter-AS Reachability TLV (also called "inter-AS reachability information TLV") (type 141) (defined in ), and MT-ISN TLV (type 222) (defined in ) have nested sub-TLVs that permit the TLVs to be readily extended for BER and PER. This document registers new IS-IS TE sub-TLVs in the Sub-TLVs for TLVs 22, 23, 25, 141, 222, and 223.

OSPF extensions for TE are defined in . This document extends the sub-TLV structure defined in . These new sub-TLVs provide ways to advertise network-performance information related to BER and PER. This document defines several additional sub-TLVs for the links. Value Description ----- ---------------------------- TBA11 Unidirectional Link BER TBA12 Unidirectional Link PER Example Sub-TLV for advertising BER metric in OSPF is shown in Figure 2.

OSPF Unidirectional BER Metric Sub-TLV The format of the PER metric sub-TLV is the same as the BER metric sub-TLV. The BER metric advertisement is carried in Application-Specific Link Attributes Sub-TLV , which is advertised in Extended Link Opaque LSAs for OSPFv2 and E-Router-LSAs for OSPFv3.

The IGP TE metric extensions in BGP - Link State (BGP-LS) advertisement are defined in . New BGP-LS Link Attribute TLVs are defined for BER and PER. New TLV formats follow the rules defined in . Value Description ----- ---------------------------- TBA21 Unidirectional Link BER TBA22 Unidirectional Link PER Example TLV for advertising BER metric in BGP-LS is shown in Figure 3 below.

BGP-LS Unidirectional BER Metric TLV The format of the PER metric TLV is the same as the BER metric TLV.

The security considerations specified in , , and apply to the procedure and extensions defined in this document.

IANA maintains the registry for "IS-IS Sub-TLVs for TLVs Advertising Neighbor Information". IANA is requested to allocate the following sub-TLVs for types 22, 23, 25, 141, 222, and 223 from this registry. IS-IS Sub-TLV Types

Value	Description	Reference
TBA1	Unidirectional Link BER	This document
TBA2	Unidirectional Link PER	This document

The new sub-TLVs are also added in the registry "IS-IS Sub-Sub-TLV Codepoints for Application-Specific Link Attributes".

IANA maintains the registry for "Types for sub-TLVs of TE Link TLV" for OSPF. IANA is requested to allocate the following sub-TLVs from this registry. Types for sub-TLVs of TE Link TLV in OSPF

Value	Description	Reference
TBA11	Unidirectional Link BER	This document
TBA12	Unidirectional Link PER	This document

IANA maintains the registry for "BGP-LS NLRI and Attribute TLVs". IANA is requested to allocate the following TLVs from this registry. BGP-LS Attribute TLV Types

Value	Description	Reference
TBA21	Unidirectional Link BER	This document
TBA22	Unidirectional Link PER	This document