OSPF Traffic Engineering (OSPF-TE) Link Availability Extension for Links with Variable Discrete Bandwidth
Extracted elements (14)
The availability parameter (a time-scale proportion of operating time at which a requested bandwidth is ensured) is used instead of a simple bandwidth value because different service types require different availability guarantees — voice typically needs 'five nines' while non-real-time services may accept lower availability — necessitating multiple <availability, bandwidth> pairs per link.
This document deliberately covers only the distribution mechanism for availability information via OSPF-TE; methods for measuring availability or using the distributed data for route computation are explicitly out of scope, with the expectation that technology-specific documents will address those aspects.
The Availability SCSI-TLV is defined as a Generalized SCSI-TLV per RFC 8258 and is carried within the ISCD defined in RFC 4202/4203. The signaling extension to support LSP provisioning over links with variable discrete bandwidth is defined separately in the companion RSVP-TE document (draft-ietf-ccamp-rsvp-te-bandwidth-availability).
A node advertising an interface with a Switching Capability that supports variable discrete bandwidth SHOULD contain one or more Availability SCSI-TLVs in its OSPF-TE LSA messages, each providing bandwidth capacity for a specified availability level.
Only one Availability SCSI-TLV for a specific availability level SHOULD be sent. If multiple TLVs are present, the one with the lowest bandwidth value SHALL be processed. TLVs with invalid values (e.g., availability >= 1) MUST be ignored.
The absence of the Availability SCSI-TLV in an ISCD that has been defined to support it SHALL be interpreted as representing a fixed-bandwidth link with the highest availability value.
The Availability level field value MUST be less than 1. It is a binary32-format floating-point number (IEEE 754-2008) transmitted in network byte order, typically expressed as 0.99, 0.999, 0.9999, or 0.99999.
The Availability SCSI-TLV MUST NOT be sent in ISCDs with Switching Capability field values that have not been defined to support it; non-supporting nodes would interpret such an ISCD/LSA as malformed.
The Availability SCSI-TLV is a new type of Generalized Switching Capability-Specific Information TLV that carries <availability, bandwidth> pairs for links with variable discrete bandwidth (e.g., microwave, copper). It is carried in OSPF-TE LSA messages and can appear one or more times per ISCD.
IANA registered two new values in the 'Switching Types' registry: value 5 ('PSC with GSCSI support') and value 52 ('L2SC with GSCSI support'), both referencing RFC 8330, to support use of the Availability SCSI-TLV.
IANA updated the 'Generalized SCSI TLV Types' registry (established by RFC 8258) to include Type 0x000A (Availability) for Switching Types 5 and 52, as defined by RFC 8330.
RFC 5920 (Security Framework for MPLS and GMPLS Networks) covers security threats, defensive techniques, monitoring, detection, and reporting requirements that apply to this extension.
Tampering with GMPLS-TE LSAs carrying Availability SCSI-TLVs may affect TE computations. RFC 3630 and RFC 2154 (OSPF with Digital Signatures) mechanisms should be used to secure and/or authenticate the information in Opaque LSAs. An OSPF security analysis is provided in RFC 6863.
The Availability SCSI-TLV has Type=0x000A (16 bits), Length (16 bits), Availability level (32-bit IEEE binary32 floating-point, network byte order, must be less than 1), and LSP Bandwidth at Availability level n (32-bit IEEE floating-point, network byte order, units are bytes per second).