Signaling Extensions for Wavelength Switched Optical Networks
Extracted elements (23)
Distributed wavelength assignment (R+DWA) is supported to enable fast provisioning during equipment failure recovery, where quick recovery is critical. Allowing selection of a specific distributed WA method is beneficial when more than one algorithm is implemented along the path.
The WSON Processing Hop Attribute TLV is encoded as an attributes TLV per RFC 5420 and carried in ERO/RRO Hop Attributes subobjects per RFC 7570, reusing existing GMPLS per-hop attribute machinery rather than defining a new signaling object, allowing targeted per-node configuration along an LSP.
This document explicitly does not address signaling information related to optical impairments (Section 3.5), scoping the extensions to signal characterization, per-node processing configuration, bidirectional LSPs, and distributed wavelength assignment method selection only.
Optical tributary signal characteristics — modulation format, FEC type, and center frequency (wavelength) — can change as a WSON signal traverses regenerators, OEO switches, or wavelength converters. These are summarized in the Optical Interface Class (RFC 7446) and must be conveyed in signaling for compatibility checking.
The WavelengthSelection sub-TLV absence is equivalent to specifying WA Method value 0 (unspecified/any), ensuring backward compatibility with nodes that do not include the sub-TLV at all.
At least one ResourceBlockInfo sub-TLV MUST be present in the WSON Processing Hop Attribute TLV. No more than two ResourceBlockInfo sub-TLVs SHOULD be present, and any present sub-TLVs MUST be processed in the order received.
Each sub-TLV MUST be padded with zeros to ensure four-octet alignment, and sub-TLV ordering is significant and MUST be preserved. Error processing follows RFC 7570.
For bidirectional LSPs, there MUST be either (a) one ResourceBlockInfo sub-TLV with both I and O bits set to 1, or (b) two sub-TLVs — one with only the I bit set and the other with only the O bit set. Any violation SHALL be treated as an error per RFC 7570.
If a receiving node does not support the requested WA method, it MUST generate a PathErr with Error Code 'Routing Problem' (24) and error sub-code 'Unsupported Wavelength Assignment value' (108).
LSPs signaled through extensions defined in this document MUST apply: Switching Capability = WSON-LSC (RFC 7688), Encoding Type = Lambda (RFC 3471), and Label Format as defined in RFC 6205.
Once a node properly parses a ResourceBlockInfo sub-TLV in an ERO Hop Attributes subobject, it allocates the indicated resources for the LSP. The node SHOULD report compliance by adding an RRO Hop Attributes subobject with the WSON Processing Hop Attribute TLV indicating the utilized resources.
Once a node properly parses the WavelengthSelection sub-TLV in an ERO Hop Attributes subobject, it uses the indicated wavelength assignment method for the LSP at that hop, and SHOULD report compliance via an RRO Hop Attributes subobject.
Only the first RB Identifier listed in the RB Set field SHALL be processed; any others SHOULD be ignored. For unidirectional LSPs, only one ResourceBlockInfo sub-TLV SHALL be processed and the I/O bits can be safely ignored.
The WA Method field defines four values: 0 = unspecified/any (implied when sub-TLV is absent), 1 = First-Fit (lowest-index available wavelength), 2 = Random, 3 = Least-Loaded (largest residual capacity, for multi-fiber networks). Values 4–127 are unassigned.
The WSON Processing Hop Attribute TLV (type value 4) is carried in ERO and RRO Hop Attributes subobjects and processed per RFC 7570 procedures. It carries one or more sub-TLVs targeting specific nodes along an LSP for optical signal processing configuration.
Two sub-TLV types are defined: ResourceBlockInfo (type 1, variable length) carrying optical interface class and processing capabilities, and WavelengthSelection (type 2, fixed 8 octets with 2-octet padding) indicating wavelength assignment directionality and method.
IANA assigned two new sub-codes in the existing 'Sub-Codes - 24 Routing Problem' registry under rsvp-parameters: 107 = 'Unsupported WavelengthSelection symmetry value' and 108 = 'Unsupported Wavelength Assignment value'.
IANA assigned type value 4 in the existing 'Attributes TLV Space' registry (rsvp-te-parameters) for the WSON Processing Hop Attribute TLV, allowed only on RO LSP Attribute Subobject (not on LSP_ATTRIBUTES or LSP_REQUIRED_ATTRIBUTES).
IANA created a new registry 'Sub-TLV Types for WSON Processing Hop Attribute TLV' under rsvp-te-parameters with entries: 0 = Reserved, 1 = ResourceBlockInfo, 2 = WavelengthSelection. Future assignments require Standards Action or Specification Required.
IANA created a new registry 'Values for Wavelength Assignment Method field in WavelengthSelection Sub-TLV' under rsvp-te-parameters with values 0 (unspecified), 1 (First-Fit), 2 (Random), 3 (Least-Loaded multi-fiber), and 4–127 (Unassigned).
This document builds on RFC 3473 mechanisms and only differs in the specific information communicated (optical resource and wavelength selection properties). The additional information is not considered to substantively change or add to the security considerations of existing GMPLS signaling; RFC 5920 provides an overview of GMPLS control plane security.
Each sub-TLV within the WSON Processing Hop Attribute TLV uses an 8-bit Type field, 8-bit Length field (total octets including Type and Length), a variable-length Value field, and variable Padding to ensure 4-octet alignment.
The WavelengthSelection sub-TLV value field is 32 bits: W bit (1 bit) indicating whether same or different wavelengths are required in both directions, WA Method (7 bits) specifying the wavelength assignment algorithm, and Reserved (24 bits).