Generalized Labels for Lambda-Switch-Capable (LSC) Label Switching Routers
updated by
- rfc-7699 — Generalized Labels for the Flexi-Grid in Lambda Switch Capable (LSC) Label Switching Routers
- rfc-8359 — Network-Assigned Upstream Label
updates
- rfc-3471 — Generalized Multi-Protocol Label Switching (GMPLS) Signaling Functional Description
Extracted elements (20)
Channel spacing in the label format is not used to indicate LSR capability but only to specify a frequency in signaling. When wider channel spacings such as 0.2 THz are utilized, the combination of a narrower channel spacing value and the n integer can still represent the correct frequency.
RFC 3471 defined wavelength labels as having significance only between two neighbors, without global wavelength semantics. As networks composed of multi-vendor LSC equipment (ROADMs, WXCs, PXCs) require wavelength continuity across domains, a standardized label format is necessary to avoid per-vendor representations and misconfiguration during manual provisioning.
The ITU-T DWDM frequency grid uses a formula (193.1 THz + n * channel spacing) rather than an index because the grids are not numbered and change with evolving frequency spacing technology. An index would therefore not be appropriate.
For bidirectional LSP setup using GMPLS RSVP-TE across domains, the Path message must contain both an Upstream_Label object and a Label_Set object with the same wavelength label value, and the Label_Set must contain a single sub-channel matching the Upstream_Label.
RFC 6205 updates RFC 3471. The existing RFC 3471 wavelength label definition (locally significant between neighbors only) is extended by this document to define a standardized format usable across multi-vendor, multi-domain LSC networks compliant with ITU-T DWDM and CWDM grids.
In all cases except the ERO subobject special case, a node MAY select any value including zero for the Identifier field.
Once an Identifier field value is selected for an LSP, it MUST NOT change until the LSP is torn down, and the value MUST be used in all LSP-related messages (e.g., Resv messages and label RRO subobjects).
When a non-zero value is assigned to the Identifier field in a label ERO subobject, the referenced node MUST use that assigned value for the Identifier field in all corresponding LSP-related messages.
When the Identifier field in a label ERO subobject is set to zero (0), the referenced node MAY assign any Identifier field value, including zero, when establishing the corresponding LSP.
The DWDM wavelength label is a 32-bit field with four subfields: Grid (3 bits), Channel Spacing C.S. (4 bits), Identifier (9 bits), and n (16 bits, two's-complement integer). The frequency is computed as: Frequency (THz) = 193.1 THz + n * channel spacing (THz).
The Grid field (3 bits) identifies the ITU-T wavelength grid: value 0 is Reserved, value 1 is ITU-T DWDM (G.694.1), value 2 is ITU-T CWDM (G.694.2), and values 3-7 are reserved for future use.
The Identifier field (9 bits) in the lambda label format distinguishes different lasers at the same node that can transmit the same frequency. It is per-node assigned and scoped, and MAY change on a per-hop basis.
The n field (16 bits) is a two's-complement integer (positive, negative, or zero) used to compute the specific DWDM frequency or CWDM wavelength from the base value and channel spacing.
IANA added three subregistries under 'Generalized Multi-Protocol Label Switching (GMPLS) Signaling Parameters': (1) Grid subregistry (values 0-7, Standards Action), (2) DWDM Channel Spacing subregistry in GHz (values 0-15, Standards Action), and (3) CWDM Channel Spacing subregistry in nm (values 0-15, Standards Action).
The CWDM Channel Spacing subregistry initial values in nm: 0=Reserved, 1=20, 2-15=Unassigned. New values assigned by Standards Action.
The DWDM Channel Spacing subregistry initial values in GHz: 0=Reserved, 1=100, 2=50, 3=25, 4=12.5, 5-15=Unassigned. New values assigned by Standards Action.
The Grid subregistry initial values: 0=Reserved, 1=ITU-T DWDM, 2=ITU-T CWDM, 3-7=Unassigned. New values assigned by Standards Action.
RFC 6205 introduces no new security considerations beyond those of RFC 3471 and RFC 3473. For a general discussion of MPLS/GMPLS security issues, readers are referred to the MPLS/GMPLS security framework in RFC 5920.
The CWDM wavelength label shares the same 32-bit structure as DWDM: Grid (3 bits), C.S. (4 bits), Identifier (9 bits), n (16-bit two's-complement). Grid=2 for ITU-T CWDM; C.S.=1 encodes 20 nm channel spacing. Wavelength (nm) = 1471 nm + n * 20 nm.
The DWDM wavelength label is 32 bits: Grid (bits 0-2, 3 bits), C.S. (bits 3-6, 4 bits), Identifier (bits 7-15, 9 bits), and n (bits 16-31, 16-bit two's-complement integer). Grid=1 for ITU-T DWDM; C.S. values encode channel spacing in GHz (1=100, 2=50, 3=25, 4=12.5).