Generalized Labels for the Flexi-Grid in Lambda Switch Capable (LSC) Label Switching Routers
updates
Extracted elements (17)
The flexi-grid is anchored at 193.1 THz with a 6.25 GHz nominal central frequency granularity and 12.5 GHz slot width granularity, per ITU-T G.694.1. Implementations are not required to support every possible slot width or position; subsets are explicitly allowed, enabling deployment flexibility.
The flexi-grid label format is intentionally modeled on the fixed-grid label defined in RFC 6205 so that the first 32 bits remain backward compatible with RFC 6205 implementations; a legacy node will recognize the format of the first word even if it cannot interpret the new grid type value.
The m parameter is both a label property (defines what is switched) and a bandwidth parameter; it appears in both the GMPLS flexi-grid label and in the SENDER_TSPEC/FLOWSPEC objects. This overlap is an inherent consequence of flexi-grid's variable-width spectrum allocation.
A legacy management system expecting 32-bit lambda labels will not fail ungracefully when encountering 64-bit flexi-grid labels because the first 32 bits follow the RFC 6205 format. Migration can be done in two steps: first handle 64-bit label length, then add full field-level parsing.
GMPLS assumes both ends of a link know which label types are supported. A legacy node receiving an unknown flexi-grid label will attempt to process it as a known label type, potentially yielding a poor outcome; thus, flexi-grid labels must not be used with legacy nodes that do not support them.
An implementation using the flexi-grid label encoding MUST follow RFC 3473 and RFC 3471 (as updated by RFC 6205), MUST set Grid to 3 and C.S. to 5, MUST set Identifier to indicate the local laser identifier, MUST set n per the frequency formula, and MUST set m per the slot width formula.
Component labels in a compound label MUST be presented in increasing order of the value n. Implementations MUST NOT infer anything about the encoding of a signal into the set of slots from the label itself.
The compound label mechanism MUST NOT be used for groupings other than adjacent slots of identical width in increasing frequency order unless and until those forms are defined and documented in ITU-T Recommendations.
The Reserved field in the flexi-grid label MUST be set to zero on transmission and SHOULD be ignored on receipt.
Composite channels can alternatively be constructed from individual LSPs using single flexi-grid slots managed as a group (analogous to RFC 6344 for TDM), without requiring compound labels; in this case, standard single-slot labels suffice and no additional label definitions are needed.
The flexi-grid label defines a new Grid value of 3 ('ITU-T Flex') to supplement existing values in RFC 6205, and a new C.S. value of 5 to represent 6.25 GHz nominal central frequency granularity.
The m field in the flexi-grid label is a 16-bit integer encoded in line format that identifies slot width according to the formula: Slot Width (GHz) = 12.5 GHz * m. It determines both the label identity and the bandwidth supported by the LSP.
The n field (inherited unchanged from RFC 6205) is a two's-complement integer used to compute the central frequency as: Frequency (THz) = 193.1 THz + n * 0.00625 THz for the flexi-grid, identifying the nominal central frequency of the slot.
IANA allocated a new entry in the GMPLS Signaling Parameters 'DWDM Channel Spacing' subregistry: Value 5 = 6.25 GHz, referencing RFC 7699.
The definition of the new flexi-grid label encoding does not introduce any new security considerations beyond those in RFC 3471 or RFC 3473. For general MPLS/GMPLS security, RFC 5920 applies.
A compound label for virtual concatenation is a LABEL object formed by concatenating r 64-bit Flexi-Grid Labels, with object length (4 + 8r) bytes. The component labels are ordered by increasing n value, and Grid must be 3 and C.S. must be identical in each component.
The Flexi-Grid Label is a 64-bit encoding with fields: Grid (3 bits), C.S. (4 bits), Identifier (variable), n (16-bit two's-complement integer for central frequency), m (16-bit integer for slot width), and Reserved (set to zero on transmission). This extends the 32-bit fixed-grid lambda label defined in RFC 6205.