Telephony Routing over IP (TRIP) Attribute for Resource Priority
Extracted elements (15)
The attribute is marked Independent Transitive so it is forwarded among all ITADs; a Location Server that does not recognize the attribute sets the Partial flag but still forwards it, ensuring wide dissemination of gateway capability information.
The ResourcePriority attribute advertises only the NameSpace (not the individual r-priority values within it), because the objective is to indicate which priority services a gateway supports, not to signal a specific priority level for a particular call.
TRIP was extended rather than SIP alone because TRIP is the protocol responsible for advertising gateway reachability and capabilities across ITADs; without a TRIP attribute, there was no mechanism to disseminate which gateways support a given Resource-Priority NameSpace.
The ResourcePriority attribute is based on the NameSpace.Value tuple from the SIP Resource-Priority header (RFC 4412), enabling transparent bridging of priority codepoints (e.g., ANSI T1.631-1993 NS/EP) between PSTN standards and IETF SIP/TRIP signaling.
A Location Server MAY add the ResourcePriority attribute when propagating routing objects to an LS in another domain; inclusion is a matter of local administrative policy.
A Location Server MUST include the ResourcePriority attribute when communicating with peer LSs within its own domain.
If a ResourcePriority attribute is received from a peer LS in another domain, the receiving LS MUST propagate it to other LSs within its own domain.
If a route has a ResourcePriority attribute associated with it, the originating Location Server MUST include that attribute in the advertisement it originates.
Routes with differing ResourcePriority token values MUST NOT be aggregated.
Routes with the same ResourcePriority token values MAY be aggregated, and the same ResourcePriority attribute may be attached to the aggregated object.
The NameSpace token syntax for the ResourcePriority attribute is an alphanumeric string (with allowed special characters: '-', '!', '%', '*', '_', '+', '`', "'", '~'), imported from RFC 4412 which in turn imported 'alphanum' from RFC 3261.
The ResourcePriority TRIP attribute (Type Code 12) associates one or more SIP Resource-Priority NameSpace tokens with a gateway, advertising which prioritized telephony services (e.g., GETS, GTPS) are reachable through that gateway. It is set to Not Well-Known and Independent Transitive.
IANA assigned TRIP attribute code 12 with the name 'ResourcePriority', recorded in the TRIP parameters registry at http://www.iana.org/assignments/trip-parameters.
The ResourcePriority attribute itself introduces no new direct security considerations; all security considerations for the TRIP protocol and its messages remain as articulated in Section 14 of RFC 3219.
The ResourcePriority attribute encoding consists of one or more tuples, each containing a 2-octet NameSpace Length field followed by a variable-length NameSpace Value field. There is no padding between tuples.