A Telephony Gateway REgistration Protocol (TGREP)
Extracted elements (27)
Consolidation (combining routes for the same destination with different attributes) is distinct from aggregation (combining routes for different destinations into a summary). Consolidation must occur before aggregation in the logical processing sequence at the Ingress LS.
Route consolidation in the Ingress LS combines multiple routes for the same destination (from different gateways) with different attributes into a single route by taking the union of attribute values. This prevents loss of routing information that would occur if only one of the per-gateway routes were selected to be presented to the Egress LS.
TGREP was created to fill gaps in TRIP: TRIP defines inter-provider telephony routing but has no mechanism for injecting routes from within a network (from gateways), nor for selecting a specific gateway when a call arrives. TGREP addresses both gaps by providing a gateway-to-LS registration protocol.
TGREP reuses TRIP message formats (OPEN, UPDATE, KEEPALIVE, NOTIFICATION) and the same FSM for session establishment. Several TRIP attributes are not applicable in TGREP (AdvertisementPath, RoutedPath, AtomicAggregate, LocalPreference, MultiExitDisc, ITADTopology, ConvertedRoute); a TGREP receiver MAY ignore them if present.
A TGREP sender MUST support all mandatory TRIP attributes when sending UPDATE messages to the TRIP Location Server.
A TGREP session MUST NOT send UPDATEs of more than one category among: (a) Prefix address families (E164, Pentadecimal, Decimal), (b) TrunkGroup address family, or (c) Carrier address family, for a given established session. Route-type specifications in the OPEN message violating this rule MUST be rejected with a NOTIFICATION message.
An LS aggregating routes to the same prefix with TotalCircuitCapacity SHOULD add the values of the individual routes to determine the aggregated route's value within the same ITAD.
It is RECOMMENDED that measures be taken to reduce messaging load when originating AvailableCircuits updates, and that a sufficiently large time window be used to provide a useful aggregated statistic.
It is RECOMMENDED that the set of gateway routes for each destination be consolidated before presenting a candidate route to the Egress LS, to maximally represent the collective routing capabilities of all managed gateways.
Routes MUST NOT be disseminated with the AvailableCircuits attribute; it is intended to reflect capacity at the originating gateway only and its highly dynamic nature makes broader dissemination inappropriate.
Routes MUST NOT be disseminated with the CallSuccess attribute; its potential to change dynamically makes it unsuitable for broader propagation.
Routes with differing Prefix attributes MUST NOT be aggregated; routes with the same Prefix attribute value MAY be aggregated with the same Prefix attribute attached.
Routes with differing TrunkGroup attributes MUST NOT be aggregated. TrunkGroup routes SHOULD NOT be disseminated external to the ITAD.
TRIP's route selection and aggregation operations MUST NOT be implemented by TGREP gateways, which operate in Send Only mode and do not run call route selection.
TGREP is a route registration protocol for telephony gateways and soft switches to advertise reachability (prefixes, trunkgroups, carriers) to a TRIP Location Server. It is syntactically identical to TRIP but differs in route processing rules, supports a 'consolidation' operation, and operates asymmetrically with gateways in Send Only mode.
The AvailableCircuits attribute (TRIP Type Code 14) is a 4-octet unsigned integer representing the current number of available PSTN circuits on a route. It is highly dynamic, changes with every call, and is used ONLY between a gateway and its peer LS.
The CallSuccess attribute (TRIP Type Code 15) is two 4-octet unsigned integers: the first is the count of successfully terminated calls, the second is the total attempted calls, both measured over a given time window. It is used ONLY between a gateway and its peer LS and MUST NOT be disseminated.
The TotalCircuitCapacity attribute (TRIP Type Code 13) is a 4-octet unsigned integer representing the total number of PSTN circuits administratively provisioned for a route. It reflects static capacity as opposed to real-time availability and MAY be propagated beyond the receiving LS.
Two new TRIP address families are defined: TrunkGroup (code 4) and Carrier (code 5). These flat (non-hierarchical) address families allow AvailableCircuits, TotalCircuitCapacity, and CallSuccess to be reported at the granularity of a trunkgroup or carrier rather than a prefix, enabling more accurate and scalable resource reporting.
RFC 5140 registers eight new TRIP Attribute Type Codes: 13 (TotalCircuitCapacity), 14 (AvailableCircuits), 15 (CallSuccess), 16 (E.164 Prefix), 17 (Pentadecimal Routing Number Prefix), 18 (Decimal Routing Number Prefix), 19 (TrunkGroup), and 20 (Carrier). These are added to the shared TRIP/TGREP IANA registry.
RFC 5140 registers two new TRIP Address Family Codes: code 4 for TrunkGroup and code 5 for Carrier. These are added to the shared TRIP/TGREP IANA Address Family registry.
Implementations SHOULD use IKEv2 for key exchange. Implementations employing IKEv2 SHOULD support 3DES-CBC for confidentiality and HMAC-SHA1 for integrity. A transport mode SA is appropriate for protecting the TRIP session between two peer LSs.
The security mechanism for TGREP peering sessions is IPsec, using AH for data origin authentication, connectionless integrity, and optional anti-replay protection, or ESP for those properties plus confidentiality. Implementations using ESP SHALL comply with RFC 4835 Section 3.1.1 minimum algorithms; implementations using AH SHALL comply with RFC 4835 Section 3.2.
The TGREP finite state machine is identical to TRIP's FSM except that when in the Established state and an UPDATE message is received, the UPDATE is silently discarded and the gateway remains in Established state. Gateways also never generate NOTIFICATION messages in response to UPDATE messages; any received UPDATE is silently discarded.
The Carrier attribute (TRIP Type Code 20) is a variable-length sequence of carrier identifiers, each a 1-octet Length plus a Value field carrying 'global-cic' or 'local-cic' per RFC 4694. For 'local-cic', the phonedigit-hex and cic-context parts are separated by ';'. A Length of 0 means the gateway can terminate ALL carriers.
The Prefix attribute (Type Codes 16/17/18 for E.164/Pentadecimal/Decimal) encodes a sequence of prefix values with no padding: each prefix is preceded by a 2-octet Length field indicating the size of the Address field in octets. A Length field of 0 for the entire attribute signifies the gateway can terminate ALL prefixes of that type.
The TrunkGroup attribute (TRIP Type Code 19) is a variable-length sequence of trunkgroup identifiers, each encoded as a 1-octet Length followed by a Value field containing a trunkgroup label and trunk context separated by ';'. A Length of 0 for the whole attribute means the gateway can terminate ALL trunkgroups.