IETF RFC 5140 PDF

This document describes the Telephony Gateway Registration Protocol (TGREP) for registration of telephony prefixes supported by telephony gateways and soft switches. The registration mechanism can also be used to export resource information. The prefix and resource information can then be passed on to a Telephony Routing over IP (TRIP) Location Server, which in turn can propagate that routing information within and between Internet Telephony Administrative Domains (ITADs). TGREP shares a lot of similarities with the TRIP protocol. It has similar procedures and finite state machine for session establishment. It also shares the same format for messages and a subset of attributes with TRIP.