Tag-Length-Value block. A standardized block that allows data to inserted in a standard way into API messages.

Domain Name Server (or Service). Used to convert H.323 IDs, URLs, and e-mail IDs to IP addresses. DNS is also used to help find remote gatekeepers and to reverse-map raw IP addresses to host names of administrative domains.

Internet Protocol. Part of the TCP/IP family of protocols used to route messages and tracks the addresses of nodes.

Voice over Internet Protocol. The delivery of voice information in digital form in discrete packets rather than in the traditional circuit-committed protocols of the public-switched telephone network (PSTN).