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).

Session-Initiation Protocol. A signaling protocol used for establishing sessions in an IP network. A session could be a simple, two-way telephone call, or it could be a collaborative multi-media conference session.

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

Network Protocol Data Intelligence. Also called “Interworking,” it is a software product that operates within Excel’s Call Control (Layer 4) and Services (Layer 5) call processing layers. NPDI is meant to enhance Excel’s call processing product offering by allowing call processing layers (specifically Layers 4 and 5) to perform advanced analysis, generation, and conversion of Network Signaling (NS) Layer 3 information.

See Information Control Block.