0x7F SIP Stack ID

Byte | AIB Field Description
--- | ---
2 | Address Element: 0x7F
3 | Data Length: 0x04
4 | Reserved: 0xFF
5 | Stack ID: 0x00
6, 7 | Data [0,1] Call Handle. Tied to the Call ID. Used to address a particular SIP dialog. 0xFF 0xFF when querying.

See Address Information Block.
The information in an AIB that follows the header, down to the data field. An AIB can have one or more Address Elements. AEs correspond to Span, Channel, and SS7 Link.
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.