BSS Application Part (BSSAP) is a protocol in Signaling System 7 used by the Mobile Switching Center (MSC) and the Base station subsystem (BSS) to communicate with each other using signalling messages supported by the MTP and connection-oriented services of the SCCP. For each active mobile equipment one signalling connection is used by BSSAP having at least one active transactions for the transfer of messages.
BSSAP provides two kinds of functions:
- The BSS Mobile Application Part (BSSMAP) supports procedures to facilitate communication between the MSC and the BSS pertaining to resource management and handover control.
- The Direct Transfer Application Part (DTAP) is used for transfer of those messages which need to travel directly to a Mobile equipment from MSC by passing any interpretation by BSS. These messages are generally pertaining to Mobility management (MM) or Call Management (CM).
- 3GPP TS 48.008 Mobile Switching Centre - Base Station System (MSC-BSS) interface; Layer 3 specification