SCCP (Skinny Client Control Protocol) ALGs

Skinny Client Control Protocol (SCCP) is a Cisco proprietary protocol for call signaling. Skinny is based on a call-agent-based call-control architecture. The control protocol uses binary-coded frames encoded on TCP frames sent to well-known TCP port number destinations to set up and tear down RTP media sessions.

The SCCP protocol, in the same way as other call control protocols, negotiates media endpoint parameters?specifically the Real-Time Transport Protocol (RTP) port number and the IP address of media termination?by embedding information in the control packets. The SCCP Application Layer Gateway (ALG) parses these control packets and facilitates media and control packets to flow through the system.