The Skinny Call Control Protocol (SCCP, or short Skinny) is a proprietary network terminal control protocol originally developed by Selsius Corporation.
The SCCP technology is now owned and defined by Cisco Systems, Inc. as a messaging system between a Skinny client and the Cisco CallManager. Examples of skinny clients include the Cisco 7900 series of IP phones, Cisco IP Communicator softphone and the 802.11b wireless Cisco 7920, along with Cisco Unity voicemail server. Skinny is a lightweight protocol which allows for efficient communication with Cisco CallManager. CallManager acts as a signaling proxy for call events initiated over other common protocols such as H.323, SIP, ISDN and/or MGCP.
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A Skinny client uses TCP/IP to communicate with one or more Call Manager applications in a cluster. It uses the Real-time Transport Protocol (RTP) over UDP-transport for the bearer traffic (real-time audio stream) with other Skinny clients or an H.323 terminal. SCCP is a stimulus-based protocol and is designed as a communications protocol for hardware endpoints and other embedded systems, with significant CPU and memory constraints.
Cisco acquired SCCP technology when it acquired Selsius Corporation in 1998. As a remnant of the Selsius origin of the current Cisco IP phones, the default device name format for registered Cisco phones with CallManager is SEP -- as in Selsius Ethernet Phone -- followed by the MAC address. Cisco also has marketed a Skinny-based softphone called Cisco IP Communicator.
Other companies like Symbol Technologies, SocketIP, and Digium have implemented this protocol in VoIP Terminals (phones), Media Gateway Controllers, and Softswitches. An open source implementation is available in the Asterisk (PBX) system. IPBlue markets a software phone (soft phone) which uses SCCP for signaling and emulates a Cisco 7960 hardware phone.