Skinny Client Control Protocol
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SCCP is a proprietary terminal control protocol originally developed by Selsius Corporation. It is now owned and defined by Cisco Systems, Inc. as a messaging set between a skinny client and the Cisco CallManager. Examples of skinny clients include the Cisco 7900 series of IP phone such as the Cisco 7960, Cisco 7940 and the 802.11b wireless Cisco 7920. Skinny is a lightweight protocol which allows for efficient communication with Cisco Call Manager which may act as a proxy for signalling of call events with other common protocols such as H.323, SIP, ISDN and/or MGCP.
A skinny client users TCP/IP to and from one or more Call Managers in a cluster. RTP/UDP/IP is used to and from a similar skinny client or H.323 terminal for the bearer traffic (real-time audio stream). 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 the late 1990's. 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.
Other companies like Symbol Technologies and SocketIP have implemented this protocol in VoIP Terminals (phones) and Media Gateway Controllers or Softswitches.
A company named IPBlue (http://www.ipblue.com/) has created a software phone (soft phone) which uses SCCP for signaling, too. This phone in fact appears to the Cisco CallManager server as a 7960 hardware phone.