Skinny Call Control Protocol
The Skinny Client Control Protocol (SCCP, or short Skinny) is a proprietary network terminal control protocol originally developed by Cisco.
The SCCP technology is now owned and defined by Cisco Systems. SCCP is a lightweight protocol for session signaling with Cisco Unified Communications Manager (formerly called CallManager). SCCP is used to communicate between IP devices and Cisco Unified Communications Manager.  Examples of SCCP clients include the Cisco 7900 series of IP phones, Cisco IP Communicator softphone and the 802.11b wireless Wireless IP Phone 7920, along with Cisco Unity voicemail server. CallManager acts as a signaling proxy for call events initiated over other common protocols such as H.323, Session Initiation Protocol (SIP), ISDN and/or MGCP.
A SCCP 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.
Some Cisco Analog gateways, such as the VG248 gateway, register and communicate with Cisco Unified Communications Manager using SCCP.
Cisco acquired SCCP technology when it acquired Selsius Corporation in 1998. For this reason the protocol is also referred to in Cisco documentation as the Selsius Skinny Station Protocol. Another remnant of the origin of the Cisco IP phones is the default device name format for registered Cisco phones with CallManager. It 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 and FreeSWITCH systems. IPBlue markets a software phone (soft phone) which uses SCCP for signaling and emulates a Cisco 7960 hardware phone. Twinlights Software distributes a soft phone implementation for Android based devices. The Cisco Unified Application Environment, the product acquired by Cisco when they purchased Metreos supports using SCCP to emulate Cisco 7960 hardware phones allowing applications to access all Cisco line-side features.