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SGCP - Simple Gateway Control Protocol

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When developing Internet Telephony solutions, we came accross the need to distribute the Internet telephony gateway functionalities between the actual gateways, that perform translation between voice signals and IP packets, and a server that we call the "call agent," which would handle complex signalling protocols such as SS7-ISUP. We designed SGCP to handle the communication between the call agent and the gateways.

(picture showing the roles of SGCP, ISUP, H.323 and SIP)

SGCP is primarily designed as a simple "remote control" protocol, that the call agent uses to program gateways according to instructions received through signalling protocols such as ISUP, H.323 or SIP. We are currently defining version 1.1, which will allow for control of voice gateways, network access servers, and unified servers that comnine the two functionalities.

The main emphasis of SGCP is simplicity and reliability:

  • keeping the gateways simple, by concentrating programming difficulties in the call agent,
  • keeping the protocol simple, by limiting its role to the specific case of gateway control.
  • keeping the implementation simple, by chosing text encodings.

At the same time, we have made sure that our design allows for arbitrarily reliable and scalable designs. SGCP is a simple client-server protocol implemented on top of UDP. In case of call agent failure, a spare system can take over without any call interruption.

We believe that SGCP will allow the development of reliable and inexpensive systems. The specifications are openly available, in particular through this page. If you are interested in this information, you may want to:

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