Simple Gateway Control Protocol
SGCP was developed by Telcordia Technologies and came to fruition in early 1998. It was designed to offload the call signaling process from Gateways to a server on an IP network taking on the roll of Call Agent. While the Gateway handles translation between the IP network and the SCN, the Call Agent uses SGCP over UDP to act as a remote control, programming the gateway with call controll information received inside the network from other signaling protocols, and from outside the network (SCN) using an SS7/ISUP signaling Gateway.
Being that UDP is a fast but unreliable transport mechanism, the developers provided for failover by allowing for multiple Call Agents in the network, capable of taking over an existing connection without interruption. SGCP is a text based protocol and uses the Session Description Protocol (SDP), as does SIP. The Call Agent can get its call control information from SIP, or the H.323 protocol.
The protocol was designed keeping the KISS philosophy very much in mind (keep it simple stupid!). Implementation is simplified through the use of text encodings, and the protocol itself is kept simple by limiting its function strictly to gateway control. The role of the gateway is reduced to just translating, while the Call Agent handles the programming.
SGCP and the Physically Decomposed Gateway Model
The VoIP Signaling Protocols
H.323 | SGCP | MGCP | Megaco-H.248 | SIP
