The Simple Gateway Control Protocol was published in 1998 by Christian Huitema and Mauricio Arango, as part of the development of the "Call Agent Architecture" at Telcordia. In this architecture a central server, the "Call Agent", controls "media gateways" and receives telephony signaling requests through a "signalling gateway". (Later implementation of the architecture refer to the "Call Agent" as a "Softswitch".)
SGCP was designed to be compatible with the Session Initiation Protocol (SIP), enabling the Call Agent to relay calls between a Voice over IP network using SIP and a traditional telephone network. The SGCP commands are encoded with a syntax somewhat comparable to the SIP or HTTP headers. They carry a payload describing the voice over IP media stream. This payload is encoded using the same "session description protocol" (SDP) as SIP.
SGCP was merged with the IPDC proposal sponsored by Level3 Communications. This led to the definition of the Media Gateway Control Protocol, jointly submitted to the IETF by the authors of SGCP and IPDC in November 1998.