Viop

Simple Gateway Control Protocol (SGCP)

Simple Gateway Control Protocol (SGCP) is used to control telephony gateways from external call control elements. A telephony gateway is a network element that provides conversion between the audio signals carried on telephone circuits and data packets carried over the Internet or over other packet networks.

The SGCP assumes a call control architecture where the call control intelligence is outside the gateways and is handled by external call control elements. The SGCP assumes that these call control elements, or Call Agents, will synchronize with each other to send coherent commands to the gateways under their control.

The SGCP implements the simple gateway control interface as a set of transactions. The transactions are composed of a command and a mandatory response. There are five types of commands:

• CreateConnection.
• ModifyConnection.
• DeleteConnection.
• NotificationRequest.
• Notify.

The first four commands are sent by the Call Agent to a gateway. The Notify command is sent by the gateway to the Call Agent. The gateway may also send a DeleteConnection.

All commands are composed of a Command header, optionally followed by a session description. All responses are composed of a Response header, optionally followed by a session description. Headers and session descriptions are encoded as a set of text lines, separated by a line feed character. The headers are separated from the session description by an empty line.

The command header is composed of:

• Command line.
• A set of parameter lines, composed of a parameter name followed by a parameter value.

The command line is composed of:

• Name of the requested verb.
• Transaction identifier, correlates commands and responses. Transaction identifiers may have values between 1 and 999999999 and transaction identifiers are not reused sooner than 3 minutes after completion of the previous command in which the identifier was used.
• Name of the endpoint that should execute the command (in notifications, the name of the endpoint that is issuing the notification).
• Protocol version.