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Asterisk is one of the oldest and most stable telecommunication products ever released along with [Kamailio SIP Server] and [Freeswitch. Asterisk does so with the help of its AGI interface. AGI provides an interface between the Asterisk dial plan and an external program that wants to manipulate a channel in the dial plan. In general, the interface is synchronous - actions are taken on a channel from an AGI block and do not return until the action is completed.