Asterisk Gateway Interface (AGI) is a software interface and communications protocol for application level control of selected features of the

Asterisk PBX Asterisk is a software implementation of a private branch exchange (PBX). In conjunction with suitable telephony hardware interfaces and network applications, Asterisk is used to establish and control telephone calls between telecommunication e ...

. AGI allows an external, user-written program, launched from the Asterisk dial plan via pipes to control telephony operations on its associated control and voice channels. It is similar to the CGI feature of

web server A web server is computer software and underlying hardware that accepts requests via HTTP (the network protocol created to distribute web content) or its secure variant HTTPS. A user agent, commonly a web browser or web crawler, initiate ...

s in allowing any language to be used for writing the external program which communicates with Asterisk via stdin and stdout. While the initial feature set of AGI included only a procedural control of Asterisk operations via commands and response handshake, Enhanced AGI (EAGI) also provided out-of-band access to the incoming audio stream. FastAGI is an extension to AGI which allows the external program to run at a separate network host to avoid the overhead of creating a new process for every call on the Asterisk server. It uses a

TCP TCP may refer to: Science and technology * Transformer coupled plasma * Tool Center Point, see Robot end effector Computing * Transmission Control Protocol, a fundamental Internet standard * Telephony control protocol, a Bluetooth communication s ...

socket for communication to the external host which provides the function of an AGI service, in a manner of the

client–server model The client–server model is a distributed application structure that partitions tasks or workloads between the providers of a resource or service, called servers, and service requesters, called clients. Often clients and servers communicate over ...

. The default TCP port for FastAGI is 4573. Similar to

HTTP The Hypertext Transfer Protocol (HTTP) is an application layer protocol in the Internet protocol suite model for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide Web, ...

uniform resource identifier A Uniform Resource Identifier (URI) is a unique sequence of characters that identifies a logical or physical resource used by web technologies. URIs may be used to identify anything, including real-world objects, such as people and places, conc ...

s (URIs), FastAGI employs a URI format of . The AGI feature set of Asterisk is implemented as an Asterisk loadable module (''res_agi''). The features may be access by a variety of application programming interfaces in various languages, such a
phpagi
Perl AGI Library
CAGINanoAGI
an
PyST

References

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