There are three primary signalling protocols for VoIP:
H.323:
A family of protocols created by the ITU with a goal of enabling the functions needed by carriers to provide not only a service similar to that of the PSTN but also one- and two-way video distribution.
Session Initiation Protocol (SIP):
This is the latest version of signaling and has dominated development work since about 2000. All new products support it, and it attracts the most interest in the market. SIP came originally from the IETF and shows many characteristics of Internet formats such as HTML and XML. Eventually the ITU joined in the development and standardization of SIP, so it now is a joint responsibility of the IETF and ITU.
Media Gateway control protocol:
Its also known as Megaco and H.225 have narrower applicability. The management of media gateways (MGWs) that connect the PSTN or other circuit-switched voice networks to an IP or VoIP network. This protocol is used by both SIP and H.323 controllers. ITU has taken responsibility for Megaco. Some vendors predict SIP extensions will replace it.
H.323:
A family of protocols created by the ITU with a goal of enabling the functions needed by carriers to provide not only a service similar to that of the PSTN but also one- and two-way video distribution.
Session Initiation Protocol (SIP):
This is the latest version of signaling and has dominated development work since about 2000. All new products support it, and it attracts the most interest in the market. SIP came originally from the IETF and shows many characteristics of Internet formats such as HTML and XML. Eventually the ITU joined in the development and standardization of SIP, so it now is a joint responsibility of the IETF and ITU.
Media Gateway control protocol:
Its also known as Megaco and H.225 have narrower applicability. The management of media gateways (MGWs) that connect the PSTN or other circuit-switched voice networks to an IP or VoIP network. This protocol is used by both SIP and H.323 controllers. ITU has taken responsibility for Megaco. Some vendors predict SIP extensions will replace it.
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