SIP (Session Initiation Protocol)

Session Initiation Protocol (SIP) is an application-layer control protocol that can establish, modify, and terminate multimedia sessions such as Internet telephony calls. SIP is often used in Voice over Internet Protocol (VoIP) but it is also used with video and messaging applications. It is also used for voice phone calling over LTE (VoLTE) in mobile networks. The network elements that use the Session Initiation Protocol for communication are called SIP user agents. Each user agent (UA) performs the function of a user agent client (UAC) when it is requesting a service function, and that of a user agent server (UAS) when responding to a request. SIP is defined in RFC 3261 , 3262, 3311, 3428, 3515, 3903, 6086 and 6665.

See Melrose Labs Voice Gateway/Inbound Voice,
  Melrose Labs Voice Gateway/Outbound Voice,
  Melrose Labs Voice Gateway/Conference,
  Melrose Labs Video Conferencing

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