VoIP Protocols

When using VoIP voice is broken up into small packets which are sent over a network and reassembled into voice at the other end. In order to perform this task a network protocol is required; this describes the format of the network messages so that both ends know how to reassemble the voice. In addition to the voice, control information is also needed – this is used to tell the user that someone is calling, to accept the call and to end the call (also for holding and transferring calls etc.).

Unfortunately, there are a number of VoIP protocols around; these are described below.

• RTP – Real time protocol, used for voice transmission

• SIP – Session Initiation Protocol, used for session (call) control

• H.323 – Used for session/call control

• IAX2 – Inter-Asterisk eXchange, used for both session control and voice transmission

• Skype – Proprietary VoIP protocol