IAX protocol

IAX2 — Inter-Asterisk eXchange protocol — protocol of VoIP data exchange between Asterisk IP-PBX systems.
Has better support for NAT traversal: unlike SIP and H.323, uses single port 4569 of UDP protocol for signalling and media, while the latter use different ports for these purposes.
This protocol allows to significantly save network bandwidth when compared with SIP, because of signalling information traversal is binary and and not text.
Also protocol allows to combine several voice streams and transmit them inside single trunk, decreasing overhead which are caused by transmitting IP header per packet.

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