B.2. VoIP Protocols

The mechanism for carrying a VoIP connection generally involves a series of signaling transactions between the endpoints (and gateways in between), culminating in two persistent media streams (one for each direction) that carry the actual conversation. There are several protocols in existence to handle this. In this section, we will discuss some that are important to VoIP in general and to Asterisk specifically.

B.2.1. IAX (The “Inter-Asterisk eXchange” Protocol)

If you claim to be one of the folks in the know when it comes to Asterisk, your test will come when you have to pronounce the name of this protocol. It would seem that you should say “eye-ay-ex,” but this hardly rolls off the tongue very well.^[246] Fortunately, the proper pronunciation is in fact “eeks.”^[247] IAX is an open protocol, meaning that anyone can download and develop for it.^[248]

^[246] It sounds like the name of a Dutch football team.

^[247] Go ahead. Say it. That sounds much better, doesn’t it?

^[248] Officially, the current version is IAX2 (officially standardized by the IETF in RFC 5456), but all support for IAX1 has been dropped, so whether you say “IAX” or “IAX2,” it is expected that you are talking about version 2.