IAX versus SIP, which is better?


Over on VoIPDaily, I posted this item about VoicePulse carrying nearly 20 Million VoIP Minutes Using IAX2 Protocol. IAX2 stands for the Inter-Asterisk Exchange (IAX) protocol. It is used as a primary protocol for Asterisk, the open source PBX developed by Digium. IAX is used on Voice-over-IP networks much like the widely known SIP protocol. “Although the amount of traffic we carry using IAX is small compared to SIP,” said Ravi Sakaria, VoicePulse’s President and CEO. In his opinion, this is a significant milestone because it shows that IAX can be used in carrier class networks. Wanting to know more about IAX, I pinged Ravi, and asked him if IAX was a better option than SIP, and if yes why? His reply, “Our feeling is not that one protocol is better than the other in *all* cases (keep in mind the fact that IAX still accounts for a small percentage of the total traffic we transport), but rather that IAX has benefits in certain circumstances.” And the reasons for this are as follows:

  • IAX handles Network Address Translation at the protocol layer so it’s much easier to configure on residential connections (SIP requires using STUN, keepalives, or some other workaround not built into the protocol).
  • IAX is well suited for trunks carrying many simultaneous calls because it multiplexes the signaling for all these separate calls into one stream.  The result is that the bandwidth required is reduced significantly. 
  • IAX is the native protocol of Asterisk, so it’s very easy for people who want to use this free, open-source PBX software to use it.

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