IAX

IAX is the short form of complete term Inter-Asterisk exchange. Actually IAX is the primary Asterisk PBX protocol. Nowadays it is supported by many VoIP setups. This is advantageous than SIP in a number of ways like bandwidth efficiency. It is used a single UDP port 4569. Thus it works via NAT quite easily.  Moreover, it is a binay protocol therefore, it is safer from attacks. However, despite of aforesaid merits, IAX is not considered the ideal SIP. It also throws load on the servers as in this technique all the traffic passes through the server.