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Difference Between SIP and IAX


Voice over Internet Protocol, or VoIP, is rapidly gaining popularity as a low-cost alternative to regular calls. Under VoIP, there are a number of other protocols that can be used which include the Session Initiation Protocol, or SIP, and Inter-Asterisk eXchange commonly known as IAX. The main difference between SIP and IAX is that IAX is a lot more efficient when utilizing bandwidth compared to SIP. This was the main reason behind the creation of IAX. Given a specific bandwidth, using IAX lets you carry a greater number of concurrent phone calls than if you used SIP.

IAX achieves this by being a binary protocol and not a plain-text protocol like SIP. Using binary lets IAX compress the commands and codes into the smallest size possible. It also means that IAX is a bit more robust than SIP, which needs a parse in order to split and recognize the different commands that are being given.

IAX is not without disadvantages as it does suffer from quite a few. The first is the difficulty in extending the IAX protocol. Because of the lack of a generic extension mechanism in IAX, it is necessary for any new additions to be added to the specification; unlike SIP which can be extended pretty easily.

The second disadvantage is the use of a single port. On one end, this is actually good because it makes network translation a virtual breeze. The downside of doing so is it makes it easier for malicious people to execute resource exhaustion or denial of service attacks. By flooding the port used by IAX, they can overcome the system and prevent legitimate users from accessing the service. Because there is no single port for SIP, this is not that large of a problem.

When it comes to usage, SIP is the more popular of the two. Virtually all VoIP clients support the use of SIP. SIP is also used by many hardware manufacturers as the main protocol for their VoIP handsets leading to the rise of the term “SIP phones.”


1.IAX is more bandwidth efficient than SIP.
2.SIP is in plain text while IAX is not.
3.IAX is not as extensible as SIP.
4.IAX vulnerable to resource exhaustion attacks while SIP is not.
5.SIP is more popular compared to IAX.

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