SIP vs IAX: Difference and Comparison

Mark Spencer (Founder of Asterisk) created the IAX standard to address some of the shortcomings of the SIP standard. Later, an improved edition of IAX, known as IAX2, was released.

Compared to SIP, IAX is far more effective in terms of capacity utilization; assuming a particular throughput, IAX allows you to conduct more simultaneous telephone conversations than SIP.

Key Takeaways

  1. SIP, or Session Initiation Protocol, is widely used for voice and video communication, while IAX, or Inter-Asterisk eXchange, primarily supports VoIP (Voice over IP) calls.
  2. IAX uses a single UDP port for communication, making it easier to manage firewalls, whereas SIP requires multiple ports for signalling and media.
  3. IAX is limited to the Asterisk PBX system, while SIP enjoys broader compatibility with various devices and platforms.


The difference between SIP and IAX is that IAX is far more productive regarding bandwidth use than SIP. Given a certain amount of bandwidth, IAX allows you to carry more simultaneous private communications than SIP. IAX does this by being a digital communication rather than a plain-text interface such as SIP.


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SIP is a protocol that is used in VoIP services to begin, manage, and terminate audiovisual interaction engagements. SIP protocols enable audio, multimedia, and message apps to signal and manage each other.

Hosted SIP Trunking is supplied by a dedicated Unified Communications provider, who might also supply VoIP as well as Unified Communications as a Service (UCaaS).

IAX is a framework for establishing collaborative client encounters. IAX is comparable to SIP. Mark Spencer created IAX as a strong, user-friendly replacement to SIP, MGCP, as well as RTP.

IAX is ideal for controlling and transmitting multimedia applications as well as VoIP. IAX is flexible to practically any sort of data transport since it operates effectively with all formats.

Comparison Table

Parameters Of ComparisonSIPIAX
The use of Bandwidth It is lesser effective in terms of bandwidth use.It is highly efficient and effective for bandwidth use.
UsesIn terms of usability, it is extremely highly regarded.In terms of use, it is not common.
Structural rigidityIt is the least durable.It is extremely durable.
ExpansionIt is extensible. It includes an expansion capability.It can never be prolonged. It lacks an expansion capability.
Assault on supply depletionIt is not susceptible to such an assault.It is particularly susceptible to such an assault.

What is SIP?

The Session Initiation Protocol (SIP) is a signalling protocol that supports VoIP by specifying the messages delivered between terminals and handling the actual aspects of a conversation.

Voice conversations, unified communications, text messaging, and multimedia delivery are all supported via SIP. 

SIP is only one technique of delivering VoIP; its fundamental advantage is that it offers a real link between personal or regional telecommunications networks (PBXs) and the general phone network.

People and corporations can connect without the need for a traditional home phone in this manner. 

VoIP is a series of techniques that allow you to transmit and receive voice communications over the web.

SIP is an application layer protocol that is used to transport various types of digital data, including voice messages—as such, and SIP is a specialized technology that facilitates VoIP conversations.

A SIP trunk connects two zones of the Unified Communication system. 

By establishing these links, SIP wiring enables us to divide the system into formal and informal areas. Open names are administered by Internet telephone service providers (ITSPs), whereas privatized sites are linked to somebody’s private server.

SIP trunking is used by ITSPs to securely offer phone and live video services to subscribers who have a personal trunk connection.

What is IAX?

IAX, which stands for Inter-Asterisk eXchange, is the original Asterisk PBX standard that is currently implemented by a wide range of VoIP systems.

It offers several benefits over SIP, notably spectrum conservation, the usage of one UDP port, 4569, which allows it to pass via NAT easily, and the fact that it is a binary protocol makes it extremely hard to exploit. 

Despite these benefits, IAX is not as extensively adopted as SIP, and it places a greater burden on your system since all communication must transit via the server.

IAX is a unique VoIP solution that offers various benefits, particularly while using a limited bandwidth connection to the internet.

 IAX employs just one channel for both signalling and multimedia content, making it far less resource-intensive. Furthermore, IAX uses the Password Authentication Protocol rather than IP for identity verification. It is compatible with NAT and firewalls. 

Finally, the IAX configuration includes codecs, making it simple to make global calls while sparing your finances and the bother of holding them accountable.

The biggest disadvantage of IAX is that it is designed on top of the Asterisk operating system, therefore, you must utilize an Asterisk router with it. Asterisk is an open-source technology platform built on major private systems.

Main Differences Between SIP and IAX

  1. IAX is much faster on the line than SIP for any number of calls and any codec. 
  2. IAX explicitly isolates Caller*ID from the user’s access control. Unless Remote-Party-ID is utilized, SIP does not offer a clear means for doing this.
  3. SIP is an Internet Engineering Task Force (IETF) standard. While there is some preliminary information courtesy of Frank Miller, IAX is not yet a related framework.
  4. IAX enables an endpoint to validate a mobile number to determine whether it is full, maybe comprehensive, or finished but maybe larger. In SIP, there is no way to enable this entirely.
  5. IAX contains a distinct layer 2 and layer 3 segregation, which means that both signalling and music have distinct states. SIP does not possess such a method, and its signalling dependability is quite poor and clunky.

Last Updated : 13 July, 2023

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