How to choose between SIP Trunk, Registrar SIP, and IAX?

Different systems are available to access our VOIP services. Voice Over IP use the Internet to carry your call: the bandwidth and stability of your connection is a determining factor of call capacity and quality.

The SIP Protocol

SIP is now a standard protocol within the industry. Numerous manufacturers support it and thanks to its very comprehensive request-response structure, SIP installations are easy to debug. Indeed, SIP reuses most of the status codes of the HTTP request/response model. 

Two types of packets are exchanged during a call: media packets, carrying the communication itself (voice) and signaling packets helping to initialize the communication and maintaining it.

Trunk SIP It requires an extensive setup but offers an exhaustive control over your phone system. On the other hand, Registrar SIP is a more accessible gateway to SIP: it uses softphones, which makes the initial setup much easier than trunk SIP. 

SIP Trunk

Trunk SIP is the industry standard and ultimately provides the best call quality. SIP trunk offers a broad gateway compatibility. A fixed IP is required to use SIP trunk since it's used for authentification. Because of this reliance on IP, SIP installations can have issues while using NAT, see our FAQ entry for more details:

Getting Started / FAQ / What are the issues between NAT and VoIP?

SIP Registrar

On the other hand, SIP registrar is designed for the end-user with a lot of built-in features. Some gateways even require it. Nevertheless, it's more restricting that SIP trunk and some features are not available on Registrar SIP such as custom CLIs.

IAX Implementation

IAX (Inter-Asterisk-eXchange) is a wholly different VoIP implementation that comes with numerous advantages, especially when on using a low bandwidth internet connection.

Indeed, IAX uses only one stream for both signaling and media payloads, making it much less resource-hungry. Moreover, IAX uses the Password Authentication Protocol, it doesn't rely on IP for authentification. It supports NAT and firewalls. Finally, our IAX setup comes packed with codecs making it easy to call internationally while saving you the money and the hassle of setting them up.

IAX main downside is that it's built on top of the Asterisk software: you must use an Asterisk gateway with IAX. Asterisk is an open-source software built on top of proprietary system components 

Overview of the three VOIP implementations

Compatibility Offered by each implementation