SIP vs IAX2 phones in VICIdial

When you add a phone in VICIdial, the Client Protocol field offers a few choices, and two of them dominate everyday use. SIP and IAX2 are both ways for a phone to talk to the dialer, but they behave differently on the wire. Most softphones and desk phones speak SIP, while IAX2 shows up more often when you are linking two servers together. Picking the right one keeps registration clean and the audio flowing.

What SIP is

SIP, short for Session Initiation Protocol, is the language nearly every modern phone uses to set up a call. When you choose SIP (Session Initiation Protocol) as the protocol, VICIdial builds the matching account on Asterisk automatically, usually within a minute of saving the form. The phone extension you enter becomes the device name, so for a phone Asterisk knows as SIP/test101 you would type test101 in the field and leave out the slash. SIP entries should not contain dashes.

SIP is the safe default for a desk phone, a Softphone, or a browser-based Webphone. If you are not sure which to use, SIP is almost always the answer.

What IAX2 is

IAX2 is the Inter-Asterisk eXchange protocol, designed by the Asterisk project itself. Its signature trick is carrying both the signalling and the audio on a single UDP port, which makes it friendlier when a firewall sits in the way. With IAX2, a name like IAX2/IAXphone1@IAXphone1 means you enter IAXphone1 in the phone extension and set the protocol to IAX2. Like SIP entries, IAX2 names should avoid dashes.

You will most often reach for IAX2 when tying servers together rather than for individual agent handsets, because hardware phones speaking IAX2 are uncommon today.

The single-port behaviour is the practical reason IAX2 still shows up. SIP keeps its signalling and its audio on separate streams, which works fine on an open network but can trip over firewalls and address translation that handle each stream differently. IAX2 bundles everything together, so there is one path to allow through and fewer surprises when the phone sits behind a router that rewrites addresses. That said, the same single-stream design is also why fewer manufacturers ship IAX2 desk phones, and why support for it is thinner across the wider phone market. For a normal agent seat you trade that firewall friendliness for the much larger ecosystem that has grown up around SIP.

Choosing between them

flowchart TD
  A[New phone] --> B{What is the device}
  B -->|Desk phone or softphone| C[Pick SIP]
  B -->|Browser webphone| C
  B -->|Server to server link| D[Pick IAX2]
  C --> E[Asterisk account auto-built]
  D --> E
  E --> F[Device registers and rings]

What stays the same either way

Whichever protocol you choose, the rest of the phone entry works identically. You set an Extension, a dialplan number, a Server IP, and a Registration Password, and the account appears on the chosen server about a minute later. The registration password is the secret your device uses, and it is the field people most often confuse with the agent login password. They are separate.

• SIP: the everyday default for handsets, softphones, and webphones.
• IAX2: handy across firewalls and for linking servers, less common on individual phones.
• Both build their account automatically once you save.

If you want the full field-by-field tour, the phones pillar guide covers the whole form, and the Client Protocol guide helps when EXTERNAL or PJSIP also enter the picture.

On a hosted dialer the SIP setup is handled for you and a fresh box is live in under 40 seconds, so you can register a phone and start dialing the same day. See VICIfast plans to compare what each tier includes.