How to pick the right Client Protocol for a phone

The Client Protocol field tells VICIdial how a phone connects to the dialer, and it is one of the fields you must set before a new phone entry will save. The menu offers SIP, PJSIP, IAX2, Zap, and EXTERNAL. Each one means something specific, and the right answer almost always falls out of one question: what is the device. Once you know that, the menu stops being a guessing game.

The five choices in plain terms

• SIP: the everyday default for desk phones, softphones, and webphones.
• PJSIP: the newer SIP engine in Asterisk, used when your platform is built around it.
• IAX2: handy across firewalls and for linking servers, rare on individual handsets.
• Zap: for channelbank or DAHDI hardware, set up by an administrator first.
• EXTERNAL: a remote or speed-dial number that places calls through the dialplan, with no account created.

Start from the device

For a normal handset or Softphone, choose SIP (Session Initiation Protocol) unless your platform was clearly built around the newer PJSIP stack. For tying two servers together, IAX2 carries signalling and audio on one port, which is friendlier to firewalls. For analog hardware on a channelbank, Zap is the option, but the account must exist on the box before you build the phone. And when you only want to list a remote number rather than register a device, EXTERNAL is the one. The SIP, PJSIP, and IAX2 choices all generate their Asterisk account automatically within a minute of saving.

A quick decision path

flowchart TD
  A[What is the device] --> B{Registers to the server}
  B -->|Yes softphone or deskphone| C[SIP or PJSIP]
  B -->|Yes server to server| D[IAX2]
  B -->|Yes analog channelbank| E[Zap]
  B -->|No it is a remote number| F[EXTERNAL]
  C --> G[Account auto-built]
  D --> G
  E --> H[Admin sets up first]

Match the protocol to the name

Whatever you choose, the phone extension you type must match the protocol. SIP, PJSIP, and IAX2 names should not contain dashes, while a Zap channel like 25-1 is entered with its full channel string. The Extension is the device name minus the protocol prefix, so SIP/test101 becomes test101 in the field. Get the protocol and the name out of step and the auto-created account will not match what the device expects, and registration fails.

If you ever find yourself unsure mid-form, back up to the one question that resolves almost every case: does a real device need to register here. If the answer is yes, you are choosing among SIP, PJSIP, and IAX2, and the device itself usually tells you which. If the answer is no, you are either describing analog hardware on a channelbank, which is Zap, or you are listing a number to dial out to, which is EXTERNAL. The menu looks like five equal options, but in day-to-day work two of them cover the overwhelming majority of phones, and the rest are there for specific jobs you will recognise when you meet them.

Once the protocol is right, the rest of the entry follows the same pattern: a dialplan number, a Server IP to pick the dialer, an agent login, and a Registration Password for the device. For the difference between the two SIP options, read what the PJSIP option means, and the phones pillar guide walks the entire form.

On a hosted dialer the protocol is preset and tuned, and a fresh server is registering phones in under 40 seconds. See VICIfast plans to find the tier that fits your team.