What the PJSIP protocol option means for a phone

Open the Client Protocol menu on a VICIdial phone and you will see SIP, PJSIP, IAX2, Zap, and EXTERNAL. The PJSIP option tends to raise eyebrows because it looks so close to plain SIP. It is in fact a newer engine for the same job, and Asterisk ships it as the modern way to handle calls. Knowing what it changes, and what it does not, keeps you from second-guessing the menu every time you add a handset.

PJSIP is a newer SIP stack

Both PJSIP and the classic protocol speak SIP (Session Initiation Protocol) on the wire. The difference is the code inside Asterisk that drives the conversation. The original channel driver was simple and battle-tested, while PJSIP is the rewrite that newer Asterisk versions favour. From the phone's point of view it is still registering, ringing, and carrying audio the same way. From the server's point of view, PJSIP gives finer control over things like multiple devices on one account.

Because it is still SIP underneath, a desk phone or Softphone configured for SIP can usually talk to a PJSIP account without any change on the device.

It helps to think of the two stacks as two engines bolted into the same car. The steering wheel and pedals, meaning the registration, the ringing, and the audio, feel the same from the driver's seat. Under the hood, the older driver has been around long enough that almost any quirk you might hit is well understood, while the newer one was written to handle modern setups more cleanly and is where ongoing development is focused. Neither is a phone protocol in its own right. Both are just the part of the server that speaks SIP, which is why the choice rarely changes anything the agent ever sees.

Filling in the phone entry

PJSIP entries follow the same naming rule as SIP and IAX2: the phone extension field should not contain any dashes. You still set a dialplan number, a Server IP, an agent login, and a Registration Password, and the matching account is generated on the chosen server shortly after you save. The Extension you type is the device name Asterisk will know, minus the protocol prefix.

Where PJSIP sits among the choices

flowchart TD
  A[Client Protocol menu] --> B[SIP classic stack]
  A --> C[PJSIP modern stack]
  A --> D[IAX2 single port]
  A --> E[Zap channelbank]
  A --> F[EXTERNAL dialplan only]
  B --> G[Account auto-built]
  C --> G
  D --> G

When to pick PJSIP

If your platform was built around the newer stack, PJSIP is the natural choice and your phones will register against it cleanly. If you inherited a system that has always used the classic SIP driver, there is rarely a reason to switch a working phone over. Both create their account automatically, both carry the same RTP audio, and both honour the Registration Password you set. The thing to avoid is mismatching the device and the entry, but since a SIP softphone talks happily to a PJSIP account, that mismatch is forgiving in practice.

• PJSIP is the modern SIP engine in Asterisk, not a different phone protocol.
• No dashes in the phone extension, same as SIP and IAX2.
• Most SIP devices register to a PJSIP account with no changes.

For the difference between the two everyday options, read SIP vs IAX2 phones, and the phones pillar guide ties all the fields together.

On a hosted dialer the protocol stack is already chosen and tuned for you, so a new server is registering phones in under 40 seconds. See VICIfast pricing to see which plan fits your seat count.