carriers-sip
SIP (Session Initiation Protocol)
The standard signaling protocol that sets up, manages, and ends internet phone calls — how VICIdial talks to phones and carriers.
SIP, short for Session Initiation Protocol, is the standard that sets up and tears down internet phone calls. It handles the signaling — "ring this number," "the call is answered," "hang up now" — while the actual voice audio travels alongside it. It's the common language most modern phone systems, including VICIdial, speak.
VICIdial uses SIP in two directions. Agents' softphones use it to complete phone registration so the server knows where to send call audio. And the server uses it to reach your carrier over a trunk, which is how outbound calls actually leave your system and arrive on the public phone network.
Why it matters: when something "doesn't connect," the problem is usually in SIP signaling — a wrong password, a blocked port, or a firewall mangling the messages. Knowing that calls are SIP under the hood tells you where to look when audio is one-way, calls drop after a few seconds, or a phone won't register.
SIP isn't the only option — iax2 (Inter-Asterisk eXchange) is an older protocol that some setups still use between servers — but SIP is the default almost everywhere now, especially for a remote agent and for routing inbound calls that arrive on a did (Direct Inward Dialing number). If you're choosing a provider, see choosing a SIP carrier.
Related terms
Carrier
A carrier is the phone company that actually carries your calls onto the public phone network — VICIdial dials, the carrier delivers.
DID (direct inward dialing)
A DID (direct inward dialing) is a phone number you own that routes incoming calls straight into VICIdial, usually to a chosen inbound group.
IAX2
Inter-Asterisk eXchange version 2, a call-signaling protocol built for Asterisk that carries both signaling and audio over a single port.
Phone registration
The process where a softphone or SIP device announces itself to VICIdial so the server knows where to send the agent's calls.
Remote agent
An agent who logs into VICIdial from outside the office — usually from home — connecting their phone and screen over the internet.
Trunk
The connection between your VICIdial server and your phone carrier that actually carries calls in and out of the system.