carriers-sip
SIP trunk
A virtual phone line over the internet that connects your dialer to a carrier, letting you place and receive many calls at once without physical wires.
A SIP trunk (Session Initiation Protocol trunk) is a virtual phone line that runs over the internet. Instead of copper wires running into your building, your dialer opens a connection to a Carrier and uses it to place and receive calls. One trunk can carry many calls at the same time, which is exactly what a call center needs. In VICIdial, a Trunk is the link between your server and the outside phone network.
Each active call on a trunk uses one Channel. The number of channels your trunk supports sets your ceiling for Concurrent calls — that is, how many conversations can run at once. If you buy a trunk rated for 50 channels and try to start a 51st call, it fails. Picking the right capacity is one of the first things to get right when you size a campaign.
How a trunk authenticates
Before a trunk can pass calls, the carrier needs to know it is really you. That happens either through IP authentication, where they recognize your server's public address, or through a login that uses a Registration string. Both are common, and your provider will tell you which they support. Once the trunk is authenticated, your SIP (Session Initiation Protocol) traffic flows freely in both directions.
Most VICIdial setups run one trunk for outbound dialing and sometimes a second for inbound traffic tied to a DID (direct inward dialing). You can also split work across trunks from different carriers for redundancy, so a hiccup on one provider does not take your whole floor offline. Keep an eye on how close you run to your channel limit, because a trunk that is constantly maxed out will start dropping calls during your busiest hours.
Related terms
Carrier
A carrier is the phone company that actually carries your calls onto the public phone network — VICIdial dials, the carrier delivers.
Channel
A single call path on your trunk, where each live call uses exactly one channel, so the channel count is the cap on how many calls can run at once.
Concurrent calls
The number of separate phone calls running at the same moment on your system, which sets the real ceiling on how busy your call center can get.
IP authentication
A way for your carrier to recognize your dialer by its public IP address instead of a username and password, so calls connect without login credentials.
SIP (Session Initiation Protocol)
The standard signaling protocol that sets up, manages, and ends internet phone calls — how VICIdial talks to phones and carriers.
Trunk
The connection between your VICIdial server and your phone carrier that actually carries calls in and out of the system.