Glossary
SIP trunk
A SIP trunk does the job the phone company's copper lines used to do: it carries calls between your PBX and the outside world. The difference is that it runs over your internet connection and its capacity is a setting, not wiring.
A SIP trunk is a virtual phone line delivered over the internet that connects a business's own PBX to the public telephone network. It replaces physical lines such as analogue lines or PRI circuits. Inbound calls to the business's numbers arrive over the trunk, and outbound calls leave the same way. Capacity is measured in simultaneous calls and can be changed without new wiring, which is the main practical advantage.
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What it means
A business with an on-premises or self-hosted PBX still needs a connection to the outside telephone network. Historically that was a bundle of analogue lines or a digital PRI circuit rented from the phone company. A SIP trunk provides the same connection as data, over the internet, using the SIP protocol. The PBX registers to the provider, or the provider is configured to send calls to the PBX's address, and calls flow in both directions.
Because the trunk is virtual, its size is a number of concurrent channels rather than a count of physical lines. Adding capacity for a busy season, or reducing it afterwards, is a configuration change. Numbers, including ported numbers, are assigned to the trunk and delivered to the PBX with the dialled number so the PBX can route them.
How it is used in a business phone system
- A company keeps its existing IP PBX and replaces its PRI with a SIP trunk sized for its peak simultaneous calls.
- Local and toll-free numbers are pointed at the trunk; the PBX receives each call with the dialled number and applies its own routing.
- Outbound caller ID is set per number so each department or location shows the right number.
- A second trunk or a forwarding rule provides a fallback if the PBX or the site's internet connection is unavailable.
How 3CTel uses it
3CTel provides SIP trunking for customers who keep their own PBX. A specialist confirms the PBX model and its SIP settings, sizes the trunk for concurrent calls, assigns or ports the numbers, and tests inbound and outbound calls on a temporary number before the existing numbers are moved. The registered service address for 9-1-1 is confirmed for each site during setup. Pricing is quoted for the channels and numbers required.
SIP Trunking
Carrier-grade SIP trunks for the PBX you already run — channels, DIDs and failover sized to your traffic.
Learn more: SIP TrunkingSIP trunking
Canadian numbers and call paths for the PBX you already run.
Learn more: SIP trunkingNumber porting
How a port works, what you need to provide, what causes delays, and what 3CTel does at each step.
Learn more: Number portingCommon questions about SIP trunks
How many channels does a SIP trunk need?
As many as the maximum number of calls the business expects to have in progress at the same time, inbound and outbound combined. A useful starting point is the number of lines or PRI channels currently in use, adjusted for how often they are all busy. Because channel counts can be changed later, it is reasonable to start near current usage and adjust.
Will my existing PBX work with a SIP trunk?
Most IP PBX systems from the last decade support SIP trunking directly. Older systems with only analogue or digital line ports need a gateway that converts between the trunk and the PBX. The specific model and firmware are checked during planning, and the trunk is tested against the actual PBX before any numbers are moved.
Related pages.
SIP Trunking
Carrier-grade SIP trunks for the PBX you already run — channels, DIDs and failover sized to your traffic.
Learn more: SIP TrunkingBusiness Phone Numbers
Local, toll-free and campaign numbers that all land in one system.
Learn more: Business Phone NumbersCloud PBX vs traditional PBX
Own the switch or rent it: ownership, maintenance, remote users and the path between them.
Learn more: Cloud PBX vs traditional PBXKeep your PBX. Replace the lines.
Tell us the PBX model, the number of concurrent calls you need and the numbers to move. A specialist will size the trunk, test it against your system and quote it.