SIP trunk
A SIP trunk is a virtual connection that carries phone calls between a phone system and a carrier over the internet using the SIP protocol, replacing physical phone lines.
How a SIP trunk works
SIP (Session Initiation Protocol) is the standard used to set up and end voice calls over IP networks (VoIP). A SIP trunk links a phone system to a carrier. Incoming calls to the carrier's DID numbers arrive at the phone system through the trunk, and outgoing calls leave through it to the public phone network. Capacity is set in software rather than by the number of physical lines.
Why businesses use SIP trunks
- To connect a phone system to a carrier without physical lines.
- To choose a carrier by price or country coverage.
- To combine numbers from several carriers in one phone system.
SIP trunks in phone.systems™
phone.systems™ uses trunks in two ways:
- DIDWW numbers are assigned to the phone.systems™ trunk in your DIDWW account. This is part of the standard setup.
- Your own carrier (BYOC): in the Trunks area you add inbound trunks, each with its own SIP domain, and termination gateways and routes for outbound calls. Routes use longest-prefix matching — the most specific matching number prefix wins — and caller ID rewrite rules.
Separately, each phone.systems™ seat includes a SIP account, so users can connect a SIP IP phone or third-party softphone. SIP accounts support the codecs OPUS, G722, PCMU, PCMA, G729 and GSM, the transports UDP, TCP, TLS and WSS, and SRTP call encryption. See BYOC in phone.systems™.