Definition
A SIP trunk is a virtual connection that carries phone calls over IP between a business phone system or voice platform and a carrier, using the Session Initiation Protocol (SIP) for call setup and RTP for the audio.
SIP (defined in IETF RFC 3261) handles signalling: inviting a party to a call, ringing, answering and hanging up. The voice itself travels as RTP media streams. A trunk is the configured relationship between two SIP endpoints, usually authenticated by IP allowlisting or credentials, with a set number of concurrent call channels.
Trunks replace physical lines (such as ISDN PRI) and connect PBXs, contact-centre software and programmable voice platforms to the public telephone network. They make it easy to add capacity, route calls between countries and use local numbers.
Key parameters to agree with a carrier are codecs (for example G.711 or G.729), concurrent channel limits, caller ID (CLI) handling, number formats (E.164), DTMF transport, encryption (TLS for signalling, SRTP for media) and failover between trunks.
In the GCC, VoIP services and international call termination are regulated and licensed, so trunks to local numbers are normally provided by, or through agreements with, licensed operators. Confirm what is permitted in each country during onboarding.
OmniChannels.ai, through BroadNet's voice capability, lets businesses bring their own carrier via BYOC SIP trunks.
Example
INVITE sip:+97145551234@carrier.example.net SIP/2.0