Glossary
What is SIP trunking?
Definition
SIP trunking is a method of delivering phone service over the internet using the Session Initiation Protocol. It provides virtual phone lines, or trunks, that connect a business phone system to the public telephone network. SIP trunks replace traditional physical phone lines with internet-based connections.
01How SIP trunking works
SIP is a signaling protocol that establishes, manages, and ends voice sessions over IP networks. A SIP trunk carries these sessions between a business phone system and a provider that connects to the wider telephone network. Each trunk can handle multiple simultaneous calls, with capacity provisioned as channels.
02SIP trunking for businesses
By replacing physical lines with SIP trunks, businesses can scale call capacity up or down without installing new hardware. Trunks connect on-premises PBX systems or cloud platforms to the phone network and often support multiple locations under one setup. This flexibility makes it a common foundation for modern and AI-enabled phone systems.
03SIP trunking versus VoIP
VoIP is the broad category of carrying voice over IP, while SIP trunking is a specific way to provide the connection between a phone system and the telephone network. SIP handles the call setup and signaling, and VoIP media protocols carry the audio. In practice SIP trunking is one of the main technologies that makes business VoIP possible.
Frequently asked questions
How is SIP trunking different from VoIP?
VoIP is the general technology for calling over the internet, while SIP trunking is a specific service that connects a phone system to the public telephone network using the SIP protocol.
What is a SIP channel?
A channel is capacity for one concurrent call on a SIP trunk. A business provisions enough channels to cover the number of simultaneous calls it expects.
Related terms
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