GlossaryPhones
SIP trunk
A SIP trunk is a virtual phone line delivered over the internet that connects your own phone system (an on-site or hosted PBX) to the public telephone network, replacing traditional analog or digital carrier lines.
01 In depth
What it is, why it matters and what to ask a vendor
SIP, the Session Initiation Protocol defined in RFC 3261, sets up and ends calls between systems. A SIP trunk is a carrier service that uses it: your PBX sends outbound calls to the carrier over your internet connection, and inbound calls to your numbers arrive the same way. Capacity is sold as concurrent call channels rather than physical lines.
Growing businesses with a PBX they still like (Avaya, Yeastar and similar systems) use SIP trunks to cut line costs and add capacity without replacing the system. It is also a step toward the cloud: numbers move to a carrier that can later point them at a hosted platform or an AI voice agent.
Ask a carrier how many concurrent calls are included and how bursts are billed, whether the trunk is registration-based or IP-authenticated, how E911 is provisioned for each location, what failover happens when your internet is down, whether your PBX is certified with them, and who configures the firewall rules.
03 At Telxpress
Where this shows up at Telxpress
The pages and articles where this term does real work: what we advise, build and support.
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Business VoIP & Cloud Phone Systems in Irvine
VoIP, cloud phone systems, UCaaS and SIP trunks from Yealink, Nextiva, Avaya, Yeastar and Polycom, installed, supported and ready for AI call handling.
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Business Internet, Fiber, SD-WAN & Wi-Fi
Business internet, fiber, SD-WAN, Wi-Fi and carrier services for Orange County offices, selected and managed by one local partner with 24/7 support.
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Business Networking, Firewalls & Managed Wi-Fi
Switching, routing, Fortinet firewalls, Ubiquiti and Cisco Meraki Wi-Fi and managed network services for offices that depend on reliable connections.
04 Sources
Public references
The standard or law this definition rests on, as published by its owner. Fetched and checked on the review date above.