SIP Trunk
Short answer: A SIP trunk is a SIP connection between a phone system, usually a PBX, and a provider that links it to the public telephone network. It replaces physical phone lines with an internet connection, carrying calls to and from the numbers assigned to it. A ZuteSIP number's credentials can be added to a PBX as a trunk.
The word trunk comes from the bundles of copper lines that once connected office switchboards to the phone company. The SIP version does the same job in software.
Definition
A SIP trunk is a provider-side account or connection, authenticated by credentials or IP address, that lets a PBX place outbound calls to the phone network and receive inbound calls for its numbers.
How it works
The PBX registers to the provider's SIP server, or the provider sends calls to the PBX's address. Inbound calls to a DID arrive over the trunk and the PBX routes them to an extension, queue or menu. Outbound calls go the other way, with the PBX choosing which number to present as caller ID.
How it applies to ZuteSIP
ZuteSIP provides SIP credentials per number, using digest authentication against sip.zutesipdialer.com. In Asterisk, FreePBX, 3CX, FusionPBX or VICIdial you add each number as a registration-based trunk. ZuteSIP supplies the number and trunk; features such as queues, recording or predictive dialing come from your PBX or dialer software, not from ZuteSIP.
Trunk versus single SIP account
| SIP trunk | SIP account in a softphone | |
|---|---|---|
| Connects | A PBX serving many users | One app on one device |
| Routing | PBX decides where calls go | Calls ring the app directly |
| Typical user | Businesses, call centres | Individuals |
Related terms
- SIP
- PBX
- DID
- Caller ID
Frequently asked questions
Do I need a PBX to use a SIP trunk?
A trunk is normally connected to a PBX. For a single user, registering the same credentials in a softphone is simpler.
Can I use a ZuteSIP number as a trunk in FreePBX?
Yes. Add it as a registration trunk with the number's SIP username and password and the server sip.zutesipdialer.com.
Does ZuteSIP offer predictive dialing on the trunk?
No. ZuteSIP supplies numbers and SIP credentials; dialing modes come from software such as VICIdial.
How many minutes does a number include?
Each number includes 1,000 outgoing minutes per month and unlimited incoming calls.
Related pages
- SIP
- PBX
- DID
- FreePBX setup
- Asterisk setup
- 3CX setup
- SIP dialer vs softphone vs predictive dialer
- SMS Verification
Sources
- IETF: RFC 3261, SIP: Session Initiation Protocol (as of September 2026)