SIP Trunk
Short answer: A SIP trunk is a SIP connection joining a phone system, typically a PBX, to a provider that bridges it to the public telephone network. It stands in for physical phone lines with an internet link, carrying calls both ways for the numbers assigned to it. A SMS Conecta number's SIP credentials can be loaded into a PBX as such a trunk.
The word trunk goes back to the bundled copper lines that once ran from office switchboards to the phone company. The SIP version performs the same role, just in software.
Definition
A SIP trunk is an account or connection on the provider side, verified by credentials or IP address, that allows a PBX to send outbound calls into the phone network and accept inbound calls for the numbers it's assigned.
How it works
Either the PBX registers to the provider's SIP server, or the provider pushes calls to the PBX's address directly. Inbound calls to a DID travel over the trunk, and the PBX decides whether they land on an extension, a queue or a menu. Outbound calls run the opposite way, with the PBX picking which number to show as caller ID.
How it applies to SMS Conecta
SMS Conecta issues SIP credentials for every number, authenticated with digest auth against sip.smsconecta.com. Inside Asterisk, FreePBX, 3CX, FusionPBX or VICIdial, each number gets added as a registration-based trunk. SMS Conecta handles the number and the trunk itself; anything like queues, call recording or predictive dialing comes from your own PBX or dialer software rather than from SMS Conecta.
Trunk versus single SIP account
| SIP trunk | SIP account in a softphone | |
|---|---|---|
| Connects | A PBX used by many people | A single app on a single device |
| Routing | The PBX decides the destination | Calls ring the app straight away |
| Typical user | Businesses and call centres | Individual users |
Related terms
- SIP
- PBX
- DID
- Caller ID
Frequently asked questions
Is a PBX required to use a SIP trunk?
Normally a trunk hangs off a PBX. If it's just you, registering the same credentials directly in a softphone is the simpler route.
Can a SMS Conecta number act as a FreePBX trunk?
Yes. Set it up as a registration trunk using the number's SIP username and password against the server sip.smsconecta.com.
Does the trunk support predictive dialing?
No. SMS Conecta hands you the number and SIP credentials; dialing modes themselves come from software like VICIdial.
How many outgoing minutes come with a number?
Each number carries 1,000 outgoing minutes per month plus 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)