How a SIP trunk works
SIP trunk connects a company PBX or cloud-based exchange with the provider via the internet. The provider assigns a telephone number or an entire block of numbers and ensures call routing from the public switched telephone network.
- Outgoing calls travel from the central office via the internet to the provider and then into the network.
- Incoming calls from the provider are routed by the central hub to the correct branch.
- The number of simultaneous calls depends on the agreed capacity, not on the number of physical lines.
Why companies are switching to SIP trunking
SIP trunk offers several practical advantages over ISDN or analogue lines:
- Lower operating costs - VoIP calls are generally cheaper than landline calls.
- Flexible capacity - The number of simultaneous calls can be adjusted without requiring a technician's physical intervention.
- Geographical independence - numbers with a local area code can be used even without a physical branch at that location
- Non-geographic and special numbers - easily add 800 numbers, DID extensions or numbers with different prefixes
What to watch out for when deploying SIP trunks
The quality of calls over a SIP trunk depends on the internet connection. For smooth operation, we recommend setting up QoS (Quality of Service, voice traffic prioritization) on the company router so that calls take precedence over other traffic.
Another common problem is SIP ALG (Application Layer Gateway) - a feature on some routers that modifies SIP packets and causes call drops or one-way audio. If calls do not work correctly, try disabling SIP ALG on the router.
On virtualni-ustredna.cz, adding SIP trunks is part of the standard setup, and the wizard will guide you through every step.
Frequently Asked Questions
How many concurrent calls does the SIP trunk support?
The number of simultaneous calls depends on the capacity agreed with the provider. Unlike physical lines, SIP trunk capacity can be quickly increased or decreased without physical intervention.
Can I have a SIP trunk from a provider other than the Cloud PBX?
Yes, SIP trunk and Cloud PBX are separate services. They can be combined from different providers if both support the standard SIP protocol.
Will I be able to keep my existing telephone number when switching to a SIP trunk?
Yes, the phone number can be ported from the current operator. The switch does not require changing the numbers that customers know.