Glossary · Hosting & DevOps
SIP Trunking
Overview
What SIP trunking is
SIP trunking is a way to connect a business phone system (a PBX) to the public switched telephone network (PSTN) over an internet connection instead of physical phone lines. SIP, the Session Initiation Protocol, is the standard used to set up, manage, and end voice and video calls.
A SIP trunk is effectively a virtual version of a traditional phone line: it carries voice as digital packets over IP and provides the channels a business needs to place and receive external calls.
How it works
An organization's PBX connects to a SIP trunk provider (an internet telephony service provider) over the internet. The provider bridges those SIP-based calls to the PSTN so the business can reach and be reached by ordinary phone numbers.
Each trunk supports a number of simultaneous calls (channels), and capacity can usually be scaled up or down without installing new physical lines. This is why SIP trunking is described as consolidating voice and data onto one network connection.
Why it matters
SIP trunking often reduces telephony costs and adds flexibility compared with legacy PRI or analog lines, because businesses pay for channels they need and can adjust capacity as demand changes. It also supports remote and distributed teams working from a single phone system.
SIP trunking and VoIP are related but distinct: VoIP describes carrying voice over IP in general, while SIP trunking specifically connects a phone system to the PSTN. Voice quality depends on adequate internet bandwidth, so provisioning and network quality matter.
Where we use it
Related Zen in Tech services
How our team puts SIP Trunking to work in real projects.
FAQ
SIP Trunking — common questions
What is the difference between SIP trunking and VoIP?
VoIP is the broad concept of carrying voice over the internet, while SIP trunking is a specific service that connects a business phone system to the public telephone network using the SIP protocol. SIP trunking is one way to deliver VoIP at scale.
What do you need for SIP trunking?
You typically need an IP-enabled PBX (or a cloud PBX), a reliable internet connection with enough bandwidth, and an account with a SIP trunk provider. The provider supplies the channels and connects your calls to the PSTN.
Does SIP trunking save money?
It often lowers costs versus traditional PRI or analog lines because you pay for the channels you use and can scale capacity without new physical wiring. Actual savings depend on call volume, provider rates, and your existing setup.
Need SIP Trunking done right?
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Knowledge hub
From our knowledge hub
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