What is a SIP Trunk?


What is a SIP Trunk?  SIP, short for Session Initiation Protocol, is the digital method of making and receiving phone calls over an internet connection. The term trunk in SIP trunking refers to virtual phone lines that you can use to make phone calls over the internet to anyone with a phone number. SIP trunks are replacing analogue and ISDN phone lines in the UK.


What are the benefits of SIP trunking?

SIP Trunking suits all kinds of businesses from the sole trader to multinationals. The amount of SIP Channels that a business requires can be worked out on simple 3:1 ratio, 3 members of staff to 1 channels of SIP Trunk. A business with 30 members of staff would generally have 10 active channels on the SIP Trunk.

The flexibility to make changes to the active channel count is a massive benefit to SIP, for example a business has a new sales campaign, this relies on a telesales team making multiple calls during a one-week period. The channel count can be upgraded on a live system meaning the channel quantity is instantly upgraded to allow normal business operational needs and covering the new need for more outbound telephone lines. When the campaign is over the channel count can be decreased back to the original count.

Cost Savings

There’s also the cost aspect of SIP trunks. Generally, SIP Trunks are a lot cheaper than fixed analogue and ISDN telephone lines and can also include bundles minutes and free of charge calls or a pay as you use tariff.


SIP trunks can be more reliable than traditional analogue circuits. Firstly, it is possible to support number failover, so if the primary number cannot be reached it can failover to a secondary number, potentially at a different location. Secondly, SIP trunks, when routing calls, do not have a fixed route end-to-end like traditional phone lines. SIP calls can take diverse routes to reach their destination, thereby overcoming network issues or outages that would have prevented analogue calls from connecting.

Call Quality

SIP trunks are designed to ensure that your digital phone connections have ample bandwidth to make high-quality calls. As long as your Telephone System isn’t overloaded, you can expect clear calls even during busy periods. With advances in artificial intelligence, we now have technology that automatically improves call quality and fixes errors like echoes and static. You shouldn’t have to worry about call dropouts or echoing connections.

Security & Fraud Management

Unlike older phone systems, your SIP trunks are dedicated connections for your calls. SIP providers monitor calls for unusual behaviour as part of the service, meaning anything unexpected will be flagged immediately.

Connectivity Photo


SIP trunks are not tied to a local exchange, it’s now possible to have local numbers in any region regardless of your physical location. Also, if you move premises, you can take the numbers with you wherever you move to.

Internet Connection

Your business will need a stable internet connection to run a SIP Trunk. That could be a standard FTTC SoGEA/FTTP service, or an Ethernet based Leased Line. QOS (quality of service) can be added to the Internet service which will provide priority to the voice data packets used by the SIP Trunk to be elevated above the data packets ensuring you always receive the best quality phone calls you need.

Contact Us

If you are interested in making the switch from the analogue or ISDN service that you currently have in place, get in touch via our contact us page.

We will ensure that your transformation to all digital phone lines is seamless and carefree.