SIP Trunks

A Guide to SIP Trunks

Traditional telephone (TDM) systems in business environments are usually set up on a separate or dedicated wiring infrastructure to a company’s data network and connect directly to the PSTN (Public Switched Telephone Network) via analogue or ISDN lines. This has resulted in companies having to invest in two entirely separate wiring systems, often from different vendors.

VOIP systems (Voice Over Internet Protocol) now mean that a company can share their LAN for both voice and data. Telephone extensions can now be connected to the same wiring network as their computers. Even the outgoing data connection can be used for carrying calls, reducing or eliminating the need to invest in separate analogue or ISDN lines which have traditionally been used for their voice traffic.

Internet Telephony Service Providers (ITSP) are able to supply voice channels over a company’s internet data connection using SIP (Session Initiation Protocol) to carry voice calls which traditionally would have been made over analogue or ISDN lines. The ITSP will then use their interface with the PSTN to connect calls to their destination.

What are the benefits of using SIP trunks?

The most common benefit, and perhaps the most important of which includes a reduction in on-going phone costs. SIP trunks are provided at lower rental charges than other standard analogue or digital telephone lines. SIP trunk calls are nearly always cheaper than ISDN calls, even with reputable least cost routing in place, plus your SIP supplier can provide the added benefit of routing VOIP to VOIP calls off the traditional PSTN or mobile network providing telephone call savings, particularly if businesses operate across different sites or employ remote workers as these calls are often provided free.

Additional Benefits of SIP

  • A single, converged voice and data network costs less than separate network connections. Modern business is increasing its use of data services like email, the internet and online applications. Using SIP means your data connection can be used for voice too.
  • SIP to SIP calls on the same ITSP network are free. Multi-site organisations can make substantial call savings between their sites by using SIP lines.
  • With SIP trunking you only pay for the capacity you require, it is easier and quicker to increase or decrease channels with a SIP service.
  • SIP trunking also has the benefit of being able to operate without geographic telephone number constraints; area telephone number codes can be routed to any location where a data connection is available. Companies moving out of exchange area are able to ‘port’ their number to SIP and retain it wherever they move to. Companies can also use this service to convey a local presence within a location despite not having offices in that area.
  • Less hardware costs – traditionally, additional ISDN channels have meant the need for additional cards for the telephone system. As well as the cost of the extra card there can be associated license fees, installation costs and annual maintenance charges. SIP trunks do not require any further hardware.
  • Disaster recovery – although a robust business grade internet service should be every bit as reliable as traditional telephone lines, SIP providers have the ability to route calls over alternative paths such as landlines or mobile phones in the case of inbound call failure, a fast, seamless transfer will ensure business continuity.

Take a look at our guide to VoIP systems and how we can help install and configure a business VoIP system on your network, provide the necessary phones and other additional equipment in order to set-up your business VoIP system.

The Next Step…

For more information on SIP trunks and how they go hand in hand with a VoIP phone system please contact us on 01392 824 022 or email

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