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An SME’s guide to SIP Trunking

With the continuing spread of high-speed broadband throughout the UK, SIP trunking is witnessing uniform growth as SMEs embrace the idea of unified communications (UC) systems and VoIP. SIP trunking is not only more flexible and durable than traditional voice communications systems, but can also be a huge cost saver.

With all the benefits that SIP trunking offers however, it is important to be aware of the technical and logistical factors your business needs to take into consideration when looking to implement a new communications network. Every new system has unique components, and it is essential to evaluate how those elements could affect your organisation’s existing communications infrastructure.

Below we discuss some the issues to be aware of when considering SIP trunking as well as some of the specific benefits it offers.


Interoperability is hardly ever an issue nowadays, with most leading PBX brands able to support SIP. Those that aren’t can be easily converted using a ‘gateway’ rather than replacing the PBX (which is really expensive).


Older equipment may not be capable of handling an updated VoIP telephony system so when upgrading your telephone network to SIP trunking it makes sense to factor in the cost of upgrading your handsets and headsets so you can fully realise the benefits and increased functionality of such a system.

Reliance on Broadband

SIP trunking is entirely dependent on a reliable broadband connection. The addition of voice traffic to an existing connection can place a strain on your current network, leading to a decrease in bandwidth and a drop in call quality.

It’s highly recommended that you establish that your internet provider can handle the surge in data usage. If this can’t be done then you should consider implementing leased or assured lines to guarantee call quality.


Security risks with SIP Trunking can be easily safeguarded against using such secure SIP (which use Transport Layer Security), firewalls, border control, and fraud monitoring systems.

It’s of course always wise to make sure your security is watertight and up to date eliminate any risk of hijacking of call-signalling data, eavesdropping, tampering, or DoS attacks. With a robust SIP in place though this is highly unlikely to happen.


Financial savings are an integral benefit of SIP trunking. By centralising your PSTN with SIP trunking you negate costly Basic Rate Interfaces (BRIs) and Primary Rate Interfaces (PRIs) associated with ISDN systems.

Also, merging your data and voice into a single line not only reduces the resource costs required to efficiently operate your UC, but eliminates the monthly rental fees associated with ISDN. You will also be able to conduct free calls between other sites within your company and many providers provide free calls to mobiles as well.


With SIP trunking your business is able to quickly expand or consolidate, on a per channel basis and avoid the cost of unused lines, bringing about huge cost benefits and flexibility.

With the potential channels to be added instantaneously, your communication systems can be as fluid as your business’s fluctuating needs.

Flexibility and Redundancy

With SIP trunking, numbers are no longer tethered to a set location and can be easily transferred to a new location. Additionally, secondary paths allow for the re-routing of incoming calls, allowing your system to automatically divert calls to a different site if all the lines at your primary location are busy while simultaneously insuring continuation of service should a location suffer a network failure.

It is important that you have a clear plan for numbering before embracing SIP, including extensions, routing, promotional lines and hunt groups, so that configuration can be done quickly and accurately.

Use of ENUM

SIP trunking uses ENUM (Telephone Number Mapping) to automatically match outgoing calls with a known SIP address. It minimises the use of the PSTN and maximizes network calls for further costs savings. As VoIP systems become more commonplace, the low cost of using SIP will continue to drop.


SIP trunking offers both lower costs and greater flexibility over conventional communication systems. Not all providers are equally qualified in their abilities to troubleshoot issues and manage their quality of service so it’s important to properly assess the logistics and costs of implementing SIP trunking into your existing telephony architecture.

A reputable SIP provider will work with you throughout the process to implement a plan that responds directly to your company’s objectives in moving over to SIP.

Finding a good SIP trunking provider is not difficult if you know what to look for, but always be informed before making a final decision.

Gemma Maroney is Marketing Manager at Unified Communications Company Solution IP