For many comms resellers SIP Trunks are synonymous with unreliability, poor voice quality and complicated and troublesome installation.   In many cases this perception is based on past experiences with low quality IP connectivity (eg. highly contended ADSL) or SIP providers whose infrastructure consists of little more than a server in their spare bedroom and a home broadband connection.

Many “early adopters” who have experienced this type of setup in the past have now been scared away from VoIP and are sticking to what they know – analogue lines and ISDN.  An understandable position to take, although now may be the time to re-think adding SIP Trunks to your offerings.  Things have moved on.  Reliability, interoperability and features have vastly improved and SIP is a viable ISDN alternative.  But still avoid the “spare bedroom” providers!

SIP relies entirely on the IP network between the SIP-PBX and the ITSP (Internet Telephony Service Provider).  An unsuitable or unreliable connection will cause problems for the signalling, causing calls to fail or drop mid-call, and voice quality will be variable.   SIP Trunks have suffered from the perception by many that you “just need an Internet connection” which is not the case.

You need a connection that will provide the amount of bandwidth that you require, is not heavily contended (ie. you are not sharing the bandwidth with your neighbours) and is backed up by an SLA that ensures faults are resolved promptly.  Most of the cheaper DSL products do not meet these criteria.

Thankfully the trend for connectivity over the last few years has been increased bandwidth and reliability with falling costs .  This means that connectivity such as Ethernet has become much more affordable for businesses and this lends itself well to SIP connectivity.

Many dealers who have experienced issues with SIP Trunks in the past have since realised that the ITSP they were dealing with were a lot smaller than their flashy website suggests.  This in itself is not an issue, but a robust SIP infrastructure costs a significant amount of money to build and many providers cut corners with an inevitable effect on reliability.  Many ITSPs are actually just reselling other providers services.  Again, not necessarily a major problem, but most comms dealers would prefer to be working directly with the people who own and manage the platform.

There are now several providers in the UK who can offer business class SIP trunking.  Thankfully the less professional providers seem to be either upping their game or getting out of the SIP Trunk arena.  This in turn should give comms dealers more confidence in the provider they choose.

It is often assumed that SIP Trunks offer less resilience and business continuity benefits than traditional circuits.  This can, in fact, be the reverse.

Imagine a customer with multiple branch offices.  Each site can work independently, but in the event of a site becoming out of action (power cut, fire, etc) the calls can be instantly delivered to alternative sites – seamlessly and without divert costs.

Even single-site customers can benefit from the resilience provided by SIP.  Calls can be diverted by the SIP provider to external numbers, or even queued or sent to a voicemail system.  Being able to achieve this within the provider network is a huge benefit when considering business continuity.

Obviously SIP and Unified Communications (ie. the convergence of voice and data applications) go hand in hand – but there are also several features that are inherently available to SIP trunks, some of which would be very expensive or unavailable when using traditional ISDN/analogue lines

Anyone who has had clients move from one BT Exchange area to another will be well aware of the issue of moving numbers and the need for number changes or costly diverts.  In the SIP world there are no longer geographic limitations – just port the numbers into the SIP platform and they can be delivered to the SIP-PBX anywhere in the country (or potentially, the world)

SIP Trunks offer scalability that is difficult or time-consuming to achieve using ISDN or analogue lines.  Most SIP providers charge on a per channel, per month basis.  So if a customer has a need for more call capacity (even if it is for a short duration – ie. for a marketing campaign or event) the capacity can be switched on immediately.  No waiting for an engineer to turn up to install, and no minimum term contracts.

To conclude, SIP Trunking has matured, and offers a feasible alternative to ISDN.  It can deliver significant business benefits with regard to resilience, features and cost.  However, care should still be taken when choosing your connectivity and SIP providers – they are not all the same!