The truth about SIP trunking

If you have ever wanted someone to explain what SIP trunking is and how it works, but been too afraid to ask, you’re not the only one. 

If you’ve ever been in a meeting where the term SIP trunking is being used, and you are sitting there thinking that you are the only person in the room who doesn’t know what it means, stop worrying. You will certainly not be the only one. SIP trunking is a term that few people really understand properly – and most of those who have some idea, probably don’t have any idea of how it works.

SIP stands for Session Initiation Protocol, and it’s essentially a set of rules that govern the way that voice calls over the Internet i.e. VoIP calls, are initiated, routed and ended. Put another way, SIP is the glue that holds VoIP services together.

Virtual alternative

SIP trunking is a way of creating a virtual trunk line – an end-to-end connection – over the Internet. On traditional analogue systems, this was done with circuit boxes and switches in local exchanges. The SIP trunk just re-creates that set-up, but without any of the hardware and physical elements.

In simple terms, SIP trunking is a way of simulating the way traditional business phone systems operate, using the Internet. Significantly, this also allows you to bring several channels together into a single connection, which massively reduces cost.

While most organisations would connect only VoIP systems to a SIP trunk, it is also possible to connect traditional analogue phone systems using a VoIP gateway. Either way, it allows you to go reduce the number of connections or lines required to support telephony.

This is very attractive for organisations with multiple locations, and especially those with an international or global presence, as it enables them to set up specific virtual connections to carry voice right across the organisation, routing all their VoIP services via the SIP trunk. The savings can be enormous – as much as 50% or more on line rentals and call charges alone and more if you factor in the reduced management and maintenance costs.

Extended flexibility

Add to this the extended flexibility in terms of scaling and numbering and improved resilience that SIP trunking offers, and it becomes even more appealing. And SIP can also carry instant messages, video conferences, emergency calls and other communications services, so it’s tremendously flexible.

As it is entirely virtual, it can also be scaled up and down very easily – unlike traditional trunk or ISDN lines, where you would have to purchase or rent the lines for a fixed period whether you were using them or not. It is also more reliable, because SIP trunking providers can re-route services to an alternative line if necessary. Old numbers can be transferred to the SIP trunk and it’s possible to set up and manage unlimited non-geographic and geographic numbers.

In truth is that, from a technical perspective, SIP trunking is complicated. But so are many technologies. You do not need to understand exactly how it works beyond the point that it provides as a virtual, more flexible and much more cost-efficient way of providing telephone lines. The benefits are what really matter – and that’s definitely worth remembering.


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