The what, why, where, who and how of SIP trunking.

Very few industries have as many acronyms as the world of telephony. It is a constant source of both pride and embarrassment that I can converse with colleagues and industry people in these acronyms. One of the few industries that does rival telecoms for acronyms is the world of Information Technology or more commonly referred to as, you guessed it, IT. So when the two worlds collide, as they do with SIP trunks, then you can imagine how it could go from here. Let me make it simple, because a SIP trunk should not be WTF . . . IMHO!


What is it and what do you do with it?

What do you do with a SIP trunk? Well, you connect it to a telephone system, a.k.a. a PBX (don't laugh), to make and receive external calls. So assuming you have a PBX and your interested in adding a SIP trunk to it, lets move on. We will quickly divide and conquer the term before moving onto real examples.

SIP: First lets very briefly cover off what SIP actually is. Most people loosely translate SIP as just voice over IP or VoIP, and for the purposes of this article, they are loosely correct, so lets move on. Officially, SIP is an acronym for Session Initiation Protocol, which does not really help make it clearer at all. Explained another way, SIP is a communication protocol that guides the different IP voice and video streams to talk to each other, and even helps them decide the format of how they are going to talk to each other. I like to think of it as like the talking stick that gets passed around in a group therapy session. But much like the talking stick, SIP controls who speaks and when, but not the content or delivery of what is actually said. This is handled by other protocols which we won't cover here but also have some wonderful acronyms, including UDP, TCP, SDP and RTP.

Trunk: According to Wikipedia "trunking is a method for a system to provide network access to many clients by sharing a set of lines ... instead of providing them individually". So I can translate this as your clients being your telephone system extensions, sharing a set of lines. After all you don't need an external line for each extension unless you are operating a call centre environment. For an average office, the ratio we work to in the industry is 3:1, so a 30 extension PBX would have 10 external lines. These lines get referred to "channels" in the world of SIP trunking. So a 30 extension PBX would have a single SIP trunk with 10 channels.

Why bother?

SIP trunking is very flexible and allows you to move your PBX into the cloud, and around the cloud, as needed. Not only that but compared to the alternatives it is incredibly more cost effective, flexible, scalable, resilient and robust. But what are the alternatives? They go under different names in different countries, but you may know them as analogue lines, ISDN lines, basic rate or primary rate trunks. These are traditionally very expensive and inflexible when compared to SIP trunks, plus they can only be installed on-premise, so no cloud or hosted telephony options are available. They are often based on older copper technology, and often result in your PBX needing extra or additional resources to work. SIP trunks on the other hand, also offer extra services, which include increased automation for failover and even call tracking options.

The one catch with SIP trunks? You need a good internet connection wherever your PBX is located.

You can translate good here as being a speed of at least 100 kbps per channel or call. This means, using our previous example of 10 channels, we need a stable bandwidth connection of at least 1mbps dedicated for our SIP trunks to use. This is becoming an increasingly easy and cost effective amount of bandwidth to obtain, depending on where you are in the world. Hence the rise in the popularity of SIP trunks.

Where can you get SIP trunks?

I'm happy to say that SIP trunks are increasingly available in many countries across the world, . With even highly regulated countries, such as China, providing options now for consumers. That being said, the options and pricing available in different countries varies greatly. So it is wise to choose your partner carefully and always take a slow and gradual programme introduction in your approach. Speak with your current line provider, or PBX maintainer, to see what they can offer first.

If we are working with a new provider for a client, then we like to run a particular department or business function through a SIP trunk first for a few weeks or months, to make sure that the infrastructure, quality and set-up is correct. It also allows us to gauge call quality and expectation from the users, which can make or break any adoption plans. Choose your guinea pigs wisely as well, there is no point choosing people who don't use the phone much, as you won't get quality feedback.

Who would we recommend?

As I mentioned previously, I would always choose your provider wisely, however I can recommend one provider on a worldwide basis and that is a company called Twilio. Nearly all of our solution designs factor in a Twilio trunk, either as a backup/secondary provider, or indeed as the primary provider. They do not charge for their SIP trunks and they are 'elastic' in design, which means they have no channel limitations, so you can have as many calls running through them as your company or PBX can handle. They charge a reasonable price per minute and can access local numbers in over 50 countries, however you can only move your existing numbers to them if you live in the US or Canada. It is this reason that means they are only a secondary provider in some of our solutions.

How do we start?

One of my favourite aspects of Twilio is how quick and easy it is to get started. The signup process takes a few minutes, and depending on your skills and experience, it doesn't take many more minutes to have a SIP trunk configured on your PBX, as they have very good documentation and support. We have even developed a free online lecture that shows you how to create and connect a Twilio SIP trunk into our favourite PBX, which is called 3CX.

And before you roll your eyes at me for sliding in a final acronym, 3CX isn't an acronym for a change, it is the actual name of the product! And it is a great product. In fact when combined with Twilio, 3CX is about as robust and feature rich a PBX as you can get for the SME market in my opinion.