What is SIP trunking?

Posted on: 2015-12-18 | Categories: SIP

SIP trunking is a way of routing telephone calls and other types of business communications such as video and web conferencing over the Internet rather than using traditional telephone lines or ISDN.

SIP stands for Session Internet Protocol – a communications protocol for signalling and controlling multimedia communication sessions. SIP is widely used across the Internet for applications such as voice and video calls and instant messaging.

SIP trunking offers business a way to deliver unified communications that are reliable, robust, agile and feature rich while also achieving significant cost savings.

How SIP trunking works

In traditional landline telephony, the phone calls are routed from the business to the Public Switched Telephone Network (PSTN) using a dedicated line or a bundle of circuits.

SIP trunking routes the calls over the data network. The physical wires are no longer needed. All you need is your data bandwidth. Of course, by routing the calls over the Internet, SIP trunking helps to deliver a convergence of voice and data. This makes for richer communications. It removes the need for dedicated telecoms equipment, freeing up space and using less power. It can deliver more flexible costs and lower pricing. And it delivers greater reliability and imprfooved business continuity planning.

I think I get it… run that by me again

To understand SIP trunking, its help to clarify what some of the technology in a telecoms network is and what it does. Let’s start with the PBX.

Back in the early days of telephony, all calls were routed manually by a switchboard operator (nearly always a woman). As you will know if you’ve ever watched old black and white movies, calls were placed by picking up the phone and yelling “operator, get me the police.”

The operator would then physically connect two telephone lines together (jack to socket), or they would connect one telephone line to an outside line – the public switched telephone network or PSTN.

In time, these operators had their jobs replaced by robots in the shape of automatic exchanges. Within a business, the task of routing all the calls was handled by the PBX, or Private Branch Exchange. The PBX routed internal calls around the business or sent them off into the big wide world of global telecommunications by connecting them to the PSTN.

When the concept of sending voice calls over the Internet came along in the shape of Voice over Internet Protocol (VoIP), a switchboard or exchange was still needed to send the call to the right destination. This led many businesses to introduce the IP-PBX. This eliminated much of the old telephone cabling in the building and provided rich features such as call waiting and caller ID. It could also take voicemail messages and enable conference calls.

Now, whether it’s a woman in a black and white movie or a fancy IP-PBX, when the switchboard sends the call to the PSTN, it does so using trunking. A trunk line is a circuit connecting telephone switchboards, as distinguished from a local loop circuit. One trunk can carry lots of calls, which are then split up and spread out by the PBX.

(It’s called a trunk because it can carry lots of stuff over a long distance, in the same way that a trunk road carries lots of traffic between major cities.)

With traditional telecoms, the trunk was known as the Primary Rate Interface (PRI). This refers to a telecommunications interface standard used on an Integrated Services Digital Network (ISDN). It can carry multiple voice and data transmissions between the network and the PBX in your building.

A SIP trunk bypasses the PRI. It uses the data network to connect trunk calls from the switchboard (an IP-PBX) to the outside world (the PSTN).

So, a SIP trunk frees you from the requirement to route your communications along the physical network owned and operated by the traditional phone company. Instead it routes calls using your data bandwidth.

SIP trunking and VoIP – what’s the difference? Which is best?

We’ll look in depth at the relationship between SIP trunking and VoIP in a future blog post.

It is wrong to think of one as better than the other. They both deliver lower cost calls and unified communications, using largely similar technologies.

The bottom line is that one way or another, you need a PBX (private branch exchange) to route and manage your calls.. VoIP provides a PBX in the cloud with no setup, maintenance or up-front costs. It’s the right choice for smaller businesses, especially if you don’t already have a PBX. (They’re expensive, and tricky to set up).

Larger businesses, with hundreds of employees, are likely to save money with SIP trunking compared to VoIP, especially if they have already made the up-front investment in an IP-PBX. This is because with VoIP, you effectively need one channel per employee. With SIP trunking, you’ll get by with fewer channels.

So, if you have your own IP-PBX, it makes sense to go with SIP trunking. If you don’t have your own PBX, and don’t want the expense of implementing one, then go with a specialist VoIP provider. {{link to VoIPstudio website}} This will effectively give you your own PBX – but in the cloud.

It is also possible to have both SIP trunking and VoIP under one account. This way, you could have SIP trunking for the major premises and VoIP in smaller officers, regional and international offices or for home workers. This kind of hybrid account is rare – and at this stage we believe available only through GoTrunk and our partner VoIPstudio.

Advantages of SIP trunking – more for less
SIP trunking offers a huge range of benefits for business. We’ll look at them in depth in future blog posts, but for now they can be summarised as better communications for less money. SIP trunking offers:

Lower call costs – with free calls across the Internet, lower cost calls to mobiles and fixed lines and overall low-cost pricing.
Lower network costs – with no need for a dedicated phone network. With a PRI trunk, you have to buy lines in groups of 23. But with SIP channels, you can buy exactly the number you need and add more at any time. Or remove them just as easily.
Greater number flexibility – you can easily port your numbers if you change providers or move premises, or even move to an entirely new country or continent.
Ease of providing local numbers – with SIP trunking it’s easy to provide local numbers for customers wherever they are in the world. This opens up new business opportunities and makes a good impression.
High call quality – VoIP’s reputation suffered from poor call quality in the early days. That’s no longer the case if you have the right VoIP provider, but SIP trunking can deliver exceptional call quality. You can also ensure that phone calls take priority over other data so the calls always get through.
Increased reliability – SIP trunking makes it far easier to plan for business continuity in case of an emergency. If you had to vacate your building at short notice, for example, you could easily redirect all your calls simply by going into the web portal of your provider. You’ll still need bandwidth and Internet access, but you can be up and running again much faster than with traditional phone lines.

There are many more benefits to SIP trunking, some of them of interest to business leaders, others that will be most appreciated by engineers and technical staff. We’ll deal with them all in forthcoming blog posts. For now, if you’re still not sure what SIP trunking is (or how to explain it to the CEO!) then get in touch and talk to one of our consultants.

Despite all the complications around the technology, we can get you up and running and using SIP trunking in next to no time. In fact, there’s no better way to learn about SIP trunking than by diving in and getting started. You’ll be surprised how easy it can be. To take a free 30-day trial, register here.