Guide to SIP trunking

Guide to SIP trunking

How replacing your phone lines with BT SIP Trunk can benefit your business.

SIP trunking is a type of technology that lets you make calls over a data connection. Of course, there’s a lot of clever technology behind it but we’re not going into the technical detail here (SIP stands for Session Initiation Protocol, by the way). Instead, we’ll give you a layman’s overview of SIP trunking and the benefits it can bring to your business.


How does it work?

Many businesses use a phone line, an internet connection, and a phone system.

With SIP trunking you just need an internet connection and a phone system. No phone line. Calls are translated into data ‘packets’ and sent over your data network. Importantly, you’re able to continue using your existing phone system and handsets, so there shouldn’t be any noticeable disruption.


SIP trunking vs. traditional phone lines: which is right for my business?

One of the main benefits is cost saving. With SIP trunking you no longer need separate phone lines and calls are often cheaper than traditional calls. But there’s more to it than just cost.

Thinking of it as an IP (Internet Protocol)-equivalent of ISDN, let’s compare the two over five areas:

1. Upscaling

SIP trunking
The number of SIP trunks is determined by the bandwidth of the data network. Scaling up can be done easily as a configuration change. As the new trunks are virtual, you don’t need any new hardware for the phone system.

Each ISDN line has a limit on the maximum amount of voice channels: 2 channels for ISDN2; 30 for ISDN30. Scaling up can be costly and time consuming. You may need a new line if the maximum channels are already in use. You may also need new hardware for the phone system.

2. Back-up and continuity

SIP trunking
Calls can be directed to back up sites (or mobiles) in the event of the data network failing.

Back-up circuits are physical and can be expensive. Call routing can be expensive.

3. Cost        

SIP trunking
SIP trunks are generally cheaper, but there may need to be investment in the data network or phone system.

ISDN channels can be expensive to increase capacity and traditional phone systems can be costly to maintain.

4. Quality of service      

SIP trunking
Quality has improved significantly and many providers guarantee voice quality. 

ISDN is very reliable and has a high level of quality of service.

5. Productivity     

SIP trunking
SIP trunking can include productivity features (such as call management and online portals) and unified communications integration (like call recording and CRM).

Productivity and unified communications is limited, and often only enabled by the phone system rather than the ISDN.

Our customers often choose SIP trunking if:

  • They’re upgrading their phone system and/or internet connection and want to realise cost savings
  • They want an element of backup and resiliency
  • They want enhanced productivity features and integration with other services
  • They want to be able to quickly and easily upscale their voice channels


How BT can help: BT SIP Trunk

BT SIP Trunk is our SIP trunking proposition.

BT SIP Trunks are cheaper than traditional phone lines, come with a generous call allowance, and have free calls between BT SIP Trunks. The pricing structure is really simple, and there’s no spend commitment.

It works with BTnet, our market-leading leased line. BTnet is a dedicated internet connection that you don’t share with anyone else. Because this means less traffic on your line, you get faster speeds and more reliable internet connectivity. In fact, with BTnet you’ll get a 100% target availability SLA. When you’re using your internet connection to carry your voice traffic, it’s important that your internet connection is fast and reliable.

And because we own SIP trunking and the network, we can provide Quality of Service so you can be reassured that call quality will never be compromised. Quality of Service ensures calls are prioritised over other data traffic. In fact, your voice calls will have a dedicated bandwidth, so no matter how much other data you're consuming, your calls will never suffer.

You can have more flexibility with your phone numbers. With BT SIP Trunk phone numbers are no longer tied to the local exchange. So you can have any number on the service, allowing you to market yourself locally across the country. And if you need to move premises, you can take your numbers with you, wherever you go.

You’ll also have more business continuity options. Calls can be redirected to another BT SIP Trunk number and can automatically re-route to any other backup or resilient BTnet you have. This can be a much cheaper disaster recovery option than having a separate, dedicated voice back-up.

BT SIP Trunk has been designed for business use and extensively tested to work seamlessly with BTnet and BT phone systems. We install it as a complete solution; we’ll work with your IT team to ensure a smooth implementation. And once it’s up and running, we’ll give you a dedicated helpdesk who’ll provide support for all aspects of your new solution.


Who is BT SIP Trunk suitable for?

You need to have, or be considering installing, a BTnet connection. If you’re thinking of investing in fast, reliable internet access you can make that investment go further by taking BT SIP Trunk and replacing your existing phone lines.

You’ll also need a phone system. BT SIP Trunk works seamlessly with BT IP phone systems, so if you’re buying a new phone system you should consider BT SIP Trunk as an alternative to traditional phone lines. Not only can the cost savings help you maximise your investment, it can also help you make the most of the IP productivity and functionality features of the new phone system.

But if you don’t have a BT IP phone system or you have an older, traditional phone system you can still have BT SIP Trunk by using our BT SIP Trunk Gateway. This piece of equipment allows the BT SIP Trunk service to work with your existing phone system, giving you all the benefits of BT SIP Trunk without needing to invest in a new phone system.