Business SIP Trunks - High Reliability UK SIP Trunking

Leading UK SIP Trunk provider Spitfire: Guaranteed Business SIP Trunk & SIP Trunking services for Business SIP Phone Systems :-

    Key reasons to use Spitfire SIP Trunk services:

  • Save over £3,000.00 per year compared with ISDN30e Rental
  • Save over £1,500.00 on ISDN30e Installation.
  • Guaranteed call quality - via Spitfire Ethernet or DSL
  • Keep existing phone numbers, or new UK numbers
  • Best value calls - giving you even more cost savings
  • Ideal for all DR requirements

For further information about how Spitfire can get SIP trunking working for you please enquire here or call Spitfire now on 020 7501 3333 .

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Business SIP Trunking and VoIP services

SIP Trunking allows business customers to lower costs, increase resilience with a Disaster Recover strategy, improve flexibility and use multiple new and existing phone numbers anywhere in the UK.

Spitfire are one of the few interconnected operator and Internet service providers. We provision our own SIP Trunk services over our own Internet and Voice networks – a true end to end solution with all aspects of the service managed by Spitfire. In addition to this we also provide SIP Trunks through another leading UK Wholesale Provider, Gamma Telecom. We use these wholesale SIP Trunks in situations where a customer wishes to use a non-Spitfire circuit, or where Spitfire SIP Trunks are not tested with a particular phone system or application. Having in effect access to two SIP networks allows our customers to have two separate SIP Trunk services all managed by Spitfire. These non-Spitfire SIP Trunks, provided by Gamma Telecom, are referred to as Off-Net SIP Trunks.

Spitfire SIP Trunks are a genuine alternative to ISDN30e – with us providing a managed service covering the IP connectivity, SIP Trunks and number management – exactly the same as with ISDN30e. We take responsibility from day one for delivering a robust business class SIP Trunking solution.

Please note that in common with most business quality SIP Trunk providers, we do not normally accept traffic generated by auto-diallers, due to the adverse impact that this traffic can have on network stability.

Benefits of Spitfire SIP Trunks:

  • Up to 50% cheaper than BT ISDN30e – Rental and Connection.
  • Ideal for use with Spitfire Ethernet Circuits.
  • Shared voice and data circuits will save even more money.
  • Keep your phone numbers when moving – to anywhere in the UK!
  • New phone numbers from any UK dialling code, or use numbers from multiple UK dialling codes – regardless of your location.
  • Porting of BT numbers as well as our own UK-wide number ranges.
  • Multi level Disaster Recovery and Resilience options.
  • Proven interoperability with 3CX, AudioCodes, AsteriskNow, Avaya, Beronet, Cisco, Epygi, IP Cortex, Panasonic, Patton, Sark, snom, Switchvox, , Trixbox, Vega Stream . CLICK HERE FOR APPROVED LIST OF SIP SYSTEMS
  • Significant savings on phone calls.
  • Click here for a further explaination of SIP Trunking

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SIP Explained

Residential VoIP v SIP

While residential VoIP generally means services such as Skype, business VoIP users require the same quality as ISDN30e.

ISDN30e quality is delivered by ITSPs (Internet Telephony Service Providers) who deliver VoIP services using SIP – Session Initiation Protocol.

What is SIP?

SIP is the protocol that controls the call, setting up the call and closing it down. The actual voice media uses another protocol RTP (Real Time Protocol), sent as normal IP data packets, so a conversation is broken down into thousands or tens of thousands of tiny IP data packets, each one carrying a fraction of a seconds worth of conversation.

How can I guarantee call quality?

The key to call quality is that every single IP data packet, with it’s millisecond’s worth of conversation, arrives in the correct order and without any delay, so every packet arrives after the previous one, in a constant stream. To ensure this happens 100% of the time you need an Internet connection that has guarantees covering both up time/availability and quality, in terms of packet loss (packets never arrive), jitter (varying time delay between packets) and delay (how long each packet takes to be delivered).

A key issue is that the Internet Service provider (providing your Internet connectivity) cannot guarantee that your traffic will be forwarded onto your ITSP (providing the SIP Trunks) without further delays, the data may be passing through multiple networks before it gets to your ITSP. Even if interconnects are in place, these may change and your service may suddenly deteriorate.

Using an ITSP that is also an ISP (Internet Service Provider), such as Spitfire, means that the data packets are delivered directly to the voice network and assembled as a telephone call without any extra delay – this guarantees that you have a single provider who, with the right circuit, can guarantee call quality and ensure ISDN30e call quality.

Which Data Circuits should I use?

Standard ADSL is NOT suitable to carry voice – the packets arrive with varying delays, sometimes slowly, sometimes all in a rush, sometimes correctly. When using ADSL, most calls might be fine but if the network suddenly gets congested call quality suffers, or the call cuts out.

Without doubt, the best circuit to use is an Ethernet circuit (EFM/Copper Ethernet or Fibre Ethernet). This is ideal for any business which requires 10 simultaneous calls or more. The same circuit can also be used for data, avoiding the need for a separate leased line or other Internet connection. Ethernet prices start at £179.00 per month.

SDSL and SDSLM is also suitable for voice, and will support up to 15 simultaneous calls. The monthly cost is from £44.00.

Spitfire also offer a Voice approved ADSL which will support up to 4 calls at a cost of £21.00 per month.

The key with all the above is that they are designed to carry voice – hence we can guarantee the call quality on Spitfire SIP Trunks over Spitfire Internet circuits.

As well as offering SIP Trunks Spitfire have a leading hosted PBX solution, also delivered over Spitfire Internet circuits – Spitfire SIP Communicator™ – for more information on this please Click here.

Number Provision

Spitfire have our own numbers allocated on all UK dialing codes – allowing you to have the dialing code you require. Again, this gives us control over your numbers, rather than relying on a 3 rd party as many smaller ITSPs have to do.

In addition to this, any BT number, and numbers from many other providers can also be ported to our network – allowing you to retain your current phone number when moving premises.

One of the great advantages of SIP Trunking is the ability to have numbers from any dialing code delivered to your office – regardless of it’s location. You can therefore have a mixture of London and Glasgow numbers delivered to an office in Birmingham – as well as local numbers – ideal if you want to give a local presence to your business.

Backup Options

SIP is ideal as a Disaster Recovery (DR) solution , with multiple levels of resilience.

The first level of resilience is the ability for SIP calls to be routed to a different IP address, i.e. a back up Internet circuit, or a circuit at another location.

The second level of resilience is to be able to divert calls to a back up ISDN30e or local telephone numbers – this can be done on a DDI to DDI basis. Most users will not even know there is a failure. As an alternative, or if you don’t have back up lines on site we can forward calls to multiple external numbers, again this can be done on a number by number basis, do individual DDIs can route to home or mobile numbers on a person by person basis. This is ideal if you are concerned about your main site being inaccessible or inoperative.

Any number on the Spitfire network can be forwarded to any other location – as long as it is connected via a SIP Trunk or a normal telephone line.

The ability to provide Spitfire SIP Trunks and Off-Net SIP Trunks via our wholesale partner, Gamma Telecom, can be used to introduce another level of resilience into the solution.

This DR flexibility is just not available with ISDN30e - please discuss with us your requirements and we will construct a DR plan that suits you.

Why Spitfire SIP Trunks?

  • Spitfire runs its own core network infrastructure to implement our SIP Trunk service.
  • We can provide telephone numbers from geographic areas all over the UK and route them to your SIP service, enabling you to have a virtual office anywhere.
  • Our SIP trunking has flexible options for providing backup to ISDN lines and vice-versa , and further options to forwarding to mobiles/home numbers.
  • Spitfire can provide all the components necessary to connect your telephone system via SIP Trunks including quality IP access and gateways, including on site engineering.
  • We take responsibility for delivering your SIP Trunking solution from the day you place your order, including the circuit, numbering, back up and engineering.
  • With our dedicated test facility we have tested our service with a wide range of manufacturers’ SIP devices. CLICK HERE TO SEE A LIST OF APPROVED AND RECOMMENDED SIP TELEPHONE SYSTEMS .
  • Please note that where we need to provide wholesale Off-Net SIP Trunks via our wholesale partner we do not have the same level of co-operation with the telephone system manufacturer and you will need to configure your system to work with the SIP Trunks.

Cost Comparison – Spitfire SIP trunks and BT Retail ISDN30e

10 ISDN30e lines and 100 DDI numbers, Spitfire SIP Trunks are 53% less expensive – with a wide range of back up options:

  • One year BT Retail ISDN30e with 10 channels and 100 DDI quota plus CLIP - £212.31 per month.
  • Spitfire SIPStream SDSL 2Mb 1:1with back-up ADSL circuit, 10 SIP trunks and 100 DDIs - £99 per month.
  • Saving over £110 per month, with guaranteed ISDN30e equivalent quality.

30 ISDN30e lines and 200 DDI numbers, Spitfire SIP Trunks are 47% less expensive – with a wide range of back up options:

  • One year BT Retail ISDN30e with 30 channels and 200 DDI quota plus CLIP - £602.06 per month.
  • Spitfire 3Mb Ethernet circuit, 30 SIP trunks and 200 DDIs - £320 per month.
  • Saving over £275 per month, with guaranteed ISDN30e equivalent quality.


  • SIP Internet Bearer Circuits - Spitfire Business 2Mb 1:1 SDSL – from £35.00 per month(for use with Spitfire SIP trunks)
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