Trunk Networks deliver 3CX ‘phone systems to business throughout the UK and is able to provide your business with SIP trunks and number porting. We own and operate our own network with 100Gb connectivity at our core. As an ISP we are able to provide the internet connectivity to deliver your SIP trunks too. We have successfully migrated many businesses from “on premise” (a platform that resides at your business premises) to a hosted ‘phone system (either fully managed by us or by our customer’s I.T.)

SIP and VoIP – what’s the difference

SIP stands for “Session Initiation Protocol” and it is a communication protocol that is used for managing multimedia communications, such as voice calls. SIP  is one of the protocols that enables VoIP (Voice-over-IP) and it defines the messages that are being sent between two or more endpoints. VoIP is a method and group of technologies (including SIP) for the delivery of voice and multimedia sessions over an IP network.

Example – On Premise PBX

If you have an on premise IP PBX your PBX is responsible for the call handling, voicemail etc but you will have a SIP trunk (or trunks) to a SIP provider and these SIP trunks are delivered over an internet connection. This could be a dedicated broadband connection or a leased line. The SIP trunk provides the connection between the PBX and the public telephone network but removes the need for legacy ‘phone lines (PSTN, ISDN etc). Many businesses still have a legacy analog or digital ‘phone system. If replacing the ‘phone system with an IP ‘phone system isn’t an option there are VoIP gateways available that enable legacy systems to connect to SIP trunking services and then benefit from VoIP

Example 2 – Fully Managed, Hosted IP PBX

This is Trunk Networks preferred deployment and is the solution that we deploy most of. Internet connectivity has got so much faster and reliable internet connectivity is cheaper than its ever been.

As your VoIP provider we handle everything. The only thing you will need are the IP phones on desks (which we can supply) and a reliable, secure internet connection with sufficient capacity to support the number of concurrent calls your business typically makes. We charge £5 per extension per month and this includes all of the things you would expect from a modern ‘phone system. More information on our hosted 3CX VoIP platform can be found by clicking here – Trunk Hosted VoIP


How will the ISDN switch off affect your business?

The trusted old Public Switched Telephone Network (PSTN), with its Analog lines, ISDN BRI, E1 or t1 lines, are gradually being replaced by IP telephony. An increasing number of businesses are using more modern and flexible SIP Trunks.

The major telecom providers are fast phasing out the old PSTN functionality, and are moving customers to IP. Many European countries have already completely phased out ISDN with countless others to follow. The majority of businesses these days are already using modern IP phone systems and SIP trunks, although some smaller business may still rely on outdated technology.

Phone companies like Verizon have phased out ISDN in the U.S. and in the UK, ISDN lines have significantly decreased. In 2017 major telcos such as KPN, France Télécom, Deutsche Telekom, Telecom Italia and BT began to phase out ISDN lines, with the UK announcing that their entire ISDN infrastructure would be retired by 2025. BT will stop taking new ISDN orders in 2020. BT will continue to support existing ISDN customers.

As a result Session Initiation Protocol (SIP) trunking has increased dramatically, with an expected 71% of all network traffic for SMBs and enterprise customers in the UK expected to be SIP by 2020. The SIP Trunking service is usually provided by an internet service provider (ISP). Unlike a PTSN provider, the lines provided are not physical lines, but a service provided over your internet connection. The SIP Trunk Provider provides phone numbers and lines, usually at better rates than the traditional providers and with more flexibility and shorter contract durations.

This guide explains what SIP Trunks are, their advantages and how you can make the move.


sip trunking

What are SIP Trunks?

A SIP trunk is the modern day equivalent of a T1 trunk. Where in the past you would buy a T1 trunk from a Telco provider and connect it to your legacy PBX / ‘phone system, (to avoid confusion PBX and ‘phone system are one and the same. We will use the term “phone system”) today you can buy a SIP trunk from an ITSP (Internet Telephony Service Provider) and connect it to your VoIP/IP ‘phone system. SIP trunks use the SIP standard. The name ‘trunk’ comes from the telecom world and it means, more or less, a group of phone lines.

Using this standard protocol, telecom service (VoIP) providers connect one or more channels to the customer’s ‘phone system. Phone numbers and DIDs are linked to the SIP trunk. In many cases numbers can be ported to the SIP Trunk.

Benefits of SIP Trunking

Our farewell to the PSTN brings many benefits. SIP Trunks deliver:

  • Lower monthly Line & DID Rental – The monthly fee to have a number of lines installed at your office drops significantly with SIP Trunks. And DIDs cost a lot less.
  • Lower call charges – There are many SIP Trunk providers and competition has driven down call charges significantly. Some SIP Trunks even come with unlimited calling and you can save on international call charges, too.
  • Better customer service – Provide better customer service by adding more geographical and international numbers. Quickly and easily add numbers to your SIP Trunk and terminate them on your IP ‘phone system – you can give customers more options to dial in at a significantly lower cost, even long distance. Customers can contact you more easily and sales will increase.
  • Move offices and keep the same number – SIP Trunks are not bound to a location, so it’s easy to move offices without having to change your stationary or inform your customers. There is no longer any need to pay to forward phone calls to the new offices.
  • Eliminate VoIP Gateways – SIP Trunks will eliminate the need to buy and manage VoIP Gateways. All phone calls come in via IP. No extra conversion often means better quality too.
  • Leverage a modern IP ‘phone system – Modern IP ‘phone systems will give customers increased productivity, mobility and boost sales. Connecting an IP ‘phone system to SIP trunks is much easier than via the PSTN. You can go on-premise or hosted, the choice is yours.
  • Flexibility – It is easy to add channels to your SIP Trunk to cope with increased calls. A simple phone call will allow you to add channels, and often this can be done immediately. Compare that to the delay in having additional lines installed and then having to upgrade your old ‘phone system to handle more lines!
  • Correct number of channels – With SIP Trunks, you can easily choose the correct number of channels that you need.

Selecting the right SIP Trunk provider

The next step is to choose a SIP Trunk provider who will supply the necessary SIP Trunks. A few factors come into play when making this decision:

  • Security – As SIP Trunks are exposed to the Internet, it is very important that the SIP Trunk has a well secured network and an anti-fraud system in place. The anti fraud system must monitor the system and provide protection against call fraud.
  • Own network – Does the SIP Trunk provider run its own network or is it a rebranded service? There are quite a few providers out there reselling SIP Trunks from other providers. Select a provider who has control over their service and network.
  • Number Porting – Can the provider port your phone numbers? Ensure that you choose a provider who can port all the existing numbers – not all providers are able to do this for all regions.

Upgrading Internet connectivity

Once you have selected your SIP Trunk provider, consider a dedicated Internet line for the SIP Trunk. Most firewalls are able to handle multiple WAN connections, and, considering the low cost of an Internet line in most places, a separate VoIP connection will be the most reliable way to ensure the quality of your VoIP calls.

However, some SIP Trunk providers bundle their service with a dedicated Internet line. This keeps your voice traffic separate from your data traffic. Much will depend on the cost and your network infrastructure. Check that your firewall is up-to-date and will be capable of handling VoIP traffic correctly.

Upgrading the ‘phone system to an IP ‘phone system

Chances are that the old PSTN lines are connected into another old device, the hardware based phone system. This device is inflexible, difficult to manage and often expensive to maintain. Technically it is possible to buy a gateway that allows the old ‘phone system to talk to the SIP Trunks. But why not upgrade to a modern ‘phone system leverage the flexibility and modern features IP telephony can bring to your business phone system. This allows you to take advantage of the cost savings, easy management, and productivity increases that an IP ‘phone system offers.

We have many customers who used to have an on premise hardware-based phone system. We have successfully migrated them to either a fully managed, hosted solution, or a hosted solution managed by them.