6 Steps to Setting Up SIP Trunking

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The death knell for ISDN has been rung.

Integrated Services for Digital Network (ISDN) is unsupported and old-fashioned, with little investment in existing lines likely to occur from now on, and so BT plans to phase ISDN out completely by 2025. It seems to be an essential move for businesses of all sizes to switch to the more sophisticated SIP system as soon as possible, but the switch to the next big thing in Telecoms is slower than it should be.

A survey by Timico revealed that 67% of IT managers didn’t even know what SIP was. Here we show you the benefits of SIP over ISDN, the essential points when considering which trunking system to purchase, and the 6 steps to setting up SIP trunking easily.

Why should I migrate from ISDN to SIP Trunking?

SIP trunking is a VoIP and streaming media service that works by messages being sent between endpoints, which administrate the establishment, termination and other elements of a call. As well as voice calls, SIP has the advantage over ISDN by facilitating video calls and instant messaging.

The key feature of SIP is the removal of physical hardware, namely phone lines. This removes the cost of hardware – ISDN connections rely on expensive circuit installs, whilst SIP runs on a simple data circuit via IP connection.

SIP calls are also generally cheaper, as ISDN-based calls are charged at standard network rates. Call routing through SIP is usually much more economical, even with international calls. Data connection prices are gradually decreasing, whilst IDSN prices have not changed for years.

The lack of hardware also allows the service to be powerful, scalable and very flexible. The lack of physical aspect reduces the restrictions around call capacity and location. The fact that the phone lines are virtual rather than physical allows SIP to be scaled easily, and means the calls are cheaper than traditional ISDN lines. The lack of hardware also allows SIP systems to move around more easily, which is essential to keep up with the ever more flexible working schedule of modern business.

The nature of business now means that more and more employees are shifting to remote working. Unlike ISDN, SIP accommodates working remotely, and enables users to have calls made to their desk phone automatically delivered to their PC or smartphone without being hampered with forwarding charges.

SIP also lets your business remain operational if a line is busy or your office is hit with unforeseen circumstances such as weather disruptions, fire damage or network failure.

6 Steps to Setting up SIP Trunking

1. Size your IP connection
The scale of your system depends on how many callers you need connected at once. This can be easily done whether you only need a few users at once, or whether you require the simultaneous connection of hundreds of lines.
2. Setting up phones
This involves configuring SIP to the network, which can be done by connecting a SIP trunk to your IP PBX or PBX gateway. This step also includes checking that there is enough bandwidth and a strong enough connection to handle the system’s scale as agreed in the first step.
3. Boosting resilience
This is done with disaster recovery procedures, which let SIP calls be immediately redirected without service disruption, such as incoming desk phone calls being rerouted to a PC or mobile device.
4. Plan to port the numbers
Transferring numbers from one system to another is usually possible between the main telecommunications companies, but of course it’s important to check.
5. Testing the system
Before porting the numbers and going live, the set-up needs to be tested, and any connectivity, LAN, WAN and firewall concerns need to be solved.
6. Securing
Safeguard any potential security issues by examining firewall, system and user account passwords.

What Should I Consider When Looking At A New SIP Trunking System?

The most important thing to try to judge is what features your business requires from a SIP provider, and which solution suits your needs the most comfortably. A cheap, simple SIP provider is enough if all your business requires is the ability to make calls for less money. However, your needs may necessitate a comprehensive, versatile service that offers a selection of add-on features.


Reliability is one of the major selling points for SIP, but not every provider may be able to completely keep you covered in case of network failure. You should check the call routing and failure provisions of any potential SIP provider to make sure the necessary preventative measures are in place for you to retain uptime, even when the network goes down. You are more likely to find a reliable SIP system if you look for a provider that uses direct interconnections with tier 1 providers, as opposed to one that buys their connections and routes from intermediate carriers. This is because in the event of a network failure, a provider that uses intermediate connections and routes has to contact the reseller to find out why the failure occurred.


SIP has its advantages from being run over the Internet, but this has its problems too, particularly with security breaches and toll fraud. You should try to find out what security measures your provider offers before purchasing anything. This can include call barring, which lets you block or restrict access to certain countries or locations. Call barring gives you total control of your traffic and prevents hackers making expensive calls through your phone system. Some of the best SIP trunking providers feature algorithms that are specifically designed to monitor fraudulent actions, and immediately step in and shut any such activity down.


The pricing model you select will have a direct impact on the telecoms budget, so choosing the right model for you is a big decision. Two of the most popular pricing models are Port-Based Pricing and User-Based Pricing. Port-Based Pricing means that a company pays from an estimation of what their peak volume will be. A User-Based model involves paying a flat fee for all the users, regardless of call volume.
There is so much to consider before choosing and setting up a SIP system, and it’s a decision that can potentially save you a lot of money and dramatically improve your business processes. However, wading through all of the possibilities to find the right solution for you can be time-consuming and costly. Wouldn’t it be better if someone else could do it for you?