TDM-to-VoIP migration – the 3 vital steps

Published by John Baldwin on June 8, 2016

In a recent report, the analyst house Gartner recommended strongly that enterprise networking leaders combine their WAN and fixed-voice trunk sourcing and plan to migrate to SIP trunks. Many customers we have spoken to are on-board with the imperative and benefits of moving from TDM to VoIP, but they are still concerned with the “how” and “what” of such a migration. So here, we outline the key issues and how we go about addressing them.

When considering migrating to SIP (VoIP), the three main key customers’ concerns boil down to:

  • What will voice QoS do to my network? Will I have enough capacity?
  • Does it support all my voice features ?
  • What’s the fastest and best way to migrate?

To address these concerns, we work closely with the customer to size IP connections based on planned number of users (callers) that need to be migrated.  Voice packets require a small but assured amount of bandwidth, low delay, low jitter and low packet loss. Voice packets are also premium class and can use 50-60% of the total bandwidth but a capacity upgrade will not always be required.

When we get to the actual implementation, there are options. For a smooth and seamless migration, the fastest and safest way is to follow a predetermined plan to make sure the solution is properly designed, configured, tried and tested before even the first site is migrated. And this process need not be complicated or onerous as we have ensured all the standard PSTN features and more are implemented in our SIP Trunking.

Some would go for the Big Bang approach where SIP trunks and all sites are migrated in one step. Big Bang could provide shorter implementation time and condense any migration pain into one time period but we are a strong believer in the following multi-step migration method.

  1. Set up your SIP trunking/VoIP access solution (design and configuration)
    • Define maximum number of concurrent calls, required bandwidth, resiliency options and telephony features.
    • Configure the new SIP trunks. For example, ensure the IP Config on the Colt service and customer SBC (session border controller) are compatible and routing correctly.
  2. Test everything
    • Along with your service provider, test and try everything before the migration date and simulate the migration process in advance.
    • Set-up a reliable roll back plan. For example, Colt offers customers the option to keep both their services (TDM and VoIP) for a certain period to enable roll-back.
  3. Migrate to the new SIP-based solution on a site-by-site basis.
    • Ensure your service provider provides a dedicated project manager for this.
    • Define Migration Day and ensure geographical numbers are working by carrying out immediate inbound test.
    • Repeat for each site – recognising that number porting is a potentially complex process involving 3 parties (customer, provider and legacy provider) and pre-defined service maintenance windows.
    • Be aware that the porting process and regulation vary widely across countries. For example, to smooth this process, Colt has a local porting officer and regulatory expert in each country in addition to its porting agreements with local operators.

Having completed the migration, you can now plan your next step. For example, setting up new locations in Central Europe or supporting your company expansion in the Far East. We would be happy to explain how we are expanding our global SIP capability to meet these needs and share more customer migration stories and experiences. A dedicated e-guide has been produced to assist you in your migration to VoIP. Download it here.

For more information on our SIP capabilities click here.

What's your goal today?

1. Are you on the Colt IQ network?

Our network connects over 31,000 buildings worldwide powering companies such as Hitachi, Atos, Forbes, Arthur D Little, Brussels Airlines and thousands of others. Find out if you're Colt connected now.

2. Learn about digital infrastructure

We've written thousands of guides and white papers, regularly publish content on our blog and host regular events on everything from enterprise network connectivity, to cloud, digital transformation and the hybrid workforce.

3. Join our team

To learn more about joining our team of over 5000 people around the world, and to browse our current open roles visit