Dealing with the great ISDN switch off

The telephony network is undergoing a major transformation with the end of the ISDN network. Throughout Europe and beyond, service providers are switching off their ISDN networks and migrating their customers over to SIP trunks.

One by one, the incumbents will be switching their ISDN network off over the next decade. The first service providers have already made the switch, including Slovakia and Macedonia. Most have made their plans public, including Swisscom (2017), Deutsche Telekom (2018), Orange (2020) and BT (2025).

For service providers, the migration is inevitable, as they don’t want to operate two separate networks – a TDM one for voice and an IP network for everything else. This is a significant undertaking – in the UK for example, BT operates 3.2 million ISDN channels.

But this move isn’t just a benefit for service providers, switching over to an all-IP network also allows enterprises to ditch their voice connections and gateways to enable the full convergence of voice and data.

Moving to SIP trunks

SIP trunks have been around for a number of years, and are essentially IP telephone line trunks from the enterprise telephony system to their service provider. They allow enterprise users to make calls to other parties outside of company network.

SIP Trunks can be terminated anywhere on the enterprise network rather than locally, like ISDN. For example they could be terminated in the data center to help consolidate communications across all sites. There are a wide range of benefits to using SIP trunks over ISDN, including convergence, cost savings, integration with cloud services and resilience.

The main barrier to moving wholesale over to SIP trunks has primarily been a regulatory one because it is a voice service. This has meant that SIP trunks have been primarily used by service providers to deliver international calling, while the incumbent has continued to offer local services such as local calling and emergency calls.

However telecommunications regulation is changing in many countries and service providers are now able to offer a full-IP service which includes local inbound and outbound calling. For example, Orange Business can currently provide a fully-unplugged service in 24 countries and territories. This means that there is no need to wait for the incumbent service provider to switch off their ISDN network to make the move to SIP trunks.  

To help enterprises make the switch to SIP trunking Orange Business is producing a range of different materials covering the issues to the business case. For more information head to