SIP Audio Codecs

Connect between devices with Opus and


Remote Podcast Interview

NAB Show, Las Vegas


ipDTL for Radio Remotes

Capital FM, UK


Townsend Coleman - Voice Actor

In:Quality @ NAB Show, Las Vegas

Worldwide ISDN Switch-Off

For some years, ISDN has been the technology of choice for voice sessions and remote radio broadcasts. This is rapidly changing as telecoms companies pull the plug on ISDN, and broadcasters switch to SIP.

This page documents the worldwide ISDN switch-off.  Please comment here with any amendments or additions.

What is replacing ISDN?
– SIP is the protocol which most office phones around the world use to talk to each other. A version of that protocol has been adopted by the EBU to replace ISDN for interoperability between broadcast quality IP audio devices.
ipDTL and allow ISDN equivalent audio to be sent and received over the internet with improved audio fidelity, thanks to the Opus codec.

United Kingdom

In September 2019, BT Openreach removed the ability for ISDN subscribers to make 64k audio and data calls to international destinations including the USA.  They will stop taking orders for new ISDN installations this year (2020), and plan to completely switch off the national network by 2025.

United States

In many states, it is already impossible to order new ISDN circuits. AT&T and Verizon have been pushing up line rental charges for some time for existing BRI customers. In 2017, Sprint switched off their Long Distance ISDN network, with Verizon (formerly MCI WorldCom) serving only legacy customers. The country’s largest radio group iHeart Media migrated all of their stations from ISDN to SIP in 2019.

At the time of writing, AT&T’s Global ISDN (GISDN) service continues to serve Long Distance domestic and international ISDN calls.


In 2018, Telstra stopped selling new ISDN services. They are currently disconnecting remaining ISDN customers, and expect to have completed the process by 2022.


Somewhat ahead of the game, Telia Estonia switched off its PSTN network (including ISDN) back in 2016, having migrated all customers onto VoIP.


Although the country had relied on ISDN for most of its fixed landline provision, the network had been mostly decommissioned by the end of 2018.


Makedonski Telekom no longer sell or maintain ISDN connections.


KPN began closing down its ISDN network in phases in September 2019. They expect the work to be complete by Spring 2020.


Slovak Telecom no longer sell or maintain ISDN connections.


Our logs show that the last successful call from our BT lines in the UK to a Telefonica ISDN line, was in August 2019.  The last such call from our USA facilities, was in March 2020.  Since then, all of our attempts to call ISDN from outside Spain have failed.


The ISDN network was switched off by Telia Company in the late 2010s. Sveriges Radio now use SIP for all external audio contributions.