New standard emerges for ISDN replacement

As ISDN slowly fades out, a standard finally emerges, writes Matthew Hardman.

For some years now, BT and their subsidiary Openreach have been threatening to switch off the ISDN network, with 2025 earmarked for pulling the final plug. Over in America it’s already happening, and stations have had to seek out alternatives.

As the internet and broadband provision have improved, the industry has seen increased adoption of IP codecs such as Comrex, LuciLive and ipDTL. Stations have also experimented with consumer apps like Skype and Facetime; with mixed results.

Of course, no such service is a direct replacement for ISDN, which is a standard which manufacturers and telecoms providers have complied with to allow interoperability between different carriers and hardware. Dial an Australian ISDN number from the UK and – assuming the settings match – your broadcast can go ahead.

Step forward SIP, a protocol which is already widely adopted by VoIP phones and company switchboards. The EBU (European Broadcasting Union) actually set a standard for SIP connectivity between broadcast codecs over a decade ago, only it was largely ignored as there were no agreed settings.

The good news for radio engineers, is that with the emergence and gradual acceptance of the wideband, low delay Opus audio codec in services such as ipDTL, there is now a common codec for SIP audio calls.

At the recent NAB broadcast technology show in Las Vegas, all of the major codec manufacturers (Comrex, Tieline, Prodys, Digigram, Vortex, AEQ) were demonstrating products that support the Opus codec and SIP protocol. We’re now just waiting on Telos to add Opus to their Z/IP One unit.

What does this mean in practical terms? It means that a radio station can call any other studio in the world, simply by dialling their SIP address. And assuming both stations are using Opus, there’s no conversation to be had about codecs or settings; which has always been the barrier with ISDN interoperability.

At their stand at NAB Show, UK company In:Quality were demonstrating connections between a range of codecs from different manufacturers with their SIP service

The BBC is slowly making the transition to SIP with its in-house BASS service, with many local radio travel bulletins no longer connecting over ISDN.

Similarly Global and Bauer are making more use of IP codecs such as Comrex, and their wide area networks. Calling in from the outside world can still be a tricky business though, and that’s where SIP comes in.

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