This article is more than 1 year old

Silent bandwidth battles at BT

You will not unplug that ISDN

Column We could have a nice little fight building up (in a quasi military sense, too) between BT and the armed forces, because of BT's "secret" plans to close down its legacy ISDN digital network.

The reason it's military, sort of, is that BT is still full of soldiers.

OK, that's not literally true, but it's effectively the case: an awful lot of BT's senior executives have military rank, ex officio, as befitting their strategic importance to the country's military communications network.

And if you need to know why the country's military needs BT when they've got wonderful, marvellous, amazing things like GTN or MTN, then you've clearly never seen GTN or MTN.

Anyway, BT wants to can ISDN. It means BT has accepted that digital networking is all Internet Protocol, and all voice is VoIP, and the few ISDN switchboards that are still out there could be served quite readily by installing something like Patapsco's rather nice system for turning IP traffic into TDM and back. And Ethernet is probably all anybody wants.

End of argument, most people would think. As one sysadmin type muttered grumpily in the bar last time I was propping up the counter: "The writing's been on the wall..." and another piped up: "The twenty-first century network, 21CN will do everything the old digital network did", and a third said: "Old news." - and yes, it's been a while since anybody actually ordered an ISDN link except in vastly rural areas where DSL couldn't reach, and a leased line was uneconomic. And that applies to the data network version, ISDN2e, as well.

Say that in public and you'll get a loud cry of "Oh, no, you don't", from some unlikely sources.

The queue of people who will line up to see who can scream loudest probably starts with the police national computer (PNC) which would probably go offline for a month if it lost its ISDN links (says my source) - which sounds unlikely, because last time I looked it was a pitifully small system, capable of handling well under 1,000 simultaneous enquiries. But that's what I heard, from people who should know.

It goes on. The Driver Vehicle Licensing Authority (DVLA) still uses bags of ISDN connectivity. As indicated above, so do several military centres, and if I tried to tell you which ones, I'd probably be exiled to Malta and given a 1200bps Hayes modem as my only link to the World Wide Web, so I won't.

Now, the question several people are trying to answer is a simple one: "Why on earth are all these people using an obsolete technology?"

Part of the reason is exactly the reason why BT would quite like to get rid of it - it is uncontended (i.e. no one has to share it) data bandwidth with very low latency, but (for what it is) incredibly cheap. People look scornfully at its 64 kilobit by two channels bandwidth of 128 kb/s and laugh. What they don't see is that you get that 128 kilobits all the time, without packets being dropped and without contention from grockles doing bittorrent uploads.

Providing that bandwidth over a single twisted pair was economically good business for BT in 1980. It's rotten use of backbone in 2007.

But even if you could provide the signalling and interface "presentation" of ISDN to customers today, you'd have trouble replacing what ISDN is famous for: working.

As one veteran of the business told me: "It's like those old HP 3000 minicomputers. People installed them way, way back and they haven't touched them since. I know of ISDN2e installations that went in before 1980, which did a simple once-a-day dial to the ISDN link at head office, transferred a batch of data, and hung up; and they're still doing it 30 years later."

And the problem is, if you change a thing, the software behind it might stop working, and nobody knows what it does or how to adjust it if it stops.

"I went into one of our clients," said a sysadmin at a large software company which handles vehicle tracking applications. "We asked where the gear was, and nobody there knew. We had to track the cables and, eventually, under a load of old rags - literally - we found this HP3000 connected to the ISDN socket, working. It's been doing that for decades!"

Of course, once 21CN is widely deployed, and once all the out-dated military systems software is updated, tested, and hardened, it will be a doddle to transpose all these systems to new hardware, plug them all together, and carry on. And of course, 21CN will be at least as reliable as ISDN2e was. And I am Marie of Rumania...

But until my coronation, expect BT to be instructed, quite clearly, that unless it can arrange parallel working, it is not going to close down ISDN, or stop supplying equipment to people who use it. And finally, don't expect to read anything of this in the press. The dispute will be as silent as a pike swallowing a duckling - barely a ripple on the surface... ®


BT has been in touch to say they are definitely not pulling ISDN. Well, not all of it.

This is what they said:

Following speculation that BT is to withdraw support for all ISDN services with the roll-out of its 21st Century Network, BT would like to reassure its customers that it remains absolutely committed to the support of major ISDN services and will continue to support ISDN now and in the future. BT's existing ISDN2e, ISDN30e and ISDN30DASS products are being migrated to the 21CN platform and are available to customers today.

While BT is in the process of withdrawing a small number of ISDN variants that are in market decline, namely Home Highway, Business Highway, ISDN2DASS and ISDN30i.421, BT is working closely with its customers to offer a range of options around alternative or replacement products. These include the 21CN compatible ISDN products, broadband and PSTN services.

You could of course go to the BT website for more, but it does seem a little lite on ISDN info, unless you use the search box. Still, it does carry this update. There, isn't that all reassuring.

More about


Send us news

Other stories you might like