By Mark Ward
Technology Correspondent, BBC News website
BT is to withdraw Integrated Services Digital Network (ISDN) services from consumer use later this year.
Some old technologies are proving very useful
ISDN proved very popular with people working from home who needed access to data connections faster than available dial-up modem speeds.
"We are withdrawing consumer ISDN," said a BT spokesman, "the demand for it has dived with the availability of cheap, fast broadband."
But some broadcasters feel the service is still essential to their jobs.
Back when home net users relied on dial-up modems and fast data pipes were so expensive that only businesses had them, ISDN emerged as a hugely attractive alternative.
The all-digital end-to-end connection could run at 64 kilobits per second (kbps), both upstream and downstream, and was charged by how long you used it for - just like a fixed phone.
Many home users signed up for BT's domestic ISDN service, which was known as Home Highway, to get at those heady browsing speeds. Also many businesses used it as a back-up for their fixed fast data lines.
But as fast data pipes, broadband to you and me, became more popular ISDN has lost its lustre for those home users.
According to figures from watchdog Ofcom the average speed enjoyed by the 50% of UK adults with broadband is 3.8Mbps - far faster than Home Highway ISDN can manage.
But there is one group for whom ISDN has not lost its attractions - broadcasters.
For them it has proved to be a boon when filing reports away from base. Unfortunately the technology is being discontinued all over the world leaving many broadcasters with a problem of what to replace it with.
Although slow by broadband speeds, ISDN is proving useful
"There's nothing that can replace it," said Gavin Davis, head of Glen Sound which makes ISDN equipment for the broadcast industry.
One of ISDN's advantages, he said, was that it gave the same speed connection upstream and down. But because of the technology used to get broadband into homes this has disappeared. As its name implies Asymmetric Digital Subscriber Line (ADSL) used for domestic broadband lets people download much faster than they can upload
Added to this are some basic problems with the way that IP-based networks, ie the internet, handle data traffic jams.
"For outside broadcast-type work IP just does not work," said Mr Davis.
The problem, he said, was that data sent across the net is all mixed together. There are no guarantees that packets of data will arrive at all or that they will take the same amount of time to arrive at their destination.
"ISDN is extremely useful to us because, unlike IP, it doesn't use contention - the bit rate on the tin is the bit rate you get," said Rupert Brun, head of technology and projects in BBC radio production.
"Compare this with IP where the connection gets slower as the network gets busier," he said.
To cope with busy times some IP-based broadcast equipment inserts delay, or latency, in a bid to help the data stream get through.
Adding delay to data streams can cause problems for live shows
But, said Mr Brun, this causes more problems.
"Latency becomes a real issue for live broadcasts where we need to send output back to a journalist or presenter," said Mr Brun, "if the feed back to their headphones is delayed too much it can be very difficult for them to speak."
It can also stymie scheduling plans in which live broadcasts are supposed to dovetail with planned programming.
Mr Brun said the BBC was trialling IP-based alternatives with local radio shows.
"Developments in IP allow guaranteed levels of service to be established," he said, "but it then costs more."
BT pointed out that although ISDN will not be offered to consumers, it was still available to businesses - both large and small.
Mr Davis from Glen Sound said the European Broadcasting Union was starting to draw up standards to ensure IP-based broadcasting equipment is a good replacement. Some nations such as Sweden, he said, have gone as far as pushing manufacturers to build hardware just for them.
But, he said, the alternatives will take time to arrive.
"It's reasonable to expect that in a few years time the telecoms firms will be able to provide short-term, high-quality, bi-directional IP circuits," said Mr Davis. "They certainly cannot do it now."