BT has announced that in March it will begin trials of a new data service called Midband. The service will offer an always-on connection and data rates of up to 128kbit/s, and though the carrier is keeping quiet about the details, it appears that Midband will be based on ISDN technology.
ISDN services, such as the Home and Business Highway products and ISDN2, offer two 64kbit/s data channels that may be used for data or voice, and a further data channel running at 16kbit/s that carries signalling information between the user and telephone exchange.
This 16kbit/s channel is called the D channel and is grossly under-used. There would typically be a few hundred bytes of traffic transmitted at the beginning and end of a call, and nothing in-between. It is likely that BT will use the D channel to provide a basis for the always-on part of Midband, bringing in the 64kbit/s channels as required.
This idea has been around in various forms since ISDN was first invented. There was a surge of interest in the early 1990s when a forum was set up to develop standards for what was called Always On/Dynamic ISDN (AO/DI).
Despite being placed under considerable pressure, BT consistently refused to make the D channel available for this purpose but finally announced a service called ISDNconnect in 1998, which offered a 2,400bit/s channel to a specified destination. This was warmly received until the tariffs were published and then, suddenly, almost all the planned applications disappeared. This time round, BT appears to have the pricing right.
Midband should appeal to teleworkers and branch-office sites where the traffic is predominantly email with some Web browsing. The main advantage of Midband is that it can be rapidly provided in areas not equipped for ADSL, because ISDN already reaches about 97 percent of UK lines.
BT has not stated what bandwidth will be available on the D channel, but it could be almost 16kbit/s. This may provide rapid delivery of average text emails, while any large attachments could be transferred to one of the 64kbit/s channels in a matter of seconds. This process would be entirely transparent to the user, who would simply see a 128kbit/s connection with a slight startup delay.
It is interesting to reflect on what difference Midband would have made to Internet connectivity in the UK if the service had been launched five or more years ago. If Midband had been made available back then, the UK could now be the most connected country in Europe - and the government wouldn't need to keep inventing schemes to implement Broadband Britain. ADSL would have been cheaper to install because the infra-structure would have been put in place for Midband. In addition, the general economy and GDP would be in a much healthier state.
There are still several unanswered questions about Midband, such as whether voice calls will be possible on the same line, whether the user will have control of the bandwidth, and whether existing Highway and ISDN2 installations can be upgraded, for instance. However, BT should be congratulated for, at long last, offering a service that can provide always-on Internet connections at a reasonable speed to almost any line in the country.
If only it could have done so earlier.
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