Speed is not everything in a modem

Subscribers will need a fully digital connection to the Net if they are to make full use of it; the old technology is too slow

Modems are a cheap and easy way to connect to the Internet, but they are by no means the most efficient. A modem converts a computer's digital signal into a sound that a phone line can carry. At the other end of the line, the Internet service provider uses a modem to convert the signal back to digital data.

Modems can now reach speeds far beyond what anyone predicted even five years ago, but most people in the industry accept that any future improvements will need a fully digital connection between subscribers and the Net.

Services such as CD-quality sound or real-time, interactive video can be part of a Web site now. The problem is that ordinary modems are too slow to deliver the multimedia to people's homes.

Internet companies have a vested interest in faster access: movies, interactive databases and live games are just some of the products that will enable them to make money in the consumer market-place. At the same time, telecommunications companies see the Internet as one area where they can create a rival service to that of BT.

The result is a list of technologies that reads like a science-fiction novel: direct satellite links to PCs, modems that use radios, devices that download Internet pages via a TV set.

For now, there is something of a gap between science fiction and science fact. Although there are trials for most of the new technologies, there are only two that an ordinary Internet user can subscribe to now.

The first, and the easiest, is ISDN 2. ISDN is a digital phone line that uses BT's ordinary copper wires. BT can supply ISDN in most of the country (a few cable companies are also offering the service), but it costs more than an ordinary line to install, and to rent.

The cheapest ISDN package from BT costs pounds 199 to install, and then pounds 133.75 per quarter to rent. You have to take the line for two years, but the price includes pounds 105-worth of calls a year. A standard ISDN 2 package includes two channels - the equivalent of two phone lines - which can be used together or separately. Each channel has a maximum speed of 64,000bps, which is faster than even the newest 56K modems. And, unlike 56K modems, the full speed works in both directions, not just for downloading information. Anyone who sends information, perhaps because they design Web pages, is better off with ISDN.

ISDN in this country is more expensive than in Europe, but the good news is that hardware prices are falling. ISDN will not work with a standard modem, but a terminal-adaptor costs around pounds 300. Usually, these have ports for connecting ordinary phones and faxes, too.

One disadvantage is that not all Internet service providers support ISDN. Demon is the largest ISP with ISDN access for ordinary customers. Others are trialling the service, and there are a number of Internet companies that specialise in ISDN, albeit at a higher price.

The current step up from ISDN is a leased-line connection. This means a subscriber's computers are hooked directly into the Internet, usually over Ethernet networking. A leased line starts at the same speed as ISDN - 64,000 bps - but far faster connections are available from Internet companies such as UUNet Pipex and BT Internet.

With a leased line, there are no call charges; the disadvantage is the cost. This varies depending on the size of the network, where it is in the country, and the Internet provider, but pounds 10,000 is a realistic installation cost. Even so, a small business that uses the Net heavily may find that a leased line saves money.

For personal users who do not want ISDN, the alternative is to wait for one of the newer technologies to take off. The most likely is access via a cable TV company. Nynex and Telewest are carrying out trials with "cable modems" with their subscribers. In the US, cable modems are already close to ISDN or modem prices. These devices are not modems at all, but digital adaptors that let a computer send data over the cable TV system at very high speeds, up to 5mbps. Potentially, speeds could reach 40mbps. However, not all the country is wired for cable; not all cable operators are interested in the Internet; and, in some cases, the networks are optimised for downloading information (TV programmes). This means that older cable connections may suffer from similar restrictions to those of 56K modems: they are good for Web browsing, but far slower for sending data to someone else.

Telecommunications experts predict that both cable modems and ISDN will give way, in time, to a new network called ADSL. ADSL is based on techniques developed by companies including BT for video-on-demand (where users could download movies, rather than walk to the local store). ADSL has one great advantage over other technologies: it works over existing phone lines.

ADSL can carry up to 8mbps to the subscriber's home, and 64,000bps (ISDN speeds) back to the Internet. Also, the same line can be used at the same time for phone calls.

Telecoms companies are already working on ADSL, but it will be at least 18 months before it is available in any quantity in Europe. Even so, the market appears to be there: the US research company Dataquest predicts 510,000 lines world-wide by the end of next year, and 5.8 million lines by the millennium. If the Internet continues to grow, many of those lines will be rented by Web surfers.