Gimme bandwidth

Gimme bandwidthThe demand for higher bit rate Internet access is increasing as the Internet enters more and more homes. Steve Bush looks at the technologies that will provide it Is the Internet the best thing since sliced bread or a toy for techno-fashion victims to play with as a substitute for real life? The truth is probably somewhere in between. Certainly many important research projects would hiccup and a lot of people would be inconvenienced if the Internet evaporated tomorrow, but the World would not cease to grow food and the global majority, who do not have access, would not notice at all. Whichever way you view it, the Internet assumes the out-of-proportion importance of a dripping tap when a link drops to a few kbit/s halfway through a 2Mbyte file download. Most connections are made through POTS (plain old telephone service) twisted copper pairs. Once the domain of the 300bit/s teletype, communications through this medium at approaching 56kbit/s are now common – provided data is coming from a fully digital Internet service provider (ISP) under perfect line conditions. The best backward data rate over this kind of channel is 33.6kbit/s which is also the maximum available between consenting analogue modems however sophisticated they are. Neither of these figures, 56 and 33.6kbit/s, are likely to get any faster over POTS as they are on the limit of the equipment that operators like BThave installed. Judging by the rate that 14.4kbit/s modems, followed by 28.8, 33.6 and 56k types have made their forbears obsolete, the hunger for bandwidth into the Internet-addicted home will continue to rise unabated. Whatever comes to replace the 56k modem is going to need an enhancement to POTS, or to replace it altogether. BT’s offerings predictably – as they own so much installed copper – involve boosting the bandwidth of their network. The first thing that home users are likely to get is something BT is calling Home Highway. This is a no-frills version of the ISDN services that businesses use. To add Home Highway, BT changes the user’s interface (called a line card) at the exchange end and installs an access box in the home. Once done, the subscriber gets two 64kbit/s channels to do with as they wish, giving either two voice channels, one voice and one 64kbit/s data channel or one 128kbit/s data channel. Unlike 56k modems, this data rate is obtainable in both directions between suitable equipped users. Anyone taking up Home Highway will get at least 64kbit/s Internet as, according to a BT spokesman: “All ISPs support 64kbit/s, although not all can manage 128.” At the home end, the subscriber plugs their PC serial port into the BT box and gets 64k immediately. 128kbit/s requires an ISDN card in the PC which, reckons BT’s spokesman, costs under ?100. The cost of Home Highway to the consumer is not yet set but will be after a trial now under way in the Midlands. At the moment 100, soon to be 400, homes and small businesses are involved. Introduction of a national service, beginning wherever demand is greatest, is due Autumn. Another way to improve the available bandwidth of installed copper is a group of techniques jointly known as ‘digital subscriber line’. ADSL (asymmetric digital subscriber line)is the best known of these ‘xDSLs’ and promises up to 8Mbit/s data rates over copper when it becomes established. Another type, VDSL, works at 52.8Mbit/s providing the line length is under 1.5km and in good condition. Like Home Highway, the line card at the exchange needs changing and the subscriber needs special equipment to benefit from xDSL. In some cases, including ADSL, the subscriber equipment has to be installed by the telecoms company. With others, which are generally limited to 1.5Mbit/s, the user can install the interface through standard telephone wall plug like a normal modem. ADSL is closest to installation in the UK. Again, BT is at the forefront and is starting a 2,000 subscriber trial in West London this Summer. This will be with 2Mbit/s ADSL (upgradeable to 8Mbit/s) and is designed to establish what services users want and how to charge for it. As part of this trial, BT is in touch with a range of different content providers who will offer services like video-on-demand, home shopping and home banking alongside high speed Internet access. Away from copper POTS, there are several further options to bring more bandwidth into the home. These include cables associated with cable TV, the electricity mains, ‘wireless-in-the-local-loop’ (see box) and optical fibre. Cable is the simplest case and comes in two basic types, Siamesed copper pair and coax. When a co-axial cable is installed to bring cable TV into a household, there is frequently a POTS copper pair attached, in what is called Siamese cabling. It is this pair that enables cable companies to offer telephone services and which provides the ‘back-channel’ for interactive TV services. Using this pair, cable companies can essentially offer any service that BT or any other telecoms company offers over copper. However, using the coaxial cable itself through something called a ‘cable modem’ can open another high rate channel into the home. Cable modems, like xDSL, are only at the trial stage in the UK. Experience from the US suggests that cable companies will be offering up to 10Mbit/s to subscribers through cable modems. (As with ADSL, the data rate back from the user to the service provider is significantly lower than this.) US market research company Forward Concepts has gone so far as to predict that there will be over seven million cable modem units in US homes by 2002. This, it says, will be four times the number of residential xDSL installations. The 240V electricity mains is another connection into the house. Although there is no existing communications network behind it, burial has already taken place removing a major installation cost. Nortel and Norweb jointly have a trial in the North-West where they intend to demonstrate 1Mbit/s access. Running an optical fibre into the home is perhaps the ideal bandwidth-expanding solution. Telecoms companies transfer data in their trunk networks through fibre at 2.4Gbit/s – enough to satisfy the most ardent Web addict. The problem with fibre is expense. Not only does it have to be run to the home, but the interface equipment is costly. Whilst not much can be done about the cost of laying fibre – or coax, or copper pairs – companies like the UK’s Bookham Technology are knocking the cost out the interface. Its products use silicon chip substrates to hold all the optical components required, including the incoming fibre, in alignment. “We make transceivers that will transfer data at 155Mbit/s for under $150,”said Paul Barrett of Bookham. This is still too high for widespread consumer acceptance, but would drop to under $100 in the large quantities needed for mass installation, which is the sort of price the market will be looking for. Japan has the most ambitious plans for fibre to the home, aiming to give all homes in the country 20Mbit/s access through fibre by 2010. Two million homes are expected to be connected by the end of 2000. If demand for higher bit rate Internet access is there, as seems inevitable, there are plenty of different techniques available to provide it. Cost and maturity of available options vary considerably although 2Mbit/s from BT using ADSL looks like the favourite to first bring multi-megabit data into a significant number of UK homes. Internet over the ether To avoid the cost of burying things in the street, Cambridge-based Ionica uses wireless links to put voice telephony services into homes using a system called wireless-in-the-local-loop. This replaces the local loop – the connection between exchange and home – with a radio link similar to a cellular network. Although marketed as a voice system, Ionica guarantees 28.8kbit/s access over its network. The system is called Proximity I and its maker, Nortel, says there is an ISDN (64kbi t/s) version in development. One other possibility that deserves a mention is satellite based data transfer. Teledesic hopes to launch its ‘Internet-in-the-Sky’ over the next few years.
This will be capable of shipping huge amounts of data around the world without anyone having to dig any holes at all. It will however be at the expense of launching nearly 300 satellites into space, so this is unlikely to cause the dawn of bargain megabit data rates to your home.


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