Battle of the bandwidths


Modems have always been the primary way of connecting to the Internet for the home user. Ten years ago, however, modem owners were at the cutting edge of communications and were probably considered freaks and nerds. Now, though, if you lack access to the Internet you’re considered to be technologically underprivileged; modems have become commonplace technology. Here, we take a look at today’s Net-connection options. In 20 years, modems have evolved from acoustic-coupler modems – via which you attached your telephone handset to the modem – capable of from 300 bits per second (bps) to 56Kbps. Beyond the modem, digital-communications methods, such as ISDN and ADSL, have taken transfer rates to new heights. The latest technology, ADSL (Asymmetric Digital Subscriber Line) is in its infancy and its mettle remains untested. Much of the UK’s telephone system is now mostly digital, yet the short hop from your street’s junction box to your phone wall-socket is still analogue. Because your computer’s outgoing signals are digital, the modem has to turn these into analogue. These remain analogue only as far as the junction box, after which they zip across BT’s digital network and remain digital to your ISP (Internet Service Provider). So why does the digital network go only to the corner of your street? Well, you can get BT to make the analogue bit digital, but this wholly digital connection is called ISDN (Integrated Services Digital Network); the consumer version of this is called Home Highway, and costs more than a normal telephone line. The customer is footing the bill for BT’s completion of the digital network through extra line rental. Forward-looking countries such as Germany saw the benefit of a completely digital network years ago, and actually gives a discount to those using ISDN. Because they relay analogue signals, the fastest a modem can go is 33.6Kbps –the physical limitation of analogue lines. However, most modems now claim a speed of 56Kbps. This is possible only when connecting to an ISP, because the signal becomes digital only after you get past the end of your street. Before the Internet took-off, modems were used to transfer files between individuals, meaning there were analogue connections at each end of the line. A 56Kbps modem cheats, by using the digital bit of the line for fast downloads, but it still can’t get the upload speed beyond 33.6Kbps. And anyway the 56Kbps speed is only a theoretical top speed – in reality, it depends on the line. I’ve never seen a 56Kbps modem connect at any faster than 50Kbps. This means a 56Kbps modem is the ultimate speed – unless you go digital. The easiest way to take the digital option is to add an ISDN terminal adaptor, and subscribe to BT Highway. Completing the digital circuit means you connect at full speed every time. Full speed for ISDN is 64Kbps, in both directions. When you get ISDN you also get dual-lines, so as long as your ISP supports it, you can use both these lines to connect to the Internet simultaneously, making a speed of 128Kbps possible. But don’t forget, using both lines means double the telephone charges. ADSL
ADSL is touted as the solution to all our Internet connectivity problems, promising a high-speed, always-on Internet connection. It should signal an end to dialling-up the Internet, because it’s always connected. ADSL may be the ultimate answer, but, in the short term, it remains on the fringes of mainstream connectivity. The main thing preventing ADSL reaching its full potential is BT, which has made its launch so low-key that few people know what ADSL is, never mind considering using it. ADSL uses the existing copper cabling that connects your normal telephone line to hook-up to the Internet at speeds up to 2Mbps (about 2,000kbps). This requires special equipment at telephone exchanges, meaning access is offered only to those who live in the right areas. These areas are mainly in the centre of large cities; out of town means out of luck. Also, there’s a limit to the distance you can be from any ADSL-equipped exchange. Living more than two or three miles from an exchange means ADSL will be something that only others can enjoy. However, those Macintosh users lucky enough to use ADSL still face problems – using a Mac being the foremost of them. PC users can sign-up for the consumer version of ADSL for £40 per month, with a £150 installation fee. That buys download speeds of 500Kbps, at least in theory – but in practice, users may share that bandwidth with up to 49 others. Mac fans, though, can connect only via ethernet, because no one has yet written drivers for the USB ADSL modem. By connecting via ethernet, you’re considered to be a business user, and, of course, are required to pay business rates. Nice one, BT. The minimum you’ll pay for ADSL on the Mac is £260 for installation and £100 per month (both ex. VAT). It’s no wonder that ADSL isn’t exciting Mac consumers. The one good thing about the ethernet-connected business option, though, is that you have to share your connection only with 19 others, not 49. The reason lines are shared is because of hardware limitations at exchanges. In days of yore, party lines were used to share telephone services with neighbours. If a neighbour was on the phone, you had to wait until they were done before dialling – the only perk being listening-in on their conversation. ADSL uses a similar principal to share bandwidth, with the number of sharers known as a contention ratio. Consumer ADSL has a 50:1 contention ratio, and Business Plus ADSL has a 20:1 ratio. Because ADSL is a nascent technology, you could find yourself being the only person in your exchange-area with ADSL. But as ADSL takes off, it may end up so clogged that you’d be better off with a 56K modem. I hope BT will get its act together and provide better Mac support. However, if reports from the US are anything to go by, ADSL will be suitable only for home use.
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