ADSL Broadband
A keen interest in so-called broadband technology has emerged recently amongst our users. This is no doubt due to BT's rolling programme of upgrading many of their UK telephone exchanges to support higher speed internet connectivity for domestic premises, using existing telephone lines. The most popular technology currently employed is ADSL - Asynchronous Digital Subscriber Line.
A bit about telephone lines
A standard telephone line (sometimes called a POTS or Plain Old Telephone Service line) is designed primarily to convey speech conversations. This is not too onerous a task, as speech information can be accommodated within a fairly narrow band of sound frequencies, usually in the range 30-3000 Hz. For this reason, in communications jargon, telephone lines designed to carry speech are referred to as narrowband circuits.
Analogue dial-up modems
For many years now, in addition to their role of enabling us to make and receive phone calls, POTS telephone circuits have also been employed in narrowband mode to enable connection to the Internet. The analogue (V90) modems which convert digital computer signals into the speech range for transmission are now familiar items to users of dial-up access for e-mail and Internet surfing. While improvements to analogue modem technology have been made over the years, the speed of an analogue modem connection is typically limited to a maximum of 56 kbps. Typical quibbles from dial-up internet users are that the transfer speed is too slow and that their telephone lines are tied up during a session, so it is not possible to make or receive telephone calls while the session is active.
Broadband technology
Technology which can squeeze better performance out of our existing telephone lines is therefore welcomed. Vastly improved data transmission techniques now mean that it is possible to achieve much greater transmission bandwidths over telephone copper wire pairs. In contrast to the narrowband 56 kbps rate, the ubiquitous POTS telephone line can now be upgraded to support broadband transfer rates of 512 kbps, or even 2 Mbps (2000 kbps). Download transfer rate is around 10 times that of a V90 modem, a very noticeable improvement. Upload transfer rate is lower, and works out at around twice that of a "flat-out" analogue modem. The speed asymmetry is due to the higher cross-talk at the BT Exchange end of the links, where large numbers of subscribers' lines converge.
With the new ADSL broadband upgrade, use is made of the additional bandwidth to allow a standard speech circuit to co-exist simultaneously on the same pair of wires as a fast computer network connection. This is achieved by placing compact filter units at the ends of the broadband link, which separate out the speech and computer data signals, which are then fed to the appropriate equipment. Upgrading existing phone lines to broadband has therefore become very popular.
A large number of broadband suppliers now exist within the UK. See for instance:
http://www.adslguide.org.uk/isps.asp?action=summarylist
Can I get Broadband at my house?
BT tell us that ADSL Broadband is unlikely to ever be available in rural areas, where they cannot justify the cost of the infrastructure. However, the technology has become available in all the larger metropolitan areas, and is now being installed in a considerable number of smaller towns and villages throughout the UK. You can check broadband availability by entering your phone number (or postcode) at:
http://www.broadband1.bt.com/mini_check_preorder/step1.asp
How much does Broadband cost?
As with most things, you get what you pay for. The cost depends on a number of factors, including:
- the particular broadband supplier chosen
- how much of the installation you are prepared to do yourself
- the speed of the connection
At the high end of the scale you can pay to have everything done for you equipment-wise, and you could for example opt for a faster 2 Mbps connection. Installation would then cost you in the region of a £500 one-off charge, followed by monthly service rentals of about £200.
For reasons of cost, it is to be expected there will be a higher degree of interest in the "wires only" broadband options. Accordingly, we have discussed the lower cost ADSL broadband options with one of our University telephony suppliers, Thus plc. Thus plc owns Demon Internet, a supplier of UK broadband services, and we have recently begun testing a set-up based on their Demon Express Solo service (£24.99 per month). See:
Can I connect via Broadband to the St Andrews network?
No, not yet. However we are currently carrying out experiments and so far the results are encouraging. We have used a Cisco 827H broadband modem incorporating a 4-port ethernet hub for the test. Three PCs with Windows 98, 2000 and XP versions installed have been connected to the Cisco, using NAT (Network Address Translation) protocol on the user network side.
More details will be announced as the tests progress. It is hoped that we will be able to provide comprehensive advice and support documentation as a result of carrying out the tests.
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