The complete guide to wires-only ADSL

With recent price cuts by BT, and more exchanges being converted, we could be seeing the emergence of the first mass market in ADSL.

Although the benefits of high-speed, always-on access are clear, and progress towards widespread availability is promised, in reality the spread has been slight so far.

The government wants the best broadband access of the G7 economies by 2005, but even the most optimistic now recognise this as a pipe dream.

So, why is it taking so long and is it worth the investment in time and money? BT has dominated the market for ADSL services in the UK; it owns the exchanges and has dictated the flow of progress. Not even the government, it seems, can force the behemoth to open up to competition.

Once you've made the decision to go broadband, you'll need to adapt your internet use to suit. A firewall is an absolute must. We'll examine just what you'll need and look at what's possible and what's not with existing ADSL services.

The actual mechanics of ADSL are relatively simple. Understanding the basics of the technology makes it much easier to choose services more efficiently.

Currently, many more people want broadband connection speeds than have them. Barring a major advance in communications technology, this situation won't improve in the short term. However, this guide will tell you all you need to know.

ADSL checklist

The first requirement for ADSL installation is an ADSL-enabled exchange within reach of your location, where 'reach' is defined as the distance over which the service will work reliably.

When BT first launched its BTopenworld ADSL service, only a tiny subset of local exchanges were enabled, mostly in urban areas, and you had to be within 3.5km of the exchange to pass the installation test.

However, all this has changed as BT's attitude to broadband has wavered from the dismissive to the enthusiastic via changes in management.

The first stage would bring ADSL within the reach of two-thirds of the population. Moreover, all new ADSL installations use Rate Adaptive DSL technology to extend the distance from the exchange to 5.5km, rather than 3.5km.

You can check out the availability of ADSL services in your location at www.btopenworld.co.uk by entering your phone number and postcode, but you'll also have to check your distance from the exchange. BT will do this for you once you express an interest.

It's also vital to check that your home phone line isn't using the Digital Access Carrier System (Dacs). This is the modern form of the party line, where a single pair of copper wires is used to carry two voice circuits.

Used by BT where there aren't enough wire pairs to connect everyone who wants a phone line to the exchange, it's particularly common in rural areas. If you have Dacs, then you can't have ADSL, although BT will normally replace Dacs with a proper line when you order the ADSL service (assuming it's available in your area).

What do you need?

Once you know that the service is available, you must decide how you want to use it. The essential first step is to choose an ADSL internet service provider (ISP), which will arrange for your BT line to be converted to ADSL at the local exchange and create an account for you.

However, ISPs need to compete with each other even though they all use services based on BT exchanges, so there's a wide range of options available.

Is your connection going to be used by a single PC for home use? Will you need to connect a network of machines to one ADSL connection? What facilities, such as video conferencing, will you want?

The ISPs have a variety of services to match your needs. They also allow you to change contracts, with possible time restrictions, if your needs change after installation.

With wires-only ADSL, though, most of this is invisible at connection. The modifications to your line are done at the exchange, account set-up is done at the ISP and, once you agree a contract, all you have is the same BT socket you always had with new services attached to it in the outside world. To make use of them, you'll need additional technology, though.

Hard facts

One of the advantages of wires-only ADSL is that you don't have to commit to a particular range of equipment or local network topology when you sign up. However, you do need a minimum set of components to get anything out of the newly enabled socket.

Most essential is a pair of microfilter sockets: a low-pass filter for basic telephone calls and faxes, and a high-pass filter for ADSL.

You can buy these from the ISP for about £10 (ex. VAT) and you should fit them to all extension sockets connected to the ADSL service to prevent any possible interference, even if you'll only be using them for voice calls.

Next, you'll need an ADSL modem or router to plug into the high frequency socket on the microfilter. This choice depends on the type of connection you need, which is often referred to as the ADSL 'presentation'. The cheapest option is an ADSL modem connected to a single PC through a USB socket.

A wide range of these is available from companies such as Alcatel, Eicon and DLink. This is USB 'presentation'. A more expensive option is an ADSL router from companies such as Draytek, DLink and Netgear, which provides a standard RJ45 Ethernet socket for connection to an existing or planned local area network. This is Ethernet 'presentation'.

One other possibility for the experienced user is to set up a spare PC running the appropriate software, often free under Linux, to act as a router. However, this isn't recommended for anyone without a deep knowledge of networking, Linux and probably both.

There are also a few possible quirks in this area. When ADSL first arrived, the Alcatel USB modem or Fujitsu Ethernet router installed by the BT engineer was BT property, so you weren't supposed to tamper with it.

This led to products like Draytek's Vigor 2200USB, which had a USB socket that plugged straight into the USB modem and an Ethernet socket for connection to the wider network.

With wires-only ADSL, that's no longer an issue. Also, choosing USB presentation doesn't prevent sharing the ADSL connection across several networked PCs, but Ethernet presentation is more conventional.

Closing the stable door

Finally, there's one thing you need that the ISP might not emphasise enough: a security system for your ADSL connection. With an always-on connection like ADSL, there's a much bigger opportunity for hackers to reach your machine. It's always worth remembering that, when you're connected to the internet, it's also connected to you.

There are two main approaches to security, depending on the type of local system. For single PCs connected to ADSL, firewall software running on the PC should be adequate.

Packages like BlackIce Defender, ZoneAlarm and Norton Personal Firewall monitor traffic into and out of the PC over the web, as well as prevent access based on a set of built-in and user-modifiable rules.

These prevent simple 'port scans', where malicious users test your IP address for vulnerable TCP/IP ports and services, and protect against Trojans like SubSeven. For networked PCs connected to ADSL, the Ethernet router itself will usually include a firewall, which you can configure through a web browser, that secures your machines from malicious attack.

Security might not seem serious, but every ADSL user looking at the event logs of ZoneAlarm or BlackIce Defender will be startled by the number of possible attacks recorded and blocked, which can run into dozens a day. With a permanent connection to the internet, you become an easy target.

Every ISP offers a range of hardware, but there's no need to restrict yourself to this. The ISP's connection software won't care what connection you make to the ADSL socket, so more experienced users might want to look around for better deals on USB ADSL modems and Ethernet routers.

Either way, with the microfilters, modem/router box and appropriate driver installed, an ISP contract and connection software running, along with security in place, your wires-only ADSL installation is complete.

What can you expect?

All ADSL connections are asymmetric, so the downlink rate to your PC is higher than the uplink rate to the internet, although the numbers depend on the services the ISP is offering.

The theoretical maximum downlink rate is 8Mbit/s, although the maximum currently available in the UK is 2Mbit/s and all uplink rates are currently restricted to 256Kbit/s.

For home users, the most popular choice is 512Kbit/s down, 256Kbit/s up. What this means depends on what you use the internet for.

Users who spend most of their time browsing websites or downloading files will find everything happening faster but there will still be glitches thanks to latency, the time taken for the page request message to be accepted and responded to by the remote site.

Perhaps more importantly, the always-on flat rate nature of ADSL means you don't have to worry about file sizes or long download times any more, as you'll be doing it at much higher speeds.

The wider bandwidth also makes it easier to use services like internet radio, but the promises of specialised broadband content have never materialised.

For business users, depending on the services you've paid for, extra benefits appear. If you have a static IP address and appropriate security, for example, you can connect to your ADSL-connected PC or network from anywhere in the world for file access or other services.

You might even be able to set up a virtual private network (VPN) linking your distributed offices securely and at speed, or run video conferencing to cut down on business travel.

However, none of these things are certain. The possibilities are there, but there could be practical limits.

What you can and can't do

For ISPs, offering ADSL connections to the general public produces potential headaches. For example, all connections from the user to the local exchange are at fixed data rates between 512Kbit/s and 2Mbit/s downlink, and 256Kbit/s uplink, but the connections from the exchange to the ISP backbone are limited.

This brings in the 'contention ratio' quoted in ISP literature, where the bandwidth available behind the exchange for a group of ADSL users is calculated on a realistic, not maximal, basis.

For instance, 2,000 users on the full downlink rate of 512Kbit/s would need 1,000Mbit/s of backbone bandwidth, which is uneconomic.

Instead, ISPs typically provide 20Mbit/s for 2,000 users at a contention ratio of 50:1. This works on the assumption that not all the users will want the maximum bandwidth all the time, that internet connections are 'bursty' by nature, and that most people won't notice any slowdown at this ratio.

For heavy business users, contention ratios of 20:1 are available at extra cost to guarantee higher speed throughput.

The same ratios apply to uplinks, but the reduced speed of this part of the asymmetric DSL connection adds further problems. For instance, you can't run a high-volume commercial web server over your ADSL connection, as this uses the asymmetry the wrong way round. If enough users did this, the contention ratios would clog up the system.

Non-commercial web servers with low traffic volumes are fine, as are low-volume FTP servers for file download and peer-to-peer servers for music files.

This might be frowned on for copyright reasons, but bandwidth and contention ratio concerns don't necessarily arise for the ISP, although some providers are experimenting with limiting bandwidth to these services.

Another limitation could be IP addressing. The basic home service offered by ISPs uses dynamic IP address allocation, so you're issued one from its pool of numbers when you connect and there's no guarantee you'll get the same one if you disconnect and reconnect.

This might not seem important, but disconnection does happen; the BT ADSL backbone has gone down at least once. For business users, remote connections to the local ADSL network depend on knowing what the IP address is.

If you have a private web server or VPN, the IP address is the method you use to connect to it. If that can change, then these services won't work reliably. This is why ISPs charge extra for fixed IP addresses.

There are similar limitations with a fixed IP address for your ADSL-connected PC or router. The shortage of IP addresses has brought about a technique called Network Address Translation (Nat), which means that not every device on a local network needs a unique IP address.

One ADSL IP address is issued by the ISP, then the router issues local IP addresses to all connected devices on the local area network (Lan). When a message goes out from a Lan PC to the internet over ADSL, its local IP address is replaced by the single address supplied by the ISP so, as far as the web is concerned, every PC on the Lan shares one IP address.

Microsoft is attempting to address this in Windows XP with its NAT Traversal feature, which applications can use to bypass these problems. However, NAT Traversal requires routers that support Universal Plug and Play, which are few in number to date.

There are other limitations. Some ISPs might restrict the TCP/IP ports you use to prevent running bandwidth-hungry services. You might also be discouraged from running an SMTP server to restrict spam email. And, of course, there are restrictions on distributing illegal material.

However, as long as the service isn't abused, ADSL users are pretty much free to do whatever is legally allowed.

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