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Christopher Spry

ADSL in the UK

On 1 November 2000, BT installed a 'Universal Serial Bus' (USB) 'Asymmetric Digital Subscriber Line' (ADSL) service for me through the Wimbledon exchange in South West London. As this was a new commercial service, starting in June 2000, I have collected information about USB ADSL, which may be of interest to others. It is based on my use of the BT 'Openworld Home 500' USB version of ADSL under 'Windows 2000 Professional'. In November 2003, I closed my 'Openworld' 500 account and started using a PlusNet '1-MB/sec, home installation, no modem' service, which is faster and offers a larger range of services than BT 'Openworld Home 500', especially excellent phone support.

Note that much of the specific information here has not been updated since 2001, but some of the general points are still valid. It was based on my experience of setting up and using ADSL in the early days of broadband service provision in the UK. Please send me corrections and suggestions for updates.


1. The basics of ADSL

ADSL is the latest communications technology to enable computers to connect to each other over Internet using a standard copper telephone line. It is a replacement for dialup modems and ISDN. The ADSL 'signal' is carried by two ADSL routers, which look like modems.  ADSL routers send IP packets through the copper wire that links your phone to the local telephone exchange, which has to be less than about 5 km away, to ensure there is no significant signal loss. The line is tested to ensure that it will support ADSL before it is installed. One of the ADSL routers is provided in your premises and the other is in the local telephone exchange. A 'splitter', or 'filter', at each end of the line, separates voice and ADSL signals, so that phone calls can be made at the same time as the ADSL link is being used. 

The main advantage of ADSL is that the connection appears to be always 'on', so there is no wait to get connected to Internet, it is much faster than ISDN (about 50 KB/sec) and there are no call charges: the charges include an installation charge, then a fixed fee for a set period: month, quarter or year.

There are two types of ADSL router. One type has an ethernet (RJ45) connector on it, which is used by more expensive services, because it is designed so that several computers on a local network can use the service directly through the router. The other type of router has a USB connector, which provides the cheaper (domestic) services. The USB version of the router is designed to be used by just one computer, although several computers on a local network can be set up to use the service via the computer attached to the router.

Routers at the end of each line must be using the same DSLAM protocol, which will be either 'PPPoE (naturally ethernet)' or 'PPPoA (ATM)'. BT's 'Home 500' service uses PPPoA. Each type of modem can use either protocol. The service provider decides which one to use. It makes no difference to the user which protocol is run.

  • ADSL routers, that have RJ45 connections, are often provided with a 'static' or fixed and registered IP address. In this way, the local network can be an Internet web server and provide e-mail, ftp and other functions to and from other computers on Internet. Clearly, this type of network must have security, such as a firewall, in place. Other ADSL connections using RJ45 connectors, where higher security is needed, are just provided with a single, real, RIPE registered, IP address and the other computers attached to the ADSL router are given private network IP addresses in the reserved range '10.x.x.x', which is not visible from other networks. The reserved IP addresses are either set manually on each PC, or via DHCP. The PCs use these IP addresses to communicate with each other on the local network and with the ADSL router, using a protocol called 'network address translation' (NAT). Perhaps the main benefit of ' NAT' connections is that an external hacker can not connect directly to PCs on the private network and cause problems. This is because the local computers cannot be accessed directly by computers elsewhere on Internet, which can only 'see' the IP address of the ADSL router. But note that NAT is not resilient to all types of attack, so extra security is still recommended. 
  • ADSL routers, that have USB connections, are often provided with a 'dynamic' (variable) IP addresses. This type of connection is the cheapest to setup and run. More customers are allocated to each segment of the network than other the first type of ADSL connection described above. The 'USB' router can only connect to a USB port on a single computer. This computer must be running Windows 98Millennium (ME)Windows 2000 Professional, Windows 2000 Server orWindows XP, because other Windows operating systems do not support the USB port. Computers running Linux can be setup to use ADSL routers - see below. Other computers on a local network can run any of the Windows operating systems, as they use the service via the computer attached to the USB router. The 'USB' version of the ADSL router is not 'NAT-enabled' and no ports are blocked. 

In practice, there is little difference between RJ45 and USB ADSL connections, because networked computers can also use the ADSL USB resource on the connected PC, if they run connection software that include Windows 'Internet Connection Sharing'. The main difference is that connections from Internet to the USB-connected computers are usually designed to run slower and they are not designed to run a web and other Internet services from the local computer. They may have slower transmission speeds at peak times, because more people share a line, i.e. have a higher 'contention ratio'. Some potential uses of ADSL, such as web hosting, are not allowed in some service contracts for USB ADSL connections, so it is worth checking details before deciding which service provider and which service to install. If you need them, upgrade to services using routers with RJ45 connectors and fixed IP addresses.

Peter Jackson has given further details of how ADSL works, in his article 'What is ADSL?', in 'PC Magazine' July 2002 page 74.

"We take a closer look at the latest technological development to come out of the Digital Subscriber Line family.

ADSL is one of a family of Digital Subscriber Line (DSL) technologies generally grouped under the xDSL name. All of these use the full bandwidth of the copper pair wiring from a local exchange to your location to transmit much more data per second than a conventional dial-up modem link. ADSL is the asymmetric version of DSL, where the downlink speed from the exchange is greater than the uplink speed, although symmetric (SDSL), high-speed (HDSL) and other variants are in development and use.

ADSL splits the 1.1 MHz maximum bandwidth of a copper wire connection into 4KHz channels and uses only the bottom 4KHz channel for normal voice and fax data. The other 256 available channels are used for parallel digital communication, with—for a typical home connection—one frequency band of 64 channels reserved for uplink data and a higher band of 128 channels reserved for downlink data. It should be clear that if the uplink rate is kept the same at 64 channels, the maximum downlink rate uses 192 4KHz channels, giving the 8Mbit/s maximum download rate for ADSL. At present, 2MbiVs is the maximum being made available.

In effect, ADSL takes a serial string of digital data and turns it into a parallel string, thus increasing data throughput. The encoding and decoding is done at the exchange and at the user site, as is the case for conventional modem dial-up.

The modulation used for ADSL is Discrete Multitone (DMT), now universally adopted as the standard. An earlier system, called Carrierless Amplitude Phase (CAP), could use all the band- width above 4KHz as a single transmission channel and had the advantage of being closely related to the Quadrature Amplitude Modulation (QAM) technique used by high-speed modems at rates above 9,600biVs. However, DMT offers more flexibility—although the costs are higher for silicon encoders and decoders

At the user end, the ADSL modem or router collects high-frequency digital data and assembles it for transmission to the PC or network. At the exchange end, a Digital Subscriber Line Access Multiplexer connects the ADSL user to the wider Internet, combining multiple ADSL lines into a single data connection for the broader Asynchronous Transfer Mode (ATM) network behind.

Rate Adaptive DSL (RADSL) is now the only variant installed in the UK. This has broader distance tolerances between exchange and user location—5.5km against 3.5km—and looser noise restrictions, with a top limit of 55dB. RADSL manages this by varying the speed of the less-critical uplink spectrum if required, stepping down from the rated 256Kbit/s to 64KbiVs in increments of 32KbiVs as line quality or noise dictates. This means most home users won't notice any difference, as the downlink channels are unchanged, although those playing online games or depending on uplink rates for remote access might find the link slowing under certain conditions.

The microfilters required for wire only ADSL divide the frequency channels. One filter separates the bottom 4kHz of the spectrum for conventional voice calls, faxes, modems and any other equipment that previously used the old audio system. The other separates off everything from 4kHz to 1.1 MHz for use by the ADSL digital channels. Microfilters split the signal in a standard telephone socket to allow voice calls and data simultaneously."

See also:

2. Requirements for the USB ADSL services 

Note that this section refers to the use of the Alcatel USB router, which BT supply to connect the computer to the ADSL socket. An alternative is to use a separate router, see below, which is connected to the ADSL socket and provides network ports (RJ45) for networked computers.

3. ADSL providers in the U.K.

There is a list of ADSL providers at 'ISP Review'. A comparative table of over 39 ADSL providers is available from NetConnex Ltd. All of them use the ADSL hardware provided by BT's division called 'BTIgnite' in BT exchanges. All ADSL Internet Service Providers, including BTOpenworld, are supposed to be treated equally by 'BTIgnite', when setting up ADSL services for customers. On 13 December 2000 Telewest, NTL, Global Crossing, Worldcom and KPNQwest scrapping their earlier plans to provide DSL services, in view of the high cost of setting up the networks to support it.

NTL broadband @ £17.99/month for 150K connections is available from May 2003, for UK cable users.

Late delivery by BT, who do most of the installation work, is a problem for some ISPs, so confirm planned installation dates before making a firm commitment.

BT has developed a video on demand (VOD) product called 'Videostream' which uses ADSL to transmit videos to television sets.Videonetworks use this product to provide their ADSL services and it is sold under the brand name of 'HomeChoice'. Part of the ADSL bandwidth is available for computer users to access Internet. The service was designed to be an alternative to Sky Digital and other digital video and TV service providers. I have not used the service, but I have read that the TV picture quality is, unfortunately, visibly lower than other digital TV services. The main problem for computer users appears to be that the allocation of bandwidth on the HomeChoice ADSL line between the Internet service and the TV service is fixed. This means that you may only get speeds of up to about 10 KB/s to Internet with HomeChoice, whereas dedicated ADSL connections regularly provide 50 KB/s.

4. Installing the ADSL USB driver on the host PC

BT usually provide a 'Welcome Pack' with information about the service, with your account number, 'logon gateway username' and a 'logon password' (PIN number), before an engineer is sent to install the connection box and USB router at your site. If you do not receive it, phone BT's Order Management 0800-917 9189 several days before the engineer is booked to visit, and ask them to send it. The 'Welcome Pack'  should contain a CD containing the latest approved Alcatel USB ADSL driver software for the router. Alternatively, the engineer may bring the CD with him. You can download from 'BT Openworld' and install the latest BT-approved Alcatel USB router driver software (Alcatel USB DSL driver version 1.4, May 2002). Note that, if you have the early and faulty 'BT version ab04' Alcatel driver, you should replace it with the latest driver. The newer Alcatel Speed Touch USB driver still under test isversion 1.60 beta (May 2002). This driver should only be used when other drivers are not working.

The engineer is not allowed by BT to install the Alcatel USB ADSL driver software on your own computer or check that your computer is able to use the service. His function is simply to wire the router to the splitter box in your premises, attach it to the router, switch it on and check that his portable computer is able to view a BT diagnostic web page using the router. 

 It is highly recommended that you install the Alcatel USB ADSL driver software on your own computer before the engineer comes or while he is working on your phone line. If you do this, you will be able to test the line before he leaves. The router should not be connected, while the driver is being installed. To install the driver from the CD, insert the CD into the CD-ROM drive on your computer and follow the instructions on-screen. Otherwise, use the downloaded driver to install the software. Once the software is installed, reboot the computer. Then attach the USB router and it will be 'recognized' automatically and installed as a device, which is visible in 'Device Manager' under 'Modems'.

If you are using Windows XP, use the 1.3 version drivers included on the CD-ROM supplied with the Alcatel USB router. Do not use the later version 1.4 drivers, as they may cause problems under Windows XP. To install the Alcatel router under Windows XP, do not preload the drivers but simply plug the modem in and when the 'Found new hardware' wizard starts, let it install automatically the drivers present on the supplied CD-ROM.

5. The work done by the BT engineer at your premises

ADSL connections are organized by BT's 'ADSL provisioning', who notify an 'Engineers Manager' to send an engineer to install the service. The engineer will take 20 minutes or more to install the splitter box and router at your site. He will extend your incoming phone line close to where you will be using the computer and attach an ADSL 'splitter' box to the wall. This box has two sockets: One is for a standard telephone handset. The other socket has a 2-m cable that connects the splitter socket to the Alcatel ADSL modem, which sits beside the computer. The USB router does not require an electrical outlet for power which is taken from the computer's USB port. 

When the router is powered up, green lights at the front confirm that the router is switched on and can 'sync' with the external line, but there are no lights to show whether it has been configured properly. A blinking green light shows that a connection is being negotiated. A persistent blinking green light indicates a problem in the connection between the router and the exchange.

The engineer will use a BT portable computer to connect to the router and check that the ADSL line is working. He logs in to a reserved ADSL BT site as startup_user@startup_domain with no password. If this fails, he may phone BT's Broadband Operations Unit (BOU) and ask them to check that they can 'see' your router and, if necessary, download configuration data into the router. He will persist until he can connect his portable computer to the BT web site. However, as this site is not on Internet, his connection is no guarantee that Internet services will work for you. He cannot test Internet connections through the DSL line, as his portable computer is configured to only access the BT site.  As the engineer is not able to check that the ADSL service is working properly with your computer, you would be wise not let him go until you have checked the service yourself.

It is highly recommended that you check that the ADSL service works, before the engineer leaves your premises. Otherwise you may be faced with many frustrating phone calls to BT. These are seldom answered in less than 30 minutes and you may only be able to talk to an operator who will relay your messages. Users are reporting that non-functioning connection can take days or weeks to fix. BT do not guarantee that the line will function from any specific date. 

6. Checking that the router and service are set up correctly before the engineer leaves

Here are some of the things that you can do to test the service quickly, while the engineer is tidying up or having a mug of tea.: 

First, connect the cable from the router to the USB port on your computer after installing the USB driver. It will install automatically.

Then setup a 'Network and Dial-up Connection' to your Internet Service Provider, which was 'BT Openworld' in my case. Use the 'USB router' as the device, put a space in the phone number box and the TCP/IP settings must be set to obtain an 'IP address automatically' and 'DNS servers automatically'. (If you have a router with an RJ45 connector, which provides a static IP address, the 'Network and Dial-up Connection' to your Internet Service Provider will have to show the IP address for your router. BTOpenworld DNS servers have IP addresses to 104). 'Dial' using this connection and enter your 'logon gateway username' and 'logon password' there and hope that you will connect to the ADSL service. The 'logon gateway username' will be of the form ofemail/username@hgx.btinternet.com (for example jbloggs@hg3.btinternet.com). Both are usually provided in the 'Welcome Pack'. I f you do not know what they are, or you suspect that they are different from what you were sent, phone BT 0845-600 7020 to ask for them. If you see the error message 'Error 650. Unable to contact remote server', the service is not connecting in the exchange. If you suspect that this is because BT's gateway computers are malfunctioning, attempt to deal with this as described below under 'Home Gateway'. If this does not work, request the ADSL engineer to telephone BOU to check that the router is visible at their end and if necessary to configure it correctly. Persist until the router is shown to be functioning properly and you can connect and use Internet. Some users have reported that there are malfunctioning routers, so it would be sensible to ask the engineer to try another router, if you are unable to make a connection. If you suspect that the problem is with your username/password entry, try to log in with the 'test' username: startup_user@startup_domain with no password, and see if that works. 

If you have a router with an RJ45 connector, which provides a static IP address, try to 'ping' this address from the computer. If this fails, the router is not working and it should be replaced. Now ping the NAT address to see if it is visible on the local network. 

7. Setting up an Internet Service Provider (ISP)

The organization that contracts to provide your ADSL service is your ISP. They will provide details of their services. It is not always necessary to install their software that alters your web browser in a way that shows that you are using their service. You will be using their services as soon as your computer is connected to ADSL, because your connection is routed automatically to their servers. There will be email, Usenet and other resources which are specific for each ISP provider. In the case of BT Openworld, you only need to install the Alcatel modem driver, as described above, and have an ADSL connection, to use 'Openworld'. The 'Openworld' POP3 and SMTP servers are both called 'mail.btinternet.com' and the Usenet news server is 'news.btinternet.com'.  Business users with the RJ45 modem and 'OpenWorld', will be connected to the 'BTClick' email, news servers and web servers, whereas home users with the USB modem who install 'OpenWorld', will be given access to the 'BTInternet' servers which provide the same services as 'BTClick'. Users can have up to 10 email accounts. Users' web site have the URL http://www.username.btinternet.co.uk/.  A telephone dialup account is automatically made available at 0845-756 0000 for users who have a BTOpenworld account. Login using 'username@btinternet.com' and password.

8. Connecting to the ADSL service at startup or login

If you wish to connect automatically to ADSL each time that you startup your computer or login, you can either:

  • Place a shortcut to a web page in the 'Startup' folder and set the default 'Dial-up Networking' setting to 'connect automatically'.
  • Under 'Windows 2000 Professional' you can start up the connection on a command line by running 'rasdial connection_name username password'. Then you can store this in a .cmd file and put a shortcut to it in your startup group.
  • It is possible to make this 'rasdial' command a 'service', to load automatically when the computer boots.
  • In Windows 2000, set rasdial.exe to start the connection as a Group Policy at login, as recommended by an anonymous correspondent: 1. Start Microsoft Management Console (MMC) by clicking Start, clicking Run then typing 'mmc'. 2. On the Console menu, click Add/Remove Snap-in. 3. Click Add, click Group Policy, and then click Add. 4. Click the appropriate Group Policy Object (the default selection is the local computer). Note that you can click 'Browse' to select a different Group Policy Object. 5. Click Finish, click Close then click OK. 6. In the Group Policy Management console, locate the following folder: 'User Configuration\Windows Settings\Scripts (Logon/Logoff)'. Note that you can substitute the Computer Configuration folder for the User Configuration folder. 7. Double-click the Logon script object. Click Add, click Browse then click the c:\winnt\system32\rasdial.exe. 8. After you select rasdial.exe, click Open, and then click OK. 9. Add <connection name> <username> <password> as the options. 10.Click OK, and then close the Group Policy Management console.

In Windows NT and Windows 2000, you can logout as a user, but retain your ADSL connection, as explained at Microsoft:
"082 » Keep your RAS connection when you logoff Windows NT/2000, edit: HKEY_LOCAL_MACHINE\Software\Microsoft\WindowsNT\CurrentVersion\Winlogon
and add the value KeepRasConnections as a type REG_SZ. Set it to 1"

9. Known problems with UK ADSL

Note that, if a web page author wishes a page to have a lifetime of five minutes before a transparent cache checks for new content, then the http header for the page should contain the following control: 'Cache-Control: max-age=300'. Alternatively, if the author would like their web pages not to be cached by a transparent cache at all, the http header should contain the following control: 'Cache-Control: no-cache'.

If you are using a router and 'microfilters' (splitters), ensure that you do not use a phone that is connected to the ADSL line without a splitter. If you do, the ADSL connection may fail and you will have to reboot the router to reconnect to ADSL. The phone line will also be noisy and unusable. 

10. After setting up an ADSL connection

11. Dynamic and fixed IP addresses

The cheaper 'Home' or 'USB' ADSL services provide a 'dynamic' IP address, which may alter each time that a connection is made to the ADSL service. In April 2001, BT altered the way that they configured DHCP, so that a user would probably be given the same IP address as before, if the interval before reconnecting was not more than about 20 minutes and if there were not many requests for IP addresses at the same time.. 

12. Security

13. Networking other local computers to use an ADSL connection: ICS

I have a guide on how to setup  Microsoft's 'Internet Connection Sharing' (ICS) to enable other computers on a local network to use a USB ADSL connection. Networked (client) computers will obtain their network IP addresses from the (host) computer which is connected directly to the USB ADSL router. Note that use of ICS on BT's USB routers may be contrary to their 'Terms and Conditions' and ICS is not supported by BT, so check before installing it. Business users of the RJ45 ADSL modems simply need to add the network addresses provided for them for each computer on their network, to connect to local computers and Internet. Advanced network installations that need to hide the local network from Internet users, can use 'Network Address Translation' (NAT) routers which link to the RJ45 ADSL modem.

14. Networking  a local computer through its ADSL connection to a remote computer: VPN

Networking to distant computers through ADSL is usually best done using Virtual Private Network (VPN) software. VPN runs on the local client computer, which can then tunnelling across ADSL to a distant computer, which is configured to run VPN in host mode. All data is encrypted between the two networked computers. Many VPN protocols can be set up to work well across a Home500 BTOpenworld connection. Computers running  'Windows 2000 Professional' and 'Windows 2000 Server' can be VPN hosts and/or VPN clients. See a Microsoft TechNet article and the ' Help' section of ' Windows 2000' for details. Windows 2000 users can set it up easily. Click 'Start | Settings | Network and Dialup Connection | Make New Connection | (do not select any options) Next ' and select either 'Connect to a private network through the internet' to create the VPN client, or 'Accept incoming connections' to create the VPN host. The connection will persist as long as the IP address of either computer does not change.

15. Support and what to do if the service stops working

If the ADSL connection fails but the router lights are both green:

If the lights on the router are not green but show or flash orange or red:

Complaints about BT's Openworld service should be sent by email to complaints@btopenworld.com or given by phone 0845-6007020 or 0845-6007030. Each complaint is allocated an adviser.

16. 'Business Plus' services with a fixed IP address

Eugenio Mastroviti has provided me with his experience of the 'business' service provided by BT.

17. Alternative routers to the standard Alcatel USB router

Routers can be bought to replace the Alcatel USB modem, which is usually provided for ADSL connections and is owned by the service provider. The main advantage of replacement routers, is that they maintain a connection to Internet without needing a computer connection and they can provide NAT and other secure functions for a local network using RJ45 connectors. Note that some ADSL service provider agreements specify that their routers must be used, but this may alter, now that 'better' alternatives to the Alcatel USB router have become available. The list below is only some of the available hardware.

 I have no experience of using any of the following:

18. Planned improvements and updates of BT's ADSL services

RADSL In June 2001, BT in conjunction with the ADSL supplier BTIgnite, ran a 'limited volume, invitation only' trial of an 'extended reach' ADSL product  (RADSL), which uses a USB rate-adaptive modem to increase the ADSL 'footprint' around an enabled exchange to about 5.5kms (or a 55dB line loss) in return for a slightly reduced upload speed. This varied from 250k to 64k, download speeds remained the same. The public service was made available from July 2001 in BT Wholesale IPStream 500 (USB), IPStream S500 (Ethernet) and Home/Office 500 (wires only).

BT plan to trial a 'Wireless Hub' later in 2001. This will allow users to connect, for example, a Hi-Fi system and TV to a broadband connection, which will provide multi-channel digital internet radio around the house and other wireless networked functions.

G.SDSL is being tested in Europe as a possible successor for ADSL. It transmits at up to 2.3 mbps and can link to sites over 3 miles from an exchange using repeaters.

Go to the 'home page'

Go to the 'computer index page'

Partial update 25/08/2020