What is ADSL?
ADSL, or Asymmetric Digital Subscriber Line technology is a means of
transmitting digital information at high bandwidth down existing copper
telephone cable. It is permanently 'switched on', unlike normal dial up
access and is asymmetric in that it uses most of the available bandwidth
downstream. This makes it particularly suitable for applications where
customers expect to receive more data than they transmit such as for Web
browsing, use of corporate intranets, and reception of digital
audio-visual material. The technology also supports analogue connection on
the same line, which enables voice or fax calls to be made simultaneously.
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What are the key benefits of ADSL
for me?
Firstly, the Speed. ADSL provides high-speed digital access - e.g.
potentially 10 to 40 times faster than today's typical modems.
It’s Always On. You
will no longer have to waste valuable time obtaining a dial-up connection
to your Internet Service Provider or Corporate Intranet
It’s Flexible. It does
not affect the normal telephone, so you can make and receive telephone
calls or faxes whilst you’re online.
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What are the key benefits of ADSL
based services for Business?
ADSL based services will allow SME's and Corporates to:
* Take full advantage of
broadband capabilities.
* Offer innovative services to your end user base.
* Extend the reach of your Intranet to encompass your remote teleworkers
and satellite offices.
* Manage and predict your costs with the flat rate charging scheme
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How fast is it?
Typical rates for ADSL are shown in the table below.
Downstream speed Upstream speed
Up to 500 kbit/s Up to 250 kbit/s
Up to 1 mbit/s Up to 250 kbit/s
Up to 2 mbit/s Up to 250 kbit/s
This is between 10 to 40 times faster than today's typical modems.
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Who are our ADSL based services
aimed at?
Our services are aimed at a wide range of consumers. Corporate business
users will be able to provide their teleworkers or satellite offices with
remote access to the corporate network, whilst home users will be able to
take advantage of the incredible download speeds to view digital media on
the Web, such as movies, music and similar bandwidth hungry applications.
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What can ADSL be used for?
ADSL's higher potential bandwidth has the potential to enhance access to
existing services and applications and stimulate the development of new
ones:
Internet access
The access speeds available with ADSL available make it practical for web
sites to carry more multi-media rich information such as embedded video
clips, animations and good quality audio - significantly enhancing the
online experience
Intranet access
Fast access to the Intranet makes teleworking an attractive option - which
in turn can bring benefits to both the organisation and the individual
TV based services
ADSL can be used to deliver interactive applications to the TV, such as
real time video and audio, home shopping and home banking
Future services
ADSL will be the catalyst for a wealth of new information, education and
entertainment services
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When will I be able to have ADSL
installed?
This is dependent upon BT's roll-out schedule for ADSL serviceability of
your geographical area.
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What
if my modem/router wont connect?
1) Check that the microfilters are plugged into the phone line, and all
cables are in correctly.
2) if you have a PBX on
the same Line as the ADSL, the service will not work, please contact us
for advice.
3) If none of the above
please call us.
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How have BT chosen which exchanges
get ADSL enabled first?
BT have chosen a number of criteria to establish which exchanges should be
provisioned for ADSL first. These included demand for bandwidth and where
the early adopters of these services are most likely to be located.
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What do I need in order to be ADSL
serviceable?
There are a number of factors that will determine whether you will be able
to take advantage of ADSL.
These include:
That you are a BT subscriber. You must have a valid contract for the use
of a BT analogue direct exchange line forming part of the BT network over
which the ADSL service will be provided. Note that if you rent your
premises, you must have a valid contract for a BT or Calls & Access
provided PSTN line. It is not suitable that the contract be held with your
landlord rather than yourself.
Whether BT has upgraded your telephone exchange to ADSL technology, and
whether you are located within a specified distance from the exchange.
That you are aware of the installation procedure and requirements in terms
of equipment as well as location.
That there are no incompatible services on your PSTN line.
That you have sufficient mains power sockets for the BT NTE (Network
Terminating Equipment)
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Are there any Service Constraints
I should be aware of?
The transmission performance of some local loops will mean that it is
technically impractical to deliver ADSL service to all end users with a
particular serviceable area. BT reserves the right to refuse ADSL
installation even if you are situated in a serviceable area.
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What services on my line are
incompatible with ADSL?
ADSL service is not compatible with these BT services:
Subscriber private metering
30k loop
Private circuits
Red ABC
RedCare
Meterpulse facility
PBX lines
It is only possible to provide a single broadband service over a single BT
or Calls & Access PSTN exchange line.
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How does ADSL work?
ADSL operates over a normal telephone line. This means that there is no
need to dig up any roads to replace cable and install it. The ADSL signal
is carried by two ADSL modems - one in the end user's premises and one in
the local exchange. These ADSL modems are designed to exploit the physical
transmission capabilities of the copper line to the maximum extent. The
resultant ‘broadband’ medium is used to achieve much higher data rates
than were previously possible. Two 'splitters' (filters), one in your
premises and one in the BT exchange, separate the telephony signal from
the ADSL signal. This means that telephone calls can be made at the same
time that data is being sent or received (i.e. a customer can surf the
Internet and still make telephone calls concurrently).
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Is my fax compatible with an ADSL
set-up?
It is not guaranteed that your existing fax machine will work after you
have installed ADSL. Please check with the fax machine manufacturer/vendor
to check ADSL compatibility.
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Will ADSL affect my normal
telephone connection?
You may notice a slight change to how your telephone sounds after you have
ADSL installed. This is normal for ADSL lines and is not a fault. Any
standard modems operating on your PSTN line (standard telephone, not the
ADSL line) may operate at a reduced speed after ADSL installation.
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Will telephone calls be charged
separately?
Yes. Normal telephone rental and call charges will still apply.
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Can customers keep an existing
telephone number?
Existing BT PSTN numbers will be unaffected; most end users will be able
to keep their existing telephone number.
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Who is responsible for billing?
You be billed by us for your ADSL service. If you have any queries about
your ADSL account you should contact us and not BT.
The price, billing and payment for your standard BT telephony service will
remain unchanged and BT’s responsibility.
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Will all BT Select services be
supported?
Yes, all Select Services can be supported on the PSTN line, including Call
Waiting, Call Return and Caller Display.
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Will ADSL affect my burglar alarm
or security system?
Installation of ADSL may adversely affect security or burglar alarm
systems that use your PSTN telephone line and fail to operate correctly.
You should check with your suppliers for compatibility of your system
before arranging for ADSL installation.
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Which IP services are compatible
with ADSL?
The service supports most protocols including Telnet, SMTP, HTTP, FTP,
TFTP, VDO, RealAudio, Cu-SeeMe, QUAKE (2.8.0). ADSL will also support
instant messaging and communication programs such as NetMeeting, ICQ or
Microsoft Messenger. Some of the advanced functions of these programs,
such as video conferencing or file sharing, will not operate behind a
firewall or Network Address Translation (NAT) without some technical
configuration, or possibly not at all. If you have any questions, consult
the user Help for the specific program.
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What computer equipment do I need?
The equipment required and minimum specification of PC depends upon which
installation you are having, USB or Ethernet version.
For the ADSL Home and ADSL NetStart USB installation, you will need the
following:
PC with the
minimum specification of:
Windows 98 or Windows 2000 operating system
USB port (if you are not sure about this, please see your supplier. The
ADSL modem uses USB to connect to your PC).
4-speed CD ROM drive
200Mhz Pentium or above
32 Mb RAM or higher
Video card/display capable of 800x600, 256 colours
SVGA monitor
16 bit sound card
150 MB free hard drive space
For the Ethernet multi-user modem/router installation, you will need the
following:
PC with the minimum specification of:
Network Interface Card (10BaseT Ethernet port)
TCP/IP communications stack
Netscape 4 or IE 4 or above must be loaded onto at least one of the PCs
connected to the service. The browser must be JavaScript enabled.
Other specifications will depend upon the applications you want to use
with your ADSL service and the operating system you are using. For basic
Internet browsing this should be at least:
Pentium 166Mhz, MMX or above
32Mb RAM or above
150MB available hard disk space
SVGA or higher rated monitor
Video card/display capable of 800x600, 256 colours
Windows 3.11, Win 95 or Win 98 - or, Windows NT or Windows 2000
4-speed CD ROM player
16 bit sound card
Mouse or other pointing device
If you wish to use Apple MacIntosh on your network, the machine should
conform to the following specification:
Or a Apple Macintosh with the following is recommended:
PowerPC 601 or equivalent
32MB System Memory
2-speed CD ROM player
Video driver and display capable of 800 x 600, 256 colours
100MB free space on hard drive
OS8.1 or higher
Open Transport 1.3 Networking Software
10baseT Network Adapter with an RJ45 connector
You will also need appropriate lengths of Ethernet cable to connect your
PCs to the ADSL router/hub. Note that a length of 100 meters must not be
exceeded between the PC and hub.
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Can you tell me more about the
line testing and validation?
After initial ordering, BT engineers will make preliminary tests on your
line to make sure that you are ADSL serviceable. If the tests conducted on
your line show that BT are unable to install ADSL at your location, you
will be told the reason for this. Some examples of situations may be line
quality, distance from the exchange, incorrect information being supplied
upon application etc.
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What is the minimum contract
period?
The minimum contract period is twelve months. Your contract is with us and you
should contact us rather than BT if you have any queries. If you want a NO
CONTACT Service you can pay an activation fee of £65inc vat, this will
provide you with a no contract service, but require a months notice for
cancellation.
In the event that you do
want to cancel your 12 month contract service early, you will be required
to pay the remaining month/s rental.
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If I move premises what will
happen to my ADSL connection?
Your contract with BT and ourselves is for your specific location and
subject to a minimum period. This minimum subscription period would remain
payable if you move location whether or not your new location is ADSL
serviceable. If you require ADSL at the new premises then you should make
arrangements for a new installation and your old contract will be replaced
by a new one.
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Who do I report faults to?
You should report faults to us and not BT in the first instance. The only
exception to this is if the fault affects only telephony services.
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Is it dangerous to be permanently
attached to the Internet?
Any computer that is connected using ADSL to the Internet is exposed to
the same security risks as a dial-up user, however since ADSL users are
typically connected to the network for longer periods of time (always on)
this risk is potentially that much greater. You should be aware of the
potential of hacking attacks and the precautions that you should take.
Please read our security section.
Some examples of good security practice are:
Turn off your PCs when not in use.
Turn off Windows File and Printer Sharing
Install a virus checking software product and ensure that it is maintained
to the latest version.
You should provide a Firewall in the case of a sensitive installation.
You should provide encryption of data transmission for sensitive data.
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How do I set up my USB modem?
The details, together with diagrams, explaining how you should set up your
USB modem with your PC are available here.
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How do I set up my Ethernet
equipment?
The details, together with diagrams, explaining how you should set up your
Ethernet equipment with your local area network or single PC are available
in here.
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Can you explain how the contention
ratios work?
The USB modem and the Ethernet router solutions have different contention
ratios set up by BT, with these values set at 50:1 and 20:1 respectively.
This means that for a Home user with a USB modem, the BT connection at the
exchange is shared with another 50 users. Whilst some degree of
performance loss will be experienced during peak periods, it is generally
accepted that few people will be downloading or uploading data all at the
exact same time. For the business user it makes sense to go for the 20:1
business version, which will not be subject to so much slowdown at peak
periods. The two systems will be able to co-exist on the same 'local loop'
due to BT's network tunnelling protocols, each connection being given its
own port on the exchange terminating equipment (DSLAM).
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Do ADSL services work with non-BT
PSTN lines?
Currently the Broadband services are only available over a BT PSTN line. A
non-BT PSTN variant is being investigated.
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What standard does BT's ADSL modem
adhere to?
Various forms of ADSL signal modulation are possible but the two more
prevalent are: Discrete Multi-Tone (DMT), and Carrierless Amplitude
modulation Phase modulation (CAP). DMT uses interleaving to achieve good
error performance and has become the international standard.
BT evaluated both DMT and CAP modems during their extensive trials
throughout 1998 and 1999. However, their commercial ADSL based services
will use DMT. Alcatel and Fujitsu will supply these modems.
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Will BT be blocking any TCP port
numbers?
There has been some speculation in the press regarding the supposed
prospect of port blocking on the ADSL service. The huge popularity of
distributed networking programs such as Napster, Gnutella and iMesh has
led to fears of excessive bandwidth consumption. BT have stated that they
have no current plans to restrict bandwidth use or block particular ports,
although they may review this in the future if the service is adversely
affected by flagrant bandwidth abuse.
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What about other technologies?
What impact will UMTS have on ADSL?
Universal Mobile Telecoms Service - UMTS is the called the 3rd generation
mobile service. It is a mobile network whereas ADSL runs over a fixed
network. So, whilst UMTS will deliver broadband access too, the two
technologies are more likely to be complementary rather than head-on
competitors.
What is DSL Lite technology compared to ADSL?
DSL Lite/G.Lite is a lower speed, splitterless version of ADSL. It is
designed to offer around 1Mbps of capacity downstream, and 120kbps
upstream. Because there is no Splitter, it is easier to install but does
mean that the end user may experience significant interference between the
telephony and ADSL services when they are used at the same time.
BT's ADSL based services are based on the full ADSL standard, rather than
DSL Lite. BT is involved in the evolution of the standard for DSL Lite but
has no immediate plans to launch services based on it.
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Disclaimer:
Please note that although we endeavour to make sure that the information
included in this FAQ is up-to-date and accurate we cannot guarantee that
it is exhaustive, nor that changes won’t be made at any time without
prior notice.
ADSL Glossary of terms
ADSL –
asymmetric digital subscriber line
BROADBAND –
the technology of using the whole available bandwidth of the transmission
medium, in this case, copper telephone cable.
CONTENTION –
refers to the number of people who share the same local loop as yourself.
This means that the higher the contention rate, the slower the ADSL
network will become at peak periods. This is one reason why we regard the
Business ADSL variant as being the superior product because of its low
contention ratio of 20:1
CROSSOVER CABLE
– type of Ethernet cable
required to connect a PCs NIC directly to a router rather than a hub. This was
required during BT’s ADSL trials but is no longer required because the NTE
equipment (for the Ethernet variant) now has a built-in hub.
DHCP - Dynamic Host Configuration
Protocol. A process by which a machine assigns a single IP address to a PC
on a network. This IP address is taken from a 'pool' of addresses. The PC
would be set up to receive its IP address 'dynamically' via its networking
settings. This system allows easy administration of a network since
individual addresses are not 'tied' to a particular machine. Together with
the concept of a 'lease' whereby a time is specified for the duration of
that IP address, it becomes possible to administer a network where there
are more machines than available IPs in the pool.
DSLAM –
Digital Subscriber Loop Access Multiplexer. Located at the BT exchanges,
these are what your ADSL modem connects to.
ETHERNET –
the technology commonly used to network PCs (also referred to as 10BaseT
or 100BaseT)
IP - Internet Protocol. All machines on
a single network require a unique IP address in order to communicate with
one another. An IP address is divided into a network part, which must be
the same on any one network, and a host portion, which must differ.
LOCAL LOOP –
refers to the telephone network between your location and the nearest BT
exchange.
NAT - Network Address Translation. The
name given to the process whereby one IP (Internet Protocol) address is
mapped (or translated) to another. This generally occurs when a globally
valid IP address is mapped to an IP on a private (internal) network. The
benefits of this are several. Firstly it becomes possible to connect many
machines to the Internet with only a single Static IP address. It also
'hides' the actual addresses of the internal machines, since to the
outside world, all the machines share the same IP address - the network
looks like a single machine.
NIC –
Network Interface Card (Ethernet card, 10BaseT card) that is installed in
your PC in order to connect to a local area network. A PC expansion card
that allows a PC to communicate with an Ethernet network via appropriate
cabling.
NTE
–
Network Terminating Equipment – the BT equipment installed at you
location. Refers to the USB modem in the case of a single USB installation
or combined modem/router/hub in the case of the Ethernet installation.
PSTN –
Public Switched Telephone Network. The telephone network we use for
telephony services.
SPLITTER - device that splits the
available bandwidth of the copper cable into two or more sections, on for
analogue voice transmission, the other for digital data communication.
USB –
Universal Serial Bus - Universal Serial Bus technology means that your
computer will be able to connect to the very high speeds of ADSL without
slowing down the data (USB can potentially support speeds of
12megabits/per second).
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