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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 150 kbit/s Up to 250 kbit/s
Up to 250 kbit/s Up to 250 kbit/s
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 3 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?
CommRich are dependent upon BT's roll-out schedule for ADSL serviceability of
your geographical area.
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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 will make payment arrangements with CommRich and be billed by us for your
ADSL service. If you have any queries about your ADSL account you should contact
CommRich 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. Some ADSL
modems use the USB port 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 three months. Your contract is with CommRich
Limited and you should contact us rather than BT if you have any queries.
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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 CommRich 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.
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.
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.
NIC – Network Interface Card – a PC
expansion card that allows a PC to communicate with an Ethernet network via
appropriate cabling.
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 12 megabits per second).
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