ADSL
Frequently Asked Questions
What
does ADSL stand for?
How does ADSL Work?
I've also heard of RADSL. What is this?
What is Contention?
At what speeds can I connect with ADSL?
Aren't all ISP's ADSL services the same?
Is ADSL available to everyone?
How will ADSL compare with a Dial-up connection?
How will ADSL compare with ISDN/Highway?
Will ADSL work on any telephone line?
Will I need to change my telephone number?
Will I still be able to make telephone calls
through my ADSL line?
Will I still need to pay for my telephone
line rental and telephone calls?
Will other BT services such as 'Call Waiting'
still work?
Can I connect ADSL to my Company's internal
telephone network?
What
are the minimum specifications of my PC to be able to use
ADSL?
I have an Apple Mac can I use ADSL?
What does ADSL stand for?
It stands for Asymmetric Digital Subscriber Line. It is
called "asymmetric" because it moves data faster
from the telephone exchange to the customer than from the
customer to the exchange. This makes it particularly suitable
for applications where the customer expects to receive more
data than they transmit. An excellent example of this is
Internet "surfing", where more information is
received than is sent.
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How does ADSL Work?
The copper wires that are used to carry telephone lines
into most homes and offices are capable of transmitting
much more information than is necessary to convey a telephone
conversation. ADSL is able to take advantage of this extra
bandwidth by transferring data at a higher frequency than
that used for voice calls. Sophisticated electronics are
employed to cope with electrical noise on the line and to
ensure that there is no interference between the voice and
data sharing the line.
The
high frequencies that are used to send the signal degrade
with distance, as a result there are limits that the signal
can be reliably received. The 512K ADSL services have a
maximum range of 5.5 km. and because of the higher bandwidth
required, the 1MB and 2Mb ADSL services have a slightly
smaller radius of 3.5km.
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I've
also heard of RADSL. What is this?
RADSL (Rate-Adaptive Digital Subscriber Line) is the very
latest advancement in Broadband technology. It has been
created to allow more customers to receive the Torsion 512K
ADSL services by increasing the range of ADSL from 3.5km
to 5.5km. This enhancement has been made to increase the
availability of Broadband Internet access to the UK population.
Whilst
the download speed available to customers using RADSL is
not affected, the upload speed will be negotiated every
time an attempt to send data across the Internet is made
and will vary between 64kbps and 256kbps.
All
512K ADSL connections now use RADSL technology.
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What
is Contention?
Contention
is basically sharing. Your electricity is contended - normally
not a problem as there's more than enough to go around.
Everything in life is contended.
Unlike
a leased line which provides guaranteed bandwidth, with
ADSL the available bandwidth is shared between a predetermined
number of other users. For example, if the service is contended
at 20:1, it means that you share the bandwidth with up to
19 other users. Thus the performance of an ADSL connection
will vary according to time of day and day of the week,
depending on how many other users happen to be online at
that moment.
The Contention ratios available with ADSL are either 50:1
or 20:1 depending on the ADSL service you choose. The lower
the contention ratio the better chance of reaching the optimum
data transfer speeds.
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At
what speeds can I connect with ADSL
The use of ADSL technology will allow download speeds from
the Internet at up to 2Mbps, while traffic in the upstream
direction travels at a maximum of 256Kbps. However, there
are a number of factors that can affect the actual data
rate achievable; the main factors being:
- Distance
- The 512K ADSL services have a maximum range of 5.5 km.
Because of the higher bandwidth required, 1 MB and 2Mb
ADSL services have a slightly smaller radius of 3.5km.
- Quality
of the Line - Much of the cable infrastructure in
the UK has been in place for many decades and any problems
with the cables can dramatically reduce effectiveness.
Sharp bends and frayed cables will not affect voice data,
but can impair a high frequency ADSL signal. The launch
of RADSL can help here too. RADSL technology enables the
ADSL signal to be successfully sent over telephone lines
that were previously of too poor quality to receive an
ADSL signal.
- Contention
Ratio - Unlike a leased line which provides guaranteed
bandwidth, with ADSL the available bandwidth is shared
between a predetermined number of other users. For example,
if the service is contended at 20:1, it means that you
share the bandwidth with up to 19 other users. Thus the
performance of an ADSL connection will vary according
to time of day and day of the week, depending on how many
other users happen to be online at that moment.
The Contention ratios available with ADSL are either 50:1
or 20:1 depending on the ADSL service you choose. The
lower the contention ratio the better chance of reaching
the optimum data transfer speeds.
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Aren't
all ISP's ADSL services the same?
Although all ISPs offer the same range of ADSL services
and every ADSL customer will connect to BT equipment on
a BT local exchange, the quality of the ADSL services you
will receive will vary depending on the ISP you choose.
When
an ISP creates the infrastructure of their ADSL service,
they must choose the amount of bandwidth required to connect
customers from the BT local exchanges to the ISP's backbone.
Because of the high cost of this connection, many ISP's
have elected to use the smallest possible connection available
and oversubscribe the connection. This means that customers
have less bandwidth available than they should.
The
ISP's own backbone can also affect the speed available to
customers. As the implementation and availability of ADSL
increases, large downloads will become commonplace. Because
of the always-on nature of ADSL, these high bandwidth demands
can be made any time of the day or night. If the ISP you
choose does not have enough bandwidth on their backbone,
you may find the quality of your ADSL service is not what
you would expect. As ADSL becomes more popular, you could
even find the level of service you receive decreasing.
Torsion
Internet have a reputation for providing high quality Internet
access, and our ADSL services are no different. We are committed
to ensuring that we use the largest connection available
to connect our customers from BT's local telephone exchanges
to the network.
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Is
ADSL available to everyone?
No. In order to receive an ADSL service, customers must
have a standard BT telephone line which is connected to
an ADSL enabled local telephone exchange and is within 5.5km
from the exchange for a 512K service or 3.5km for a 1Mb
or 2Mb service.
At
present approximately 70% of UK households and businesses
are connected to an ADSL enabled exchange.
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How will ADSL compare with a Dial-up connection?
There are a number of differences between an ADSL Internet
connection, and a Dial-up Internet connection:
- Price
- ADSL connections will cost more than a standard Torsion
Internet Dial-up connection. This is simply because ADSL
offers far superior connection speeds and provides you
with a 24-hour a day, 7 day a week connection, all for
a fixed monthly fee which includes the cost of Internet
calls.
- Speed
- The fastest access speeds currently available through
standard analogue modems are 56.6 Kbps for download (data
from the Internet) and 33.6 Kbps upload (data to the Internet).
ADSL will provide speeds of up to 2Mbits for download
and a maximum 256 Kbps upload. And because you would be
connected all day every day, you don't have to wait while
you establish a connection before browsing the web or
downloading email The download speeds available will be
512Kbps, 1Mbs or 2Mbps depending on the ADSL service chosen.
- Contention
Ratio - When we refer to a contention ratio, we are
referring to how many people would be connected to the
network at any given time. For Dial-up access it would
be modems hosted by us, for ADSL it would be your local
BT exchange. For ADSL, the more people that connect to
the exchange using ADSL the slower the service will be.
The contention ratios will be either 50:1 or 20:1 depending
on the ADSL services you have chosen.
- Availability
- With a Torsion Internet Dial-up connection as long
as you have a computer, modem and telephone line you can
connect to the Internet through Torsion Internet regardless
of who provides your telephone service or where you live.
ADSL is only available to those businesses that have the
special hardware fitted to their local telephone exchange
by their telephone provider. Currently BT is the only
telephone company capable of providing ADSL.
In addition, because of the distance limitation, ADSL
will not be available to premises more than approximately
5.5km away from their local telephone exchange. It is
also sensitive to the quality and maintenance standard
of the copper wire used within the telephone line, so
not everyone within the 5.5km limit will be able to take
advantage of ADSL.
Please
note: Only the 512K ADSL services have a radius of 5.5km.
If you require a 1MB or 2Mb ADSL service the radius is 3.5km.
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How
will ADSL compare with ISDN?
- Price
- Depending on the ADSL service you choose, ADSL is
comparable in price to ISDN whilst offering significant
advantages including permanent connectivity and greater
speeds, all for a fixed monthly cost. With ISDN you will
be required to pay a monthly line rental fee and both
Internet call charges and voice call charges. With ADSL
you pay your line rental and a single monthly fee which
covers the cost of your Internet access and Internet call
charges. You would still be charged for standard voice
calls by your telephone provider.
- Speed
- Under optimum operating conditions ADSL will generally
offer higher download speeds than would be obtained using
ISDN. It may not offer any speed improvement when sending
data out to the Internet however. Speed advantages aside,
ISDN will always deliver the same consistently high level
of performance regardless of how many people connect to
the local telephone exchange, whereas the performance
of ADSL very much depends on how many people that have
ADSL connect to the same exchange at the same time. However,
at its best, ISDN is only capable of transferring data
at 64kbps unless 2 channels are used to transfer data.
This would result in two sets of telephone charges. ADSL
can send data over 30 times faster than a standard ISDN
line all for a fixed fee. We anticipate that all Torsion
Internet ADSL services will even outperform an ISDN connection
where two channels are being used.
- Asymmetry
- ADSL is asymmetric because most of its two-way or duplex
bandwidth is devoted to the downstream direction, sending
data to the user. Only a small portion of bandwidth is
available for upstream or user-interaction messages, whereas
ISDN (or BT's Highway service) is symmetric because the
data rate is the same in both directions.
- Always
on - ADSL-based Internet access is a 24-hour a day,
7 day a week connection meaning there is no wait while
you connect to the Internet. ISDN does require you to
dial-up and connect to the Internet when access is required.
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Will ADSL work on any telephone line?
No, ADSL is only available to customers using a standard
BT telephone line of sufficient quality that falls within
the radius of 5.5k for our 512K services and 3.5k for our
1Mb or 2Mb services.
Your
line MUST not be connected to your PBX, it must be a line
independent of your internal telephone exchange system.
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Will
I need to change my telephone number?
No, because ADSL has been designed to use your existing
BT telephone line, your telephone number remains the same.
If you use an alternative telephony provider, you will be
required to install a BT telephone line in order to receive
ADSL. This may mean a change in telephone number.
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Will I still be able to make telephone calls through
my ADSL line?
Yes, ADSL will allow you to make telephone calls even while
you are accessing the Internet. If you make calls whilst
connected to the Internet through ADSL, you may notice a
slight drop in the connection speed. This is because when
a telephone call is made, a small piece of the ADSL bandwidth
is used for the call.
Please
note: You will still be charged for voice calls in the normal
metered way.
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Will I still need to pay for my telephone line rental
and telephone calls?
Yes, ADSL only enables you to use the Internet without paying
ongoing call charges to BT. Your standard voice telephone
calls and line rental will be charged by BT in the normal
way.
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Will other BT services such as 'Call Waiting' still work?
Yes they will. BT Select Services such as Call Waiting,
Call Return and Caller Display will all continue
to be supported by BT.
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Can I connect ADSL to my Company's internal telephone
network?
No.
ADSL is only available on a standard BT telephone line terminating
via a standard BT telephone socket. ADSL will not work with
any type of telephone switch equipment.
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What
are the minimum specifications of my PC to be able to use
ADSL?
For
use on a single machine via a USB port click
here for minimum machine specifications
For
use with a network click
here for minimum machine specifications
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I
have an Apple Mac can I use ADSL?
ADSL
is compatible for use with Apple Mac computers and we can
connect your Macs and PC's on the same connection
For
use on a single machine via a USB port you will require
a Macintosh with at least 1 USB port.
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FAQ Disclaimer:
Although we will of course endeavour to ensure that the
information included within this FAQ is accurate and up-to-date,
we cannot guarantee that it is exhaustive, or that changes
won't be made at any time without prior notice.
