WHAT IS ADSL?
At the simplest level, ADSL is a high-speed replacement for your
modem or ISDN adapter that allows you to access the Internet faster.
The following diagram shows the maximum speeds attainable.
What does ADSL mean?
ADSL stands for Asymmetrical Digital Subscriber Line -it is the
transmission technique used on the line from your modem to your
service provider.
Asymmetrical: The speed of transmission is not the same in both
directions. The downstream (from network to consumer) speed can be
more than ten times as fast as upstream (from consumer to network).
This coincides nicely with the requirements for Internet access where a
single mouse click (therefore a small amount of data sent by the
consumer) can result in the receipt of a large amount of data from the
Internet.
ADSL stands for Asymmetrical Digital Subscriber Line -it is the
transmission technique used on the line from your modem to your
service provider.
Asymmetrical: The speed of transmission is not the same in both
directions. The downstream (from network to consumer) speed can be
more than ten times as fast as upstream (from consumer to network).
This coincides nicely with the requirements for Internet access where a
single mouse click (therefore a small amount of data sent by the
consumer) can result in the receipt of a large amount of data from the
Internet.
How does an ADSL Modem work?
ADSL exploits the unused analogue bandwidth that is potentially
available in the wires that run from the user premises to the local
exchange. This wiring was designed to carry that portion of the
frequency spectrum that is occupied by normal speech. The wires can,
however, carry frequencies above this rather limited spectrum. This is
the portion that ADSL uses.
The diagram above is approximate -voice typically uses the range
300Hz to 3,400Hz.
We can now see how voice and ADSL data can share the same
telephone line -in fact, splitters are used to ensure that the data and
voice do not interfere with each other.
The frequencies that the local loop can carry -and hence, the amount of
data transmission capacity that is available -depend on a number of
factors such as:
•the distance from the local exchange
•the type and thickness of wires used
•the number and type of joins in the wire
•the proximity of the wire to other wires carrying ADSL, ISDN and
other non-voice signals
•the proximity of the wires to radio transmitters.
ADSL exploits the unused analogue bandwidth that is potentially
available in the wires that run from the user premises to the local
exchange. This wiring was designed to carry that portion of the
frequency spectrum that is occupied by normal speech. The wires can,
however, carry frequencies above this rather limited spectrum. This is
the portion that ADSL uses.
The diagram above is approximate -voice typically uses the range
300Hz to 3,400Hz.
We can now see how voice and ADSL data can share the same
telephone line -in fact, splitters are used to ensure that the data and
voice do not interfere with each other.
The frequencies that the local loop can carry -and hence, the amount of
data transmission capacity that is available -depend on a number of
factors such as:
•the distance from the local exchange
•the type and thickness of wires used
•the number and type of joins in the wire
•the proximity of the wire to other wires carrying ADSL, ISDN and
other non-voice signals
•the proximity of the wires to radio transmitters.
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