What Is Dsl; What Is Adsl - ZyXEL Communications Prestige 642 User Manual

Prestige 642 PPPoE Modem

What is DSL?

DSL (Digital Subscriber Line) technology enhances the data capacity of the existing telephone line running
between the local telephone company switching offices and most homes and offices. While the wire itself can
handle higher frequencies, the telephone switching equipment is designed to cut off signals above 4,000Hz to
filter noise from the voice line. DSL services are either symmetrical (traffic flows at the same speed in both
directions) or asymmetrical (the downstream capacity is higher than the upstream capacity).
As the carrying distance increases, data rates decrease. That means that users who are beyond a certain
distance from the telephone company's central office may not be able to obtain the higher speeds for DSL
maximum transmission distances. A DSL connection is a point-to-point dedicated circuit, meaning that the
link is always up and there is no dialing required.

What is ADSL?

ADSL is an asymmetrical technology, meaning that the downstream data rate is much higher than the
upstream data rate. This works well for a typical Internet session in which more information is downloaded,
e.g., from Web servers, than is uploaded. ADSL operates in a frequency range that is above the frequency
range of voice services, so the two systems can operate over the same cable.
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