The most common DSL variant is
asymmetric digital subscriber line (ADSL)
, and this is often
used for home and business users. It is called
asymmetric
because the bandwidth is not equal in
the upstream and downstream directions. Upstream traffic is sent from the user, and downstream
traffic is sent from the direction of the DSLAM.
When discussing a DSL circuit without specifying the type of DSL being used,
it is common to refer to xDSL.
This unequal traffic flow is well suited to Internet surfing and centralized data storage, as
would be found in many tele-worker applications. For example, many users download graphics,
documents, and other large files from the remote network, while only sending small e-mail messages
or requests for information. As such, the network needs to provide only a small amount
of bandwidth to service these smaller datagrams from the user, and it’s preferable to provide
larger amounts of bandwidth to support the greater volume of data from the network.
ADSL requires the use of a splitter to isolate the voice traffic from the data stream on the
copper pair.