Summary
In this blog, you learned that digital subscriber line (DSL) technology was developed to add
functionality to the large existing copper cable plant installed for the analog phone system. The
service is built around ATM technology and provides a wide variety of flavors to offer different
data rates and service distances. DSL variants range in bandwidth from 144Kbps to over 50Mbps.
Unlike other WAN technologies, many DSL flavors are asymmetric; that is, they provide different
bandwidths in upstream and downstream directions.
We described the configuration and troubleshooting elements of DSL, while noting that from
the transport point-of-view, DSL is examined the same as ATM. We also noted that DSL sometimes
uses complex bridging and routing solutions to simplify larger deployments. DSL is a consumer
service in many installations, and with over 28 million installations (as of late 2003),
simple, repeatable deployments are crucial. To that end, we described the primary feature of
G.lite, or splitterless DSL.
Exam Essentials
Understand how DSL can fit into your remote access solutions. DSL is well suited to
remote workers and small branch offices for remote connectivity. It offers many of the same
bandwidths as T-1 at lower prices, and, in some cases, its asymmetric offerings are perfect
for high-demand users.
Know the differences in the various flavors of DSL. The DSL service offerings are best
considered in terms of bandwidth and analog voice support. G.lite is a splitterless offering
that provides for analog voice without a splitter in the line. HDSL and SDSL provide symmetric
bandwidth.
Be able to compare DSL to other remote access technologies. HDSL and SDSL both provide
bandwidths comparable to T-1 services. This can be very important for the administrator—for
example, T-1 might not be available but HDSL is, and, ironically, HDSL might be cheaper.
Other xDSL services can be replacements for Frame Relay or other access methods.
Understand the configuration of DSL services. The key to configuring DSL services is to
understand their relationship to ATM in the networking model. DSL commonly uses the same
PVC configuration and other logical constructs.