3. RADSL (Rate-Adaptive Asymmetric Digital Subscriber
RADSL is an implementation of ADSL that automatically
adjusts the connection speed to adjust for the quality of
the telephone line. This feature allows RADSL service to
function over longer distances than does ordinary ADSL,
an important feature in suburban neighborhoods.
In RADSL, the broadband modem is configured at startup
to test the phone line and adjust the data rate. RADSL typically
operates at a lower date rate than regular ADSL. Like ADSL,
RADSL provides relatively more bandwidth for downloads and
less for uploads.
4. VDSL (Very-high-speed Digital Subscriber Line):Also
known as VADSL and BDSL
It was developed to support exceptionally high-bandwidth
applications such as High-Definition Television (HDTV).
VDSL is not as widely deployed as other forms of DSL service.
However, VDSL can achieve data rates up to approximately
51,840 Kbps, making it the fastest available form of DSL.
To perform at this speed, VDSL relies on fiber optic
cabling. VDSL is designed to work more as a business service
that uses ATM internetworking rather than as a consumer
service that utilizes IP. VDSL supports both voice and data
communication on the same line, like other forms of DSL.
Also like most DSL technology, the performance of VDSL
depends significantly on the physical distance traversed
by wires: Shorter distances mean faster networking. The
technology was originally named VADSL ('A' for asymmetric),
but VDSL has now been improved and can operate in either
symmetric or asymmetric modes.
The key to VDSL is that the telephone companies are replacing
many of their main feeds with fiber-optic cable. In fact,
many phone companies are planning Fiber to the Curb
(FTTC) , which means that they will replace all
existing copper lines right up to the point where your phone
line branches off at your house. At the least, most companies
expect to implement Fiber to the Neighborhood (FTTN).
Instead of installing fiber-optic cable along each street,
FTTN has fiber going to the main junction box for a particular