DSL
DSL stands for
digital subscriber line, a technology
that transforms a traditional phone line into a high-speed digital link for broadband Internet access.
DSL provides a faster internet connection, Web site hosting, or branch offices
connection for individuals and small business.
There are several "flavors" of DSL.
These "flavors" vary in speed and other characteristics. Some
"flavors" are more suitable for consumer applications, while others are more suited for
business applications. Following are some of the remarkable differences in
characteristics among various "flavors" of DSL.
ADSL:
Asymmetric DSL offers a much higher speed downstream than upstream. ADSL is
typically offered as a consumer-grade service to compete with analog ISP
services, ISDN and cable modem services. Its low upstream speed means that it is
not optimized for services such as Web hosting, videoconferencing or any other
application where large amounts of data will flow out from the customer to the
Internet. ADSL utilizes frequencies above those used for analog Plain Old
Telephone Service (POTS) or ISDN. This feature enable voice services and DSL data
services to co-exist on a single copper pair.
SDSL: Symmetric DSL offers equal speeds both
upstream and downstream, and is typically offered in several different speed increments.
Typical offerings range from 144K bit/sec symmetric up to 2.3M bit/sec
symmetric. Unlike ADSL, SDSL is not compatible with analog POTS or ISDN over the
same line, so a second copper pair must be provisioned for the service.
IDSL: ISDN DSL provides DSL technology over
existing ISDN lines. Even though the transfer rates for IDSL are about the same
as ISDN (144k bit/sec vs. 128k bit/sec), the major benefit of switching to IDSL
from ISDN is an always-on connection, thus eliminating call set-up delays. IDSL
is transmitted over a data network, rather than the public switched telephone
network.
HDSL: High-bit-rate DSL is used to provide
T-1/E-1 services. HDSL is used as an underlying technology in the network for
the provisioning of T-1/E-1 services. Unlike ADSL and SDSL, HDSL uses two copper
pairs (four wires), not a single pair - although another "flavor" of
HDSL, known as HDSL2, using a single copper pair is now available.
VDSL: The fastest "flavor" of DSL,
very- high bit rate DSL is another emerging service. VDSL has a much shorter
range than other DSL variants, but will offer speeds up to 52M bit/sec
downstream in an asymmetric mode, or 26M bit/sec both direction in a symmetric
mode. Because of its high speeds and short range, VDSL is more suited for carrying
video and other high-speed services in residential and campus environments where
the equipment can be located close to all end users.
G.shdsl: The new generation of SDSL, based on a
new international standard from the International Telecommunications Union.
G.shdsl offer speeds and symmetric services similar to SDSL but with a 30%
greater service range.
Advantages
