Digital subscriber line (DSL) provides higher-speed Internet access over existing telephone lines. It uses frequencies that do not interfere with voice calls to transmit data faster than a conventional modem. The most popular type of DSL is asymmetric DSL (ADSL), which allocates more bandwidth to downstream data transmission from the telephone central office to the user than to upstream transmission. ADSL uses the discrete multitone technique to maximize data rates over existing copper telephone lines.

1. DIGITAL SUBSCRIBER LINE
After traditional modems reached their peak data
rate, telephone companies developed another
technology, Digital subscriber line (DSL), to provide
higher-speed access to the Internet.
9.1

2. DSL (Digital Subscriber Line)
• Use existing telephone lines, DSL integrates regular phone service and
Internet access by using a DSL hub.
• “Always Connected" situation.
• Maximum speed may be limited by the physical distance from a
telephone company central office (CO) to the computer
(ISDN (Integrated Services Digital Network) is a technology developed in the 1980s that
uses regular telephone lines, and is accessed by a dial-up connection. ISDN is actually
an early implementation of DSL.)
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3. •Stands for Asymmetric Digital Subsriber Line
• The most popular version of DSL
• It is called “Asymmetric” because the bandwidth is not the same :
Downstream > Upstream
•Utilizes frequencies that are not used by a voice telephone call, therefore it has
faster data transmission over copper telephone lines than a conventional
voiceband modem
• Reason of popularity – Residential users prefer greater download speed than upload
speed
9.3

4. Bandwidth division in ADSL
The upstream band is used for communication from the end user to the
telephone central office(CO). The downstream band is used for communicating from the
central office to the end user.
*The existing local loops can handle bandwidths up to 1.1 MHz.
9.4

5. Discrete multitone technique
*DMT expands the usable bandwidth of existing copper telephone lines, delivering high-speed data communications
9.5

6. ADSL modem
•Local loop – The physical link or circuit that connects from the customer premises to
the edge of the telecommunications service provider's network(EG: Telekom).
9.6

7. DSLAM
• DSLAM - digital subscriber line access multiplexer
• A place where another frequency splitter separates the voice band signal for the conventional phone
network. Data carried by the ADSL are typically routed over the telephone company's data network
and eventually reach a conventional Internet Protocol network.
9.7

8. Summary of DSL technologies
• HDSL was the first DSL technology to use a higher frequency spectrum of copper, twisted pair cables
• SDSL offer symmetric bandwidth upstream and downstream - a particular DSL variant that supports data only
on a single line and does not support analog calls
•Very-high-bit-rate digital subscriber line capable of supporting applications such as high-definition television,
as well as telephone services (voice over IP) and general Internet access, over a single connection
• 2B1Q Two- binary, one- quaternary
9.8