DSL ISP Info
A brief history about DSL and it's development.

DSL Service Providers
Some top DSL providers and plans they offer to consumers.

What Is DSL
An introduction to the technology and driving force behind it.

How It Works
Learn how DSL works and related hardware that make the technology possible.

Types of DSL
ADSL, SDSL, SHDSL, IDSL and more ...

Advantages And Disadvantages
Look at some of the principal advantages and disadvantages of the DSL.

How DSL Works ?

DSL relies solely on the old telephone technology which is called Plain Old Telephone Service or POTS for short. POTS operate by limiting the frequencies carried by its equipment including switches, receivers, transmitters, etc. The reason for this limitation is that, the human voice can be carried across a telephone line at the frequency of 3400 Hertz although the wires have the potential to transmit 20000 hertz. The reason for limiting the frequency is that, it allows the telephone system to cram a lot of wires into a small space without causing jamming between lines.

DSL carries data in two of one ways; through the Discrete Multi-tone (DMT) or the carrierless amplitude/phase (CAP) system. DMT segregates signals into 247 separate channels, each 4 KHz wide. CAP rather divides the signals on the line into three frequency bands: 0 to 4 KHZ to manage telephone conversations, 20 to 130 for carrying data from the user to the server and 140+ KHZ to download information from the server to the ser PC. The reason for the splitting of the channels id is to prevent interference of channel into the other., minimizes the possibility of interference between the channels. DSL uses filters to segregate one frequency channel from the other so that telephone conversations do not stray into the broadband signals.

DSL uses two principal devices. One of these can be found on the user's premises and the other is located at the provider’s office. At the customer's end, you can find a transceiver and at the provider’s, an Access Multiplexer (DSLAM).

Now let’s examine the functions of these two pieces of equipment.

TRANSCEIVER (DSL Modem)
Technically, it is referred to as ATU-R. The function of this device is to serve as a point at which user data is connected t the DSL line.

DSLAM
The DSLAM, located at the premises of the provider is the core equipment that controls the technology. The function of this device is to accept DSLAM connections from several users and bundle them onto a single connection to the Internet. DSLAM can support different kinds of DSL and protocol varieties, including CAP and DMT. DSLAM can additionally serve as a router or assign IP addresses to users.

Actually, it is the DSLAM that provides one of the core differences between a cable and DSL connection. This device provides a dedicated connection for each user so there is no loss of speed as new users are added unlike cable connection.