Types of DSL

ADSL or Asymmetrical Digital Subscriber Line is most typically used for access to the Internet at home. The capacity of the circuit is greater coming from the Internet into the home (called downstream)than going the other direction (called upstream). This is because home users are more likely to receive more information(graphics, sound, and video) than they send (keystrokes and mouse clicks).

SDSL or Symmetrical Digital Subscriber Line is the type used by most businesses who need to send as well as receive significant amounts of information. The capacity of the circuit is the same in both directions.

The capacity affects how quickly the screen on your computer will display the information from the Internet or how quickly you can send a computer file from your office to another location. If you are sending large files with pictures, you will need a higher-capacity DSL circuit than if you are sending regular text files or text email. The capacity of the circuit also needs to be greater if several people will be using it at the same time.(You can connect to DSL through a computer server that is shared with other people in your office.)

Determining the capacity of the DSL circuit that's right for you may require a bit of trial and error. You can pay the highest rate and order the greatest capacity or order a lower capacity and see if it's sufficient. The capacity of the DSL can be changed by your service provider, usually within a few days.

Capacity specifically refers to the volume of information that can travel over the circuit within a given time frame. Typical capacities are 128Kbps(kilobits per second - meaning that 128,000 bits can pass a point on the circuit in one second. 256Kbps, 512Kbps, 768Kbps (a popular mid-range speed), 1Mbps (mega bits per second),1.5Mbps is the approximate capacity of T-1 telecommunications circuit that traditionally costs more than DSL.

You may hear about other types of DSL which are all variations on the theme. HDSL (high bit-rate DSL) has a speed of 1.544Mbps and uses either two or three pairs of copper wires instead of one pair. IDSL (ISDN DSL)has the same speed - 128Kbps or 144Kbps - as another service called ISDN(Integrated Services Digital Network) which requires dialing HDL into the Internet on a special type of line delivered on a pair of copper wires. DSL Lite(also called G-Lite) is a lower-speed version of ADSL. RADSL is Rate Adaptive DSL that adjusts the speed of the transmission based signal quality. VDSL is a Very High Speed DSL (12.9 to 52.8Mbpsdownstream and 1.5 to 2.3 Mbpsupstream).

What Is x-DSL?

One of the major problems facing the ILECs was the ability to maintain and preserve their installed base. Ever since the Telecommunications Act of 1996, the ILECs have faced mounting pressure to provide faster and more accurate Internet access. Therefore, a new form of communications was needed to work over the existing copper cable plant. One of the technologies selected was the use of DSL. The DSL family includes several variations of what is known as digital subscriber line (DSL). The lowercase x in front of DSL stands for the many variations. These will include

• Asymmetric digital subscriber line (ADSL)

• ISDN-like digital subscriber line (IDSL)

• High-bit-rate digital subscriber line (HDSL)

• Consumer digital subscriber line (CDSL)

• Rate-adaptive digital subscriber line (RADSL)

• Very high-speed digital subscriber line (VDSL)

• Symmetric or single digital subscriber line (SDSL)

• Single-pair high-speed digital subscriber line (SHDSL)

One can see that many variations are available. Each digital subscriber line (DSL) capability carries with it differences in speed,throughput, and facilities used. The most popular of this family under today's technology is asymmetrical digital subscriberline (ADSL). ADSL is a technology primarily provided by the ILECs because the existing cable plant can support the speeds, which can vary depending on the quality of the copper. The Competitive Local Exchange Carriers (CLECs) are quickly becoming involved in providing xDSL now. However, the most important and critical factor in dealing with ADSLtechnology is the capability to support speeds from 1.5 up to 8.192 Mbps. The ILECs can also support POTS for voice or fax communications on the same line.This means that the ILECs do not have to install all-new cabling to support high-speed communications access to the Internet, which is burning up the wires today.