Asymmetric digital subscriber line is a type of digital subscriber line technology, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide. ADSL differs from the less common symmetric digital subscriber line.
ADSL is a popular, older type of broadband, with the term standing for Asymmetric Digital Subscriber Line. It is a broadband connection that works through the copper wires of existing phone lines and is mainly used for home broadband and within small businesses.
What is difference between DSL and ADSL?
DSL (Digital Subscriber Line) denotes an internet that uses digital connections between a modem and a phone line. ADSL means Asymmetrical Digital Subscriber Line where the speed of data sent is known as upstream and data received is known as downstream.
Characteristics of ADSL
In an ADSL connection, three independent transmission lines are established:
- Data transmission channel. Where the user’s information will be sent to the Internet (upload).
- Data reception channel. Where the information will be received from the Internet (download). It will be the widest of the three channels.
- Regular telephone service channel. Where the telephone calls will be transmitted.
This separation allows a differentiated handling of data and transmission impulses, and can even be improved in the versions known as ADSL2 and ADSL2+, which also receives a channel for the transmission of subscription television (cable TV) and high quality video.
DSL family is collectively referred as xDSL. There are various different types such as IDSL, HDSL, SHDSL, RADSL, UDSL, VDSL, GDSL as outlined with their data rates, bandwidth allocations and maximum coverage distances. The most popular ADSL (Asymmetric ADSL) provides downstream data rate of about 8Mbps and upstream data rate of about 500Kbps.
The IDSL is the short form of Integrated DSL. It delivers data rate of 144Kbps for maximum distance of about 5.4 Km.
The HDSL is the short form of High bit rate DSL. It is symmetric technology. It delivers data rate of 2.048Mbps for maximum distance of about 4.6 Km. It uses pair of copper wires.
The SHDSL is the short form of single pair high speed DSL. It delivers data rate of about 384Kbps to 4.608Mbps. The step size is about 128Kbps.
The RADSL is the short form of Rate adoptive DSL. This version of DSL adjusts its downstream data rate and upstream data rate as per line noise and distance required to be covered.
The UDSL is the short form of Uni-DSL or Universal DSL. It delivers downstream and upstream data rate of about 200Mbps.
The VDSL is the short form of Very High Speed DSL. It is symmetric and delivers downstream data rate of about 13 to 52Mbps and upstream data rate of about 1.5Mbps to 2.3 Mbps using single copper line. It covers distance of about 300meters to 1.4Km from exchange.
The GDSL is the short form of Gigabit DSL. It is based on MIMO concept. It delivers data rate of about 1Gbps over distance of about 300 meter.
Ethernet local loop incorporates features of both ethernet and DSL. It delivers data rate speed of about 6Mbps over distance of 6.5Km.
ADSL Standards or versions
Various ADSL standards or versions with their respective standard, upstream data rate and downstream data rate is mentioned in the following table.
|ADSL Version||ADSL Standard||Upstream data rate||Downstream data rate|
|ADSL||ANSI T1.413-1998 issue 2||1Mbps||8Mbps|
|ADSL G.DMT||ITU G.992.1||1.3Mbps||12Mbps|
|ADSL over POTS||ITU G.992.1 annex A||1.3Mbps||12Mbps|
|ADSL over ISDN||ITU G.992.1 annex B||1.8Mbps||12Mbps|
|ADSL Lite||ITU G.992.2||512Kbps||1.5Mbps|
|ADSL2||ITU G.992.3 annex J||3.5Mbps||12Mbps|
|RE-ADSL2||ITU G.992.3 annex L||800Kbps||5Mbps|
|Splitter less ADSL2||ITU G.992.4||500Kbps||1.5Mbps|
|ADSL2+M||ITU G.992.5 annex M||3.5Mbps||24Mbps|
Advantages of ADSL
Each subscriber receives an independent and non-transferable service directly to their home.
It doesn’t occupy the telephone line. This represents an advantage when installing the service in homes and companies, as it allows the autonomy of both services, something impossible with the dialing method.
It employs traditional infrastructure. It does not require new and extensive investments or major works, as it takes advantage of traditional copper cabling.
Outperforms dial-up connection. It offers a much better speed/price ratio than dialing methods, which in addition to occupying the telephone line usually go to 56 kps, while ADSL can reach 4mbps (70 times faster).
Allows central and customized circuits. Because it uses telephone cables, each subscriber receives an independent, non-transferable service directly to their home or office.
Disadvantages of ADSL
- It doesn’t operate on every phone line. It is not enough to have a telephone connection by copper cabling to use ADSL, as this technology has a limit of 3km of line length from the central transmitter.
- ADSL demands copper quality. In countries where this material is expensive or scarce the service may not be as inexpensive as in others.
- It depends on external factors. The quality of the service is subject to the quality of the cables, the distance from the plant and fluctuations in the flow of the service.
- It’s far inferior to fiber optics. Fiber optic connections far outperform ADSL in stability and speed.
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