ADSL
The ADSL (from the abbreviations in Asymmetric Digital Subscriber List that translates Asymmetric Digital Subscriber Line) is a type of technology of digital data transmission and Internet access , which consists of the transmission through symmetrical pairs of telephone line copper. This is, a method of accessing the Internet through the telephone line (Telephone Network Switched, PSTN) that does not prevent the regular use of the line for calls.
The ADSL is a type of broadband connection , whose name comes from the fact that the capacity of download (from the network to the computer) and load (from the computer to the network) are not coincident, but the first is greater than the second. After all, most Internet users receive more information than they emit.
It can serve you: FTP
For the ADSL to work, it is necessary to have a telephone line and a modulation system that separates the frequencies of the voice and data , by installing discriminating filters (called splitters , micro filters or DSL filters) and an ADSL router. provided by the company that provides the service.
This type of copper urban wiring was traditionally implemented, but in the final decades of the 20th century it was gradually replaced by fiberglass, a material that offered better driving and performance, thus accommodating even better methods of digital information transmission, such as the cable modem or the Ethernet.
ADSL is a technology access to Internet of broadband , which implies a speed higher than a wired modem in data transfer because the modem uses voice band and thus prevents voice service while use and vice versa. This is achieved by modulating the data signals in a higher frequency band than that used in conventional telephone conversations (300 to 3400 Hz ), a function performed by the ADSL router . To avoid distortions in the transmitted signals, you need to install a filter (discriminator, DSL filter ) which is responsible for separating the conventional telephone signal from the modulated signals of the connection through ADSL.
This technology is called “asymmetric” because the download capabilities (from the network to the user) and data upload (in reverse) do not match. ADSL technology is designed so that the download or download capacity is greater than the upload capacity, which corresponds to the use of the Internet by most end users, who receive more information than they send (or download more of what goes up).
See also: Difference between DSL and ADSL with table
In an ADSL line, three communication channels are established :
Obtaining these three channels can be done using two techniques: The first consists of using FDM to assign a band to both the upstream and downstream data channel, these two bands are in turn divided into sub channels using TDM, these channels can be high and low speed. The second technique is Echo Cancellation, used in very specific analog modems such as V.32 and V.34 ITU-T.
Telephone companies implement improved versions of this technology, such as ADSL2 and ADSL2 + , with the capacity to supply high-quality television and video through the telephone pair . It involves tough competition between telephone companies and cable operators , and the appearance of integrated voice , data and television offers , from the same line and within a company or several, that offers these three communication services through the same medium. : Triple play . The use of higher bandwidth for these services further limits the distance that the pair of wires can operate.
ADSL2 and ADSL2 + incorporate advanced physical resource management and modulation mechanisms, so that they not only increase the capacity of conventional ADSL from 8 Mbit / s to 12 and 24 Mbit / s respectively, but also introduce improvements to avoid interference or noise, and reduce the effects of attenuation, hence distances of up to 9 km [ citation needed ] .
ADSL is a technology that uses the copper pair and has less bandwidth than other technologies such as cable modem or Metro Ethernet [ citation required ] , whose urban cabling is made up of fiber optic wires instead of the copper pair implemented in its greatest part in the 1950s and 1960s.
See also: What is the ISP?
As with other digital transmission systems, ADSL serves as a channel for the transmission of digital data and connection to the Internet .
This means that it is a virtually unlimited source of information and online services , with all that this implies. This method of connection was key in the massification of the Internet in homes and urban environments during the 1990s.
Must Read: What is digital television? (TV)
In an ADSL connection , three independent transmission lines are established:
This separation allows a differentiated handling of data and transmission pulses, and can even be improved in the versions known as ADSL2 and ADSL2 +, in which a channel for the transmission of subscription television (cable TV) and video is also received. of high quality (HD).
Read: Difference Between DSL Modem And Cable Modem In Tabular Form
Must Read: Difference between modem and router with table
The history of the development of ADSL technology starts in the second half of the eighties, when the search for technology was carried out to provide interactive television . Bellcore is a pioneer of the xDSL family of technologies . In 1987, it introduced the specification of the first technology from the xDSL family and launched it on the US telephone networks . The company soon fell apart, and the technology lay low.
In the mid -1990s, the xDSL family was supplemented by an asymmetric modification of the digital subscriber line – ADSL. In the following years, chipsets were created and improved to carry out data transmission via ADSL. The pace of development was slow because DSL was originally designed for video-on-demand systems. The systems themselves did not get widespread, and the ADSL technology got a second wind thanks to the development of Internet networks .
With the advent of the first ADSL modems, providers saw the promise of this technology and began to use it to provide access to the network. For the need to install equipment on each PBX, the costs of building and maintaining the network were noticeably higher than in the case of classic dial-up access, when all the provider’s modems were installed on one PBX , however, compared to the cost of other methods of providing high-speed Internet access, DSL technology turned out to be very cheap.
In large cities, ADSL is being supplanted by faster access technologies Ethernet ( ETTH ), GPON ( FTTH ) and DOCSIS (data over cable television standard). The reason for this is the limited bandwidth in ADSL networks (up to 24 Mbit / s in ADSL2 +), especially the “upstream” from the subscriber (up to 1.4 Mbit / s), while EuroDOCSIS 2.0 provides a data transfer rate of 50 ↓ / 27 ↑ Mbit / s, Fast Ethernet – up to 100 Mbit / s, Gigabit Ethernet – up to 1 Gbit / s, 10 Gbit / s EPON – up to 10 Gbit / s.
Despite the emergence of faster data transmission methods, ADSL technology is still the leader in the broadband data transmission market. In a number of European countries, ADSL is the de facto standard for providing the population with a fairly fast and inexpensive Internet. So, in Finland, where every inhabitant of the country has been guaranteed access to the Internet since June 2010, most houses are connected using ADSL technology , and British Telecom has provided the ability to connect services using ADSL technology to 99% of UK buildings .
This frequency division allows you to talk on the phone without interrupting the communication on the same line. Of course, situations are possible when either the high-frequency signal of the ADSL modem negatively affects the electronics of a modern phone, or the phone, due to any peculiarities of its circuitry, introduces extraneous high-frequency noise into the line or greatly changes its frequency response in the high-frequency region; to combat this directly to the telephone network subscriber in the flat low-pass filter set ( frequency divider , Engl. Splitter), which passes only the low-frequency component of the signal to ordinary telephones and eliminates the possible influence of telephones on the line. Such filters do not require additional power supply, so the voice channel remains operational when the power supply is disconnected and in the event of a malfunction of the ADSL equipment.
Transmission to the subscriber is carried out at speeds up to 10 Mbit / s, although today there are devices that transmit data at speeds up to 25 Mbit / s ( VDSL ), however, this speed is not defined in the standard. In ADSL systems, 25% of the total speed is allocated for overhead information, in contrast to ADSL2 , where the number of overhead bits in a frame can vary from 5.12% to 25%. The maximum line speed depends on a number of factors such as line length, cross-section and cable resistivity. Also, a significant contribution to the increase in speed is made by the fact that twisted pair is recommended for the ADSL line (not TRP ) and shielded, and if it is a multi-pair cable, then in compliance with the direction and pitch of the twist.
With ADSL, data is transmitted over a common pair in full duplex form. In order to separate the transmitted and received data stream, there are two methods: frequency division multiplexing ( Engl. Frequency Division Multiplexing , FDM) and echo cancellation ( Engl. Echo Cancellation , EC)
When using this mechanism, the low-speed data channel is located immediately after the frequency band used for the transmission of analog telephony. The high speed channel of received data is located at higher frequencies. The bandwidth depends on the number of bits transmitted by one signal.
The subscriber telephone line , when used for ADSL technology, must have the following parameters:
The following are the norms for operating attenuation and a chain length of 1 km:
Noise Level (RMS Noise Energy (dB re 1 mW @ 600 ohm load)):
S / N ratio (Signal-to-Noise Ratio ( SNR ), noise margin (Noise Margin)):
For ADSL lines, it is recommended to use twisted pair (and not ” noodles “), otherwise the bandwidth of the data transmission channel is reduced.
Name of the standard | Common name | Downstream speed, Mbps | Upstream speed, Mbps | Approved in |
---|---|---|---|---|
ANSI T1.413-1998 Issue 2 | ADSL | 8.160 Mbps | 1.216 Mbps | 1998 |
ITU G.992.1 | ADSL ( G.DMT ) | 8 Mbps | 1.3 Mbps | 1999-07 |
ITU G.992.1 Annex A | ADSL over POTS | 12 Mbps | 1.3 Mbps | |
ITU G.992.1 Annex B | ADSL over ISDN | 12 Mbps | 1.3 Mbps | |
ITU G.992.2 | ADSL Lite ( G.Lite ) | 1.5 Mbps | 0.5 Mbps | 1999-07 |
ITU G.992.3 | ADSL2 | 12 Mbps | 1.216 Mbps | 2002-07 |
ITU G.992.3 Annex A | ADSL2 over POTS | 12 Mbps | 1.216 Mbps | |
ITU G.992.3 Annex B | ADSL2 over ISDN | 12 Mbps | 1.216 Mbps | |
ITU G.992.3 Annex J | ADSL2 | 12 Mbps | 3.5 Mbps | |
ITU G.992.3 Annex L | RE-ADSL2 | 5 Mbps | 0.8 Mbps | |
ITU G.992.3 Annex M | ADSL2 ( G.DMT.bis.plus ) | 12 Mbps | 3.5 Mbps | |
ITU G.992.4 | Splitterless ADSL2 | 1.5 Mbps | 0.5 Mbps | 2002-07 |
ITU G.992.5 | ADSL2 + | 24 Mbps | 1.216 Mbps | 2003-05 |
ITU G.992.5 Annex A | ADSL2 + over POTS | 24 Mbps | 1.216 Mbps | |
ITU G.992.5 Annex B | ADSL2 + over ISDN | 24 Mbps | 1.216 Mbps | |
ITU G.992.5 Annex M | ADSL2 + | 24 Mbps | 3.5 Mbps | |
ITU G.992.5 Annex L | RE-ADSL2 + | 24 Mbps | 1.5 Mbps |
Name | Common name | Maximum reception (Mbit / s) |
Maximum transmission (Mbit / s) |
---|---|---|---|
ANSI T1.413-1998 Issue 2 | ADSL | 8 | 1.0 |
ITU G.992.1 | ADSL (G.DMT) | 8 | 1.3 |
ITU G.992.1 Annex A | ADSL over POTS | 8 | 1.3 |
ITU G.992.1 Annex B | ADSL over ISDN | 8 | 1.8 |
ITU G.992.2 | ADSL Lite (G.Lite) | 1.5 | 0.5 |
ITU G.992.3 | ADSL2 | 12 | 1.0 |
ITU G.992.3 Annex J | ADSL2 | 13 | 3.15 |
ITU G.992.3 Annex L | RE-ADSL2 | 5 | 0.8 |
ITU G.992.4 | splitterless ADSL2 | 1.5 | 0.5 |
ITU G.992.5 | ADSL2 + | 24 | 1.0 |
ITU G.992.5 Annex M | ADSL2 + M | 24 | 3.5 |
The VDSL or VHDSL (of the abbreviations in English Very High-bit-rate Digital Suscriber Line or Line of Subscriber Digital of very high rate of Transfer) is a type of connection to Internet by Broadband of very superior performance to the ADSL , representing its evolution or superior step.
This technology consists of the use of four channels for the transmission of data : two for the download and two for the load, substantially increasing the transmission power of the service.
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