ADSL stands for Asymmetric Digital Subscriber Line. ADSL is a type of DSL line and is one of the technologies vying to replace ISDN. It consists of the transmission of digital data supported by the symmetric pair of copper carried by the conventional telephone line or subscriber line, as long as the range does not exceed 5.5 km measured from the Telephone System, or there are no other services on the same cable that may interfere. It is a broadband Internet access technology, which implies a higher rate of data transmission in the data transfer, and supports simultaneous Internet browsing and phone use.
Through the use of two modems, one installed on the subscriber, the other on the subscriber line, in front of the main distribution, it can significantly improve network throughput and get 70 transmissions times faster than a conventional analogue modem. It achieved by modulating the data signals in a higher frequency band than that used in conventional telephone conversations (300-3800 Hz), a function performed by the ADSL Router. To avoid distortions in the transmitted signals, it is necessary to install a filter (called splitter or discriminator) that is responsible for separating the conventional telephone signal from the modulated signals of the connection using ADSL. This technology called asymmetric because the download capacity (from the Network to the user) and data upload (in the opposite direction) do not match. Usually, the capacity for download is higher than that of upload.
In an ADSL line, three communication channels established, which are data transmission, data reception and standard telephone service. In various countries (such as Spain), telephone companies are implementing improved versions of this technology such as ADSL2 and ADSL2 + with high-quality television and video supply capacity by the telephone pair. Which means stiff competition between telephone operators and of cable, and the appearance of integrated offers of voice, data and television, from the same line and within a single company, that offers these three communication services. The use of higher bandwidth for these services further limits the distance at which the thread pair can operate.
ADSL presents a series of advantages and also some disadvantages concerning the telephone connection to the Internet through a MODEM.
It offers the possibility of talking on the phone while surfing the Internet, since, as indicated above, voice and data work in separate bands, which implies separate channels. Use an existing infrastructure (the first telephone network). It is advantageous, both for operators who do not have to face significant expenses for the implementation of this technology, and for users, since the cost and time they take to have the service available is less than if the operator had to undertake works to generate new infrastructure.
ADSL users have a permanent connection to the Internet since they do not have to establish this connection through dialling or signalling to the network. It is possible because there is a point-to-point connection, so the line between the exchange and the user is not shared, which also guarantees a bandwidth dedicated to each user, and increases the quality of the service. It is comparable to a switched network architecture. It offers a connection data transmission rate much higher than that obtained by dialling the Internet. It is the most exciting aspect for users. The possibility of using IP telephony for long-distance calls (before too expensive), makes the basic telephone service currently offered by the operators as an added service, rather than the primary use, offering flat rates for its use. In some countries, there is no possibility to register the ADSL regardless of the landline.
Not all telephone lines can offer this service, because the demands of torque quality, both noise and attenuation, by distance to the exchange, are more stringent than for the basic telephone service. The theoretical limit for an acceptable service is equivalent to 5 km. Due to the care that these lines require, the service is not economical in countries with few or lousy infrastructure, especially if we compare it with prices in other countries with more advanced infrastructure. The router needed to connect, or failing that, the ADSL modem, is expensive (to a lesser extent in the case of the modem). However, in some countries, it is common for ISPs (Internet Service Provided) to include the cost of both devices in the price of the service.
A telephone line is required for its operation, although it can be used to make calls. The ADSL router is a device that allows you to connect one or several computers or even a local area network (LAN) to the Internet through a telephone line with an ADSL service; it is several components in one. Next, I point out the functions of the ADSL Router: Router: when a packet arrives from the Internet, it directs it to the destination interface by the corresponding path, that is, it is capable of routing IP packets. ADSL Modem: modulates the signals sent from the local network so that they can be transmitted over the ADSL line and demodulates the signals received by it so that the LAN equipment can interpret them. Configurations are consisting of an ADSL modem and a router that perform the same function as an ADSL router. Wireless access point:
Some manufacturers of this technology are: Asus, 2Wire, 3Com, Alcatel, Cisco, Comtrend, D-Link, Huawei, Linksys, Nokia, Netgear, Xavi, Thomson, U.S. Robotics, Zyxel, Air-Link, Encore, Supergrass and Kozumi. Some ADSL routers allow communication via wireless (without cables) with local network equipment.