©1999 IEEE VESIT Student Branch Hits :
Webauthor : Saumitra M Das
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ADSL - KEDAR A. DHURU Fr.C.R.E.
The competition between the Cable TV and Telephone may be paying its dividends in the near future for the home Internet user, as telephone companies around the world start with something called Digital Subscriber Lines (DSL). By turning your Telephone line into a digital connection, DSL allows a user to connect to the Internet at speeds which would normally require dedicated fibre-optic lines.The most common type of DSL is ADSL (Asymmetric DSL), converts existing twisted-pair technologies into access paths for multimedia and high speed data communication. The ADSL technology modifies your telephone line, enabling you to enjoy the benefits of high speed data transfer and a normal telephonic conversation over the same pair of twisted cables. The high speed data communication can be of two types: the high speed downstream channel and a medium speed duplex channel, depending upon the implementation of the ADSL architecture. The high speed data transfer ranged from 1.5-6 Mbps (Mega-Bits per second) and the duplex rates range from 16-640 Kbps(Kilo-bits per second). ADSL is an asymmetric protocol and was originally designed to deliver far more data than a user could send, in fact, it was designed to deliver video signals over a telephone line. Development of the web has shown that it too is asymmetric in the sense that users download far more data than they send. The speeds that this system can give you depends upon the proximity to your local telephone exchange and it doesn’t work more than 6000m away from a telephone exchange. The other factors on which speed of an ADSL connection depends are: Wire-gauge, presence of bridged gaps and cross-couple interference. Attenuation increases with length and frequency and decreases as diameter decreases. ADSL will perform as follows:
Technology: The new generation of signal processors used in ADSL are powerful integrated circuits designed to handle complex Analog-to-Digital conversions, as well as analysing and manipulating analog signals. This allows an ADSL modem to directly convert a stream of digital data into a large number of separate analog channels, operating at different frequencies and data rates to take advantage of all the available bandwidth of a telephone line. This discrete Multi-tone technology is designed to adapt to changes in the telephone line, due to temperature, or interference due to other calls and lines. To create multiple channels, ASL modems divide the available band-width of a telephone line in one of two ways: Frequency Division Multiplexing or Echo Cancellation. FDM assigns one band for upstream data and one band for downstream data. The downstream path is then divided by Time Division Multiplexing into one or more high speed channels and one or more downstream channels. Echo Cancellation assigns the upstream band to overlap the downstream band and separates the two by means of local echo cancellation. An ADSL modem organises the total data stream created by multiplexing downstream channels, duplex channels and maintenance channels together into blocks, and attaches an error correction code to each block. The receiver then corrects the errors that occur during transmission. Thus, we see that with ADSL technology we can get uploading or downloading speeds in excess of 640 Kbps. The downloading, or one way transfer, speeds can go as high as 6 Mbps, So, are the days of the conventional modems numbered? The answer to this will only be known when ADSL lines have been successfully tested.
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©1999 IEEE VESIT Student Branch Hits :
Webauthor : Saumitra M Das |