Asymmetric Digital Subscriber Line - ADSL

ADSL is a technique for asymmetric broadband access networks and the Internet. ADSL is a variant of DSL. This technique is used to transfer data at frequencies greater than 25 kHz, which are not used for voice calls. The asymmetry here lies in the fact that the transmission of data from the network to the user is faster than in the other way. This technology has been developed for users who more often receive data (e.g. from web pages) than send data (e.g. having a web server). This standard uses ordinary copper telephone lines. ADSL allows to achieve much higher throughput than the modem telephone technology, in which all signals are transmitted in the band reserved for voice. In the most common case of Plain Old Telephone Service at the phone signal is demodulated into digital form with 8 bit encoding at 8 kHz frequency, what corresponds to 64 kbps capacity. Broadband data and phone call are transmitted via common cable, so they have to be separated in end points by filter (splitter). The data signal is routed to ADSL modem and the panel discussion is directed to the ordinary telephone network. Data packets associated with the transmission bandwidth are transmitted through the DSLAM or to internal ATM network (telecommunication service provider then uses PPPoA) [1] or Ethernet network to service provider (when PPPoE encapsulation is used) until the Internet gateway. ADSL provides transmission speeds of 16 kbps to 24 Mbps. The speed with which you can send data, is usually much lower. ADSL technology is described in ITU-T G.992.1, G.992.2 (G.Lite) (and subsequent) and ANSI T1.413-1998 standard. ADSL1 is the oldest version of the technology which allows for data transmission at a speed of 1536 kbps or 2048 kbps, at a distance up to 5.5 km. The bandwidth can be maximized up to 8192 kbps, but only for short telephone lines (no longer than 2.7 km).


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