ADSL

ADSL is a asymmetric Internet transmission over a telephone line (Asymmetric Digital Subscriber Line). It requires a subscription at a ISP. Based on a DSL asymmetric (transfer speed PC - Internet is lower than the Internet to the PC), this technology provides high-speed digital connections over the telephone network, while allowing to use the phone at the same time.

A telephone line connects to a specific central ADSL modem user, creating three information channels:

• channel high-speed Internet for download (Internet to user)
• an Internet channel duplex average upload speed (transmission to Internet users)
• channel telephone (voice) in the region of 4 kHz

For that, the bandwidth of a telephone line is divided into three parts using the multiplexing frequency division (FDM) but also echo cancellation. To enable call while surfing, plus modem or router Specifically, it is necessary to install a special filter (splitter) That filters the way telephone signals - digital signal.

Two versions of modems / routers are available in annex A allows use on standard lines, annex B is used for lines ISDN.

ADSL allows for a maximum loop length of 5.6 kilometers, providing speeds:

• 1.5 to 2 Mb / s (max. 8 Mbps) minimum in the direction switch to user
• 16 kb / s minimum (max 640kbps) towards user to concentrator

In Belgium, the transfer rate is 4 Mb / s standard download (1 Mb / s if the user is the mileage limit). The France offers speeds of 256 Kbps, 512 Kbps, ... following the subscription. This technology is replaced by the ADSL2, 2 + and VDSL asymmetric. The ReADSL is similar but with a greater distance at the expense of speed.

These speeds depend on the length of the loop, the section of cable and telephone interference.

Definitions Annexes: HDSL 2 and HDSL - SDSL - RADSL - shdsl