DSL (Digital Subscriber Line) is technology enhances the data capacity of existing twisted-pair wire that runs between the local telephone company switching offices & most homes. While the wire itself can handle higher frequencies, the telephone switching equipments is designed to cut off signals above 4,000 Hz to filter noise off the voice line, but now everybody is searching for ways to get more bandwidth to improve access to the Web hence DSL technologies.
There are actually 7 types of DSL service, ranging in speeds from 16 Kbits/sec to 52 Mbits/sec. The services are either symmetrical (traffic flows at the same speed in both direction), or asymmetrical (the downstream capacity is higher than upstream capacity). Asymmetrical services (ADSL) are suitable for Internet users because more information is usually downladed. For example, a simple button click in a web browser can start an extended download that includes graphics and text.As data rates increase, the carrying distance decrease. That means that users who are beyond a certain distancefrom the telephone company's central office may not be able to obtain the higher speeds.
A DSL connection is a point-to-point dediated circuit,meaning that the link is always up and there is no dialing required.
ADSL is an asymmetrical technology, meaning that the downstream data rate is much higher than the up stream data rate. As mentioned, for example, from Web servers, than is uploaded. ADSL operates in frequency range that is above the frequency of voice services, so the two systems can operate over the same cable.
The best ISP companies that offer DSL/ADSL in Egypt are:
2-Link Dot Net