ADSL (Asymmetric Digital Subscriber Loop Asymmetric Digital Subscriber Loop) is a member of xDSL family, which uses copper twisted pair such as ordinary telephone line and class 3/5 line as transmission medium. Because it adopts brand-new digital Modem technology, it can transmit broadband technology with a bandwidth much higher than that of modem and ISDN, and it is the "darling of the century" in the network era.

ADSL can realize broadband service by using ordinary telephone lines. As long as the corresponding ADSL terminal equipment is installed at both ends of the ordinary straight-line telephone, you can enjoy broadband technology. The original ordinary telephone line does not need to be modified, which is convenient to install and use, and avoids the trouble of wiring difficulties and indoor decoration damage caused by line modification.

After installing and using ADSL, the original telephone service has not changed, and the telephone number and service performance of users are exactly the same as before. And you can surf the Internet and make phone calls at the same time on a telephone line, and the two do not interfere with each other.

The bandwidth of ADSL can reach 1 MB/s in the upstream and 8 MB/s in the downstream, which fully meets the bandwidth requirements of all broadband services at present. ADSL's two-way rate asymmetry completely conforms to the business characteristics of users using the Internet-"more downloads and less uploads", which is very suitable for broadband business applications such as high-speed Internet access and video services. However, due to the limitation of uplink rate, ADSL is not suitable for the bidirectional symmetric point-to-point high-speed data transmission application with IMB/S rate.

ADSL network is star-shaped, and users' lines and bandwidth are exclusive, so there will be no situation that the speed inevitably caused by sharing lines and bandwidth with others will be affected by the number of concurrent users. The user's rate and bandwidth remain basically unchanged, which is especially suitable for business applications that need constant rate and bandwidth, such as high-speed data download and video service. Moreover, due to the exclusive characteristics of line and bandwidth, the information between ADSL users is isolated from each other, and users have complete security guarantee.

The information transmission of ADSL is based on ATM cells, and the local equipment of ADSL is connected to ATM backbone network, so ADSL can make full use of the perfect quality assurance mechanism of ATM technology to make the information transmission quality of ADSL users reach the highest level of telecommunications.

ADSL line is "one line for one household" and ADSL equipment is "one set for one household", so each user will not have communication interference due to other people's line and equipment failures. Because there are no * * * lines and equipment, ADSL has the smallest fault range. Also, there are no active or passive devices (such as amplifiers and distributors) on ADSL lines, so the failure rate of ADSL is also the lowest.

The transmission distance of ADSL can reach 3-5 kilometers. According to the current situation of telephone network, 90% users can enjoy the high-quality network service brought by ADSL.

ADSL access modes include private line access mode and virtual dial-up access mode. Private line access mode (that is, static IP mode) means that the telecommunications company assigns a fixed static IP address to users, which is relatively simple to access the Internet; Virtual dial-up access mode (PPPOE dial-up mode) is not to dial the telephone number, and the cost has nothing to do with the telephone service. Instead, the user enters the account number and password and obtains a dynamic IP address through authentication. Users need to install PPPOE dial-up client software in their computers.