ADSL is an asymmetric version of DSL, which uses digital coding technology to obtain the maximum data transmission capacity from the existing copper telephone line without interfering with the conventional voice service on the same line. The reason is that it uses frequencies other than telephone voice transmission to transmit data. Users can make phone calls or send faxes while surfing the Internet, which will not affect the call quality or slow down the speed of downloading Internet content. ADSL uses slightly different protocols according to the different ways of accessing the Internet. Of course, no matter what protocol ADSL uses, it is based on the most basic protocol TCP/IP and supports all TCP/IP program applications.

Bridging access mode

ADSL access relies on ATM backbone network and inherits the characteristics and advantages of many ATM technologies at the access end. Therefore, various standards for carrying data packets on ATM networks are naturally adopted by ADSL access technology, making ADSL bridge access mode the most basic form of ADSL broadband access at present.

Traditional IP access mode

The internationally popular RFC 1577 standard is a standard specification for carrying IP protocols on ATM networks. In the protocol, it is clear that the standard is only for the IP protocol of the network layer, and the communication between them is realized by IP routing and forwarding, so it is also called IPoverATM. To realize ADSL broadband access of RFC 1577, user terminals need expensive ATM network cards and drivers supporting this protocol, which greatly limits the popularization and use of RFC 1577 in ADSL access.

PPPoverATM access mode

IETF has formulated a standard specification -pppovertm for broadband dial-up access using PPP technology. However, user terminals need additional network devices and corresponding drivers, which makes it difficult to popularize and apply them on a large scale.

Point-to-point tunneling technology to PPPoA access mode

The implementation of this access mode on the network side is completely in line with PPPoA. The difference is that it can realize PPTP access by using the virtual private network adapter that comes with the existing WIN98/NT operating system, and it is very practical without purchasing other equipment. However, the protocol stack of this access mode is too complex, which greatly reduces the actual access rate of users and can hardly realize VOD services with high bandwidth and high quality requirements.

PPPoE access mode

IETF formulated the technical specification of PPPoE in 1998. It uses PPP technology to directly realize higher speed, more reliable and more convenient ADSL broadband access, and combines the existing broadband access server with local Ethernet. Considering the hardware requirements of user terminals, the overall performance of ADSL broadband access is improved. Therefore, the completion of PPPoE technical specifications has been widely supported, and now it has become the preferred broadband access mode for broadband access operators.

PPPoE is based on two widely accepted standards: LAN Ethernet and PPP point-to-point dialing protocol. For end users, it is not necessary to understand the deep LAN technology, but just as ordinary dial-up Internet access. For service providers, there is no need to spend a lot of money on large-scale transformation on the basis of the existing network, and set up IP address binding user support private line mode. This makes PPPoE more advantageous than other protocols in broadband access services, so it has gradually become the best choice for broadband Internet access. PPPoE software plays a very important role in the system. Its function is to connect PPP protocol and Ethernet protocol of operating system, and connect ISP through PPPoE protocol.