PPPoE Protocol definition and features

Next, we will introduce the content of the PPPoE protocol. First, we need to understand the basic concepts of the PPPoE protocol. The PPPoE protocol (PPP over Ethernet) is used to establish PPP connections over Ethernet. Due to the mature and widely used Ethernet technology, in traditional dial-up Internet applications, the PPP protocol shows good scalability and excellent management and control mechanisms. The PPPoE protocol combined with the two has been recognized and widely used by broadband access operators.

PPPoE not only features fast and simple Ethernet, but also powerful PPP functions. Any protocol that can be encapsulated by PPP can be transmitted through PPPoE.

The PPPoE establishment process can be divided into the Discovery phase and the PPP session phase. The Discovery stage is a stateless stage. In this stage, the access server is selected to determine the Session ID of the PPP Session to be established and obtain the peer point-to-point connection information; standard PPP processes are implemented in the PPP session phase.

A typical Discovery stage involves the following four steps:

(1) The host first actively sends the broadcast package PADI to find the access server. PADI must contain at least one service name TAG to indicate the services required by the host.

(2) If the access server can provide host requirements after receiving the package

(3) The host selects an appropriate access server in response to PADO and sends a PADR notification to the Access Server. The PADR must declare the service type requested to the access server.

(4) After receiving the PADR package, the access server allocates a unique Session identifier Session ID to the user, starts the PPP state machine to prepare for starting the PPP Session, and sends a Session Validation Package PADS.

After receiving the PADS, the host enters the PPP session phase. In the Session phase, the Ethernet domain of PPPoE protocol is set to 0x8864, the CODE is 0x00, and the Session ID must be the value assigned by the Discovery stage.

The PPP session phase mainly involves the negotiation process of LCP, authentication, and NCP protocols. The LCP phase mainly completes the establishment, configuration, and detection of data link connections, the authentication protocol type is negotiated by LCP (CHAP or PAP). NCP is a protocol family used to configure different network layer protocols. IP Control Protocol (IPCP) is commonly used ), it is responsible for configuring the user's IP address and DNS.

The PADT package is a session stop package. It can be initiated by either party of the session, but must be valid after the session is established.

PPPoE features

PPPoE not only features fast and simple Ethernet, but also powerful PPP features. Any protocol that can be encapsulated by PPP can be transmitted through PPPoE. In addition, PPPoE has the following features:

(1) PPPoE can easily check that the user is offline. You can collect statistics on the user's duration or traffic through the establishment and release of a PPP session. The billing method is flexible and convenient.

(2) PPPoE provides a dynamic IP Address Allocation Method. You do not need to configure any IP addresses, and the network management is easy to maintain. You can solve the IP address shortage problem without adding devices, it can well locate users' activities on this website.

(3) users can access the Internet by entering their usernames and passwords through free PPPoE client software (such as EnterNet), similar to the traditional dial-up Internet access, which maximizes the user habits, from the operator's perspective, PPPoE has made minor changes to its existing network structure.

DSLAM is an ADSL aggregation device. Its kernel uses an ATM or IP address, but the uplink port is an Ethernet port. BAS is the access server that implements the PPPoE function at the local end and ends the PPPoE process initiated by the user side. Downlink Ethernet frames are sent from the IP Man to the BAS through routers. After the PPPoE header is added, the Ethernet frames are sent to the DSLAM and encapsulated into AAL5 frames. the downlink Ethernet frames are sent to the ADSL Modem through the crossover module, the AAL5 frame is restructured and the Ethernet frame is sent to the client. The client extracts the IP packet from the PPPoE package.

The upstream PPPoE package is encapsulated into AAL5 frames in the ADSL Modem, which is transmitted by the ATM cell to the local DSLAM. The DSLAM is responsible for terminating the ATM and re-assembling the PPPoE package, and transmit it to BAS for processing through the set PVC (permanent virtual circuit.

From the above, we can see that the PPPoE Protocol carries PPP over Ethernet, which provides a logical point-to-point link on the network of the shared media. for users, the ATM Transmission Between DSLAM and ADSL Modem is transparent. If you replace the DSLAM and ADSL Modem in the middle with the access device of the cable TV, it is a typical type of access device of the HFCs, BAS does not change the PPPoE package processing method.