PPPOE protocol entry-level

The dial-up era seems to be far away. With the intervention of broadband, all households can access the Internet. Here, we will introduce the broadband access technology of the PPPOE protocol. Let's see what's special about this technology.

Background of PPPOE Protocol

With the continuous development of broadband network technology, the application of several mainstream broadband access technologies, such as xDSL, CableModem, and Ethernet, has been in full swing. At the same time, it brings various puzzles to major network operators. No matter which access technology is used, what they hope and can find is how to effectively manage users, how to get a return from the network investment is more sensitive to the charging of various broadband access technologies.

In the traditional Ethernet model, we do not have the so-called concept of user billing. Either users can set/obtain IP addresses to access the Internet, or users cannot access the Internet. IETF engineers are using NAS devices to end users' PPP data packets based on the operating philosophy of narrowband dial-up Internet access ), A Protocol for transmitting PPP data packets Over Ethernet is developed ).

After the launch of this protocol, network equipment manufacturers have also launched their own brands of Broadband Access Server BAS). It not only supports the termination of PPPOE protocol data packets, but also supports many other protocols. For example, MA5200 small BAS) and ISN8850 big BAS ).

PPPOE Protocol Introduction

The PPPOE Protocol provides a standard for connecting multiple hosts to a Remote Access Concentrator in a broadcast-type network such as Ethernet. In this network model, we can easily see that all users' hosts must be able to initialize their own PPP protocol stacks independently.

In addition, through some characteristics of the PPP protocol, users can be billed and managed on the broadcast network. In order to establish and maintain the point-to-point relationship between each host and the Access Concentrator on a broadcast network, a unique point-to-point session must be established between each host and the Access Concentrator.

PPPOE protocol consists of two phases: PPPOE Discovery phase PPPOE Discovery Stage) and PPPOE Session Stage ). This training material focuses more on the introduction of the PPPOE discovery phase, because for the PPPOE session phase, we can see that the PPP session process is the same and can directly refer to the PPP protocol training materials ), the main difference between the two is that the PPPOE packet header is encapsulated before the PPP data packets.

Data packets at any stage are eventually encapsulated into Ethernet frames for transmission. When a host wants to start a PPPOE session, it will first say this in the broadcast network protocol, but in actual application, it may also need to jump to a multi-point access network, for example, ATM, which forms a PPPOEOA data packet) to find an Access Concentrator.

Of course, when there may be Multiple Access Concentrator on the network, the host will be based on the Access Concentrator AC, Access Concentration) provide services or pre-configuration of users for selection. After the host selects the required Access Concentrator, it starts to establish a PPPOE session process with the Access Concentrator.

In this process, the Access Concentrator allocates a unique process ID for each PPPOE session. After the session is established, the PPPOE session phase starts, in this phase, the point-to-point structure of the two sides of the point-to-point connection is different from that of the PPP. It is a logical point-to-point relationship.) The PPP protocol is used to exchange data packets, to complete a series of PPP processes, the network layer datagram is finally transmitted on this point-to-point logical channel.

PPPOE protocols include the discovery phase of PPPOE and the session phase of PPPOE. Most BAS broadband access servers support the PPPOE protocol.