PPPoE (Ethernet-based PPP) provides services for connecting remote access devices through simple bridges. Under this model, each user host uses its own PPP stack, the user uses the familiar interface. Access control, billing, service type, etc. can be performed for each user, not every site.
In order to provide a point-to-point connection on an Ethernet, each PPP session must know the remote communication of the other party's Ethernet address and establish a unique session identifier. PPPoE contains an Ethernet address discovery protocol to provide this feature.
PPPOE is divided into two phases, namely the discovery address discovery phase and the PPP session phase. When a host wants to initiate a PPPoE session, it must first perform discovery to determine the other party's Ethernet MAC address and establish a PPPoE session identifier session_id. Although PPP is defined by end-to-end peer-to-peer relationship, Discovery is a naturally-server relationship. During discovery, the host (as client) discovers an access concentrator (Access Concentrator as a server), depending on the topology of the network, maybe the host can communicate with more than one access. The discovery phase allows the host to discover all access concentrators and select one from it. When the discovery phase is successfully completed, both hosts and access concentrs have all the information needed to establish a point-to-point connection on Ethernet.
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