The present invention relates to a packet transfer apparatus for connecting terminals to destination communication networks by using PPPoE (Point to Point Protocol over Ethernet) (Ethernet is a registered trademark).
The communication networks (IP networks) using IP (Internet Protocol) have become widely used, and created various communication services such as Web access (the so-called Internet), file transfer (data transfer), VoIP (IP phone) and multicast (broadcast). In a communication system widely employed for offering these communication services, packet transfer apparatuses that properly process the received IP packets (hereinafter, occasionally simply called the packets) to be suited for communication and transfer them are provided between a network (the so-called access network provided by a carrier) that holds the ends of user's terminals that enjoy the communication services and other networks (the networks managed/provided by service providers or carriers to run communication services, respectively) that offers the communication services so that the packets from the terminals can be transferred through the packet transfer apparatuses to the facilities (servers) of the communication service providers.
In the access network provided between the user terminals and the packet transfer apparatuses, PPPoE is generally employed to assure the safety (security) and reliability of the packets to be transmitted and received. That is, according to PPPoE, a PPP session is established by using a protocol called PPP on Ethernet (a registered trade name, and hereinafter the same) that is defined in PFC2516 of IETF, and then packets are distributed (transferred).
This PPPoE is used to establish a PPP session on the Ethernet (in the access network) between the packet transfer apparatus and the user terminals so that the packets can be transferred as if they were transferred on exclusive lines. The sequence using the protocol for the transfer of packets is started with the broadcast transmission of a start packet called PADI (The PPPoE Active Discovery Initiation) from a terminal toward the packet transfer apparatuses in order to search for a packet transfer apparatus that could accept a desired communication service. The packet transfer apparatus that can accept the requested communication service (or can transfer the packet to the corresponding communication service provider) transmits a PADO (The PPPoE Active Discovery Offer) packet back to this terminal. Then, this terminal transmits a PADR (The PPPoE Active Discovery Request) packet for requesting to start a PPP session back to the specified packet transfer apparatus. The corresponding packet transfer apparatus allocates a unique session ID to the terminal, and sends a confirmation packet called PADS (The PPPoE Active Discovery Session-Confirmation) back to the terminal. In this case, the session ID is included in the PADS sent from the packet transfer apparatus, and used for the packet transfer apparatus to identify the terminal that has received the PADS. After the establishment of PPP session, the packet transfer using PPP is performed by using this session ID.
According to RFC2516, the terminals side can specify within the PADI packet the Service-Name that indicates the type of the requested communication service and the TAG length that indicates the length of the Service-Name. Examples of the Service-Name are Web access (Internet) and IP (IP phone). In the current RFC2516, however, when the Service-Name is not specified in the parameter of PADI packet, the TAG length of the Service-Name is regarded as 0. In addition, the PADI packet in which the TAG length of the Service-Name is 0 can be accepted by any network service such as the Internet (the PADO packet is transmitted back).