Patent ID: 7746852

Claim:
A packet data serving node for connecting a communication terminal device to a public network by using Point to Point Protocol (PPP), the packet data serving node supporting a plurality of layer 3 protocol types, comprising: Link Control Protocol (LCP) phase processing means; Network Control Protocol (NCP) phase processing means; decision means for deciding a layer 3 protocol type of a reception PPP packet; and control means, wherein, when performing a PPP connection in a NCP phase after an LCP phase is completed, the control means controls the NCP phase processing means not to transmit any NCP start request message to the communication terminal device before receiving a NCP start request message from the communication terminal device, the decision means receives the NCP start request message from the communication terminal device, and refers to a protocol field in the received NCP start request message to decide the layer 3 protocol type used by the communication terminal device, and the control means controls the NCP phase processing means to transmit a NCP connection permission message set corresponding to the layer 3 protocol type decided by the decision means and a NCP start request message of the layer 3 protocol type decided by the decision means to the communication terminal device.