Communication apparatus, communication system and communication method

摘要

The NAT type of a router can be examined by communicating with one server having one IP address, and a P2P communication path is established efficiently using the NAT type obtained by the examination. A terminal 100 transmits a plurality of port number examination request packets having a plurality of port numbers of a server 001 set as the destination port. The terminal 100 refers to a port number examination response packet received from the server 001 to acquire a plurality of port numbers obtained by address translation by a router 101 for the port number examination request packets respectively. The terminal 100 determines the NAT type of the router 101 based on the acquired translated port numbers. The terminals 100 and 200 establish a P2P communication path efficiently using the determined NAT type.