Abstract: In a networking method of a communication apparatus in which global address information and port information are acquired on a network, a virtual private network is established with another communication apparatus using the global address information and the port information to perform the communication, the networking method includes determining whether communication data that is transmitted from the communication apparatus is a first protocol or a second protocol, and starting a data transmission through the network before the virtual private network is established when the communication apparatus determines that the communication data is the first protocol, and starting a data transmission after the virtual private network is established when the communication apparatus determines that the communication data is the second protocol.

Abstract: In a NAT type determination method pursuant to RFC 3489, address information added in a binding response from a STUN server in response to a binding request issued in a latest transmission test is compared with address information added in a binding response in response to any transmission test executed therebefore. When the address information are not identical, a NAT type is determined symmetric. Even when a router whose NAT type changes frequently according to a use status is connected, communication is capable without manual setting change by a user.

Abstract: In a NAT type determination method pursuant to RFC 3489, address information added in a binding response from a STUN server in response to a binding request issued in a latest transmission test is compared with address information added in a binding response in response to any transmission test executed therebefore. When the address information are not identical, a NAT type is determined symmetric. Even when a router whose NAT type changes frequently according to a use status is connected, communication is capable without manual setting change by a user.