Patent ID: 7761597

Claim:
An address translator to be coupled to a first network conforming to a first addressing system, and to be coupled to a second network conforming to a second addressing system, said address translator comprising: a processor; an address translating unit which translates, in a Layer 3 region of communication data, a Layer 3 address of the first addressing system into a Layer 3 address of the second addressing system, or translates, in a Layer 3 region of communication data, a Layer 3 address of the second addressing system into a Layer 3 address of the first addressing system; a detecting unit which detects that the communication data conforms to a particular protocol based on a port number contained in a header corresponding to a Layer 4 region of the communication data; and a creating unit which creates translation information including a correspondence relationship between the Layer 3 address of the first addressing system and the Layer 3 address of the second addressing system for translating a Layer 3 address contained in a region of the communication data higher than the Layer 3 region, when the detecting unit detects that the communication data conforms to the particular protocol, wherein the address translator further comprises a communication function for communicating with a server device, wherein said address translator sends said translation information and the region of the communication data higher than the Layer 3 region to said server device, and receives information including said Layer 3 address described in the region of the communication data higher than the Layer 3 region which has been translated by said server device, and wherein at least a portion of the region of the communication data higher than the Layer 3 region is described by Session Initiation Protocol (SIP) and includes the Layer 3 address.