Method for transmitting facsimile data between facsimile apparatuses through an internet protocol network and relay apparatuses used in the method

1. Field of the Invention A method for transmitting facsimile data between facsimile apparatuses each connected to a relay apparatus, and relay apparatuses being connected each other through an internet protocol network, includes steps of: performing an address conversion from a telephone number of a facsimile apparatus of the reception side to an IP address corresponding to the telephone number; transmitting a request for TCP connection to a relay apparatus corresponding to a destination of the IP address when receiving an identifying signal which indicates transmission of the facsimile data from the facsimile apparatus of the sending side; and transmitting the facsimile data to the relay apparatus corresponding to the destination of the IP address based on the TCP connection.