Patent ID: 8611253

Claim:
A transmitting apparatus comprising: a user input unit configured to receive a user input; a communication interface configured to transmit a check packet to a receiving apparatus using Transfer Control Protocol (TCP), the check packet including a random number that is different from random numbers included in other check packets transmitted from the transmitting apparatus; and circuitry configured to: receive a TCP acknowledgement message to the check packet from the receiving apparatus, the TCP acknowledgement message including acknowledgement information based on shared data shared with the receiving apparatus; compute expected acknowledgment information based on the shared data shared with the receiving apparatus; produce a comparison result for the receiving apparatus based on the acknowledgment information and the expected acknowledgment information; count a time elapsed from transmitting the check packet; and prohibit transmission of data to the receiving apparatus when the comparison result indicates that acknowledgment information and the expected acknowledgment information do not match or when a predetermined time elapsed from transmitting the check packet expires before the acknowledgment message is received.