US Patent 7330426 Receiver-based RTT measurement in TCP

A method of performing Round Trip Time (RTT) measurement in a data packet receiver using a Transmission Control Protocol (TCP) for communication via a network with a sender, said method comprising the steps of sending an acknowledgement for a currently received data packet to the sender, measuring a first time instant when sending the acknowledgement, triggering at the sender the transmission of an expected data-packet, measuring a second time instant when the expected data packet is received, and calculating the round-trip time based on the measured first and second time instants.