A method of determining a round trip delay time in a network comprising receiving a gate message allocating a transmission time window; retrieving a first timestamp from the gate message; setting a first clock to the time corresponding to the first timestamp, and wherein the first clock runs synchronously with a second clock recovered from a received data stream; sending upstream, after a time interval comprising a grant start time included in the transmission time window offset by a random delay time, a registration request message, wherein the registration request message includes a second timestamp obtained from the first clock; and determining a round trip delay (RTT) from a time the registration request message is received and the second timestamp.