Data communication system and method with improved system efficiency

A data communications system, comprising:

• a central control unit;
• a plurality of terminals;
• and
• a communication channel having an upstream channel and a downstream channel, the communication channel connecting the central control unit and the terminals, the upstream channel being time-shared among the terminals and a time-shared channel being assigned to a terminal that requests a time-shared channel;
• wherein the central control unit comprises:
• means for sending a first packet to at least one of the terminals;
• means for detecting an arrival of a second packet sent by the one terminal in response to the first packet;
• means for measuring a round-trip time from the sending to the detecting;
• means for selecting the longest round-trip time among a plurality of measured round-trip times;
• means for updating the longest round-trip time at predetermined intervals after the selecting the longest round-trip time;
• and
• means for controlling the timing of data transmission of the central control unit according to the longest round-trip time.

A method for controlling a data communications system having a central control unit, a plurality of terminals, and a communication channel having an upstream channel and a downstream channel, the communication channel connecting the central control unit and the terminals, the upstream channel being time-shared among the terminals and a time-shared channel being assigned to a terminal that requests a time-shared channel comprising the steps of:

• assigning a time-shared channel to a terminal that requests a time-shared channel;
• sending a first packet to one of the terminals;
• detecting an arrival of a second packet sent by the one terminal in response to the first packet;
• measuring a round-trip time from the sending to the detecting;
• selecting the longest round-trip time among a plurality of measured round-trip times;
• updating the longest round-trip time at predetermined intervals after the selecting the longest round-trip time;
• and
• controlling the timing of data transmission of the central control unit according to the longest round-trip time.