Data to be transmitted in a shared channel environment may typically be "packaged" in frames to facilitate transmission. A frame is a set of consecutive time slots in which the position of each digit time slot is identified by reference to a frame-alignment signal. The frame-alignment signal may not necessarily occur entirely or even in part in each frame.
In shared channel environments having simultaneous channel access, two or more devices may transmit a frame simultaneously, causing collisions. Most protocols in use today use a form of random backoff for resolving these collisions. In random backoff, where devices involved in the collision "hear" the collision as it occurs, the collision is resolved by selecting a random number that controls how long, i.e., what timeout period, a device must wait before retransmitting. "Hear" typically means that a device receiver is tuned to the same channel as the transmissions, the device actually receives its own transmission and recognizes that the message is garbled, e.g., signals received do not match signals transmitted and the device implies a collision from the incorrectly received signals. When the timeout period has been completed, the device retransmits. The retransmitted frame may collide again with frame transmissions from the same device(s) involved in the original collision if the other devices select approximately the same amount of time to wait before retransmitting, or with any other device that coincidentally chooses to transmit. When repeated collisions occur while devices are trying to retransmit, the devices back off longer and longer amounts of time, until a maximum number of retransmission attempts has occurred, at which point the frame is dropped. Under heavy channel loading, the probability of multiple collisions of frames occurring increases to the point of congestion collapse, i.e., very little or no frame traffic is transmitted successfully without collisions.
Further, in some environments, only one "headend Master" device can hear the "upstream" transmissions of the "remote Slave" devices, and all remote Slave devices can hear the "downstream" transmissions of the headend Master (e.g., multidrop modem Wide Area Networks (WANs), coaxial cable CATV WANs, etc.). In this type of environment, one solution is for the headend Master to repeat all remote Slave upstream transmissions by transmitting them downstream, so that those involved in a collision can hear the collision. However, this type of solution uses bandwidth that could more profitably be utilized for downstream transmissions when some or all transmissions are sent beyond a local network (e.g., to destinations in a wide area network).
Thus, in shared channel environments where simultaneous channel access can occur, a system and method are needed for efficiently resolving the resulting collisions when two or more Slave devices transmit simultaneously.
USPTO Backgrounds
USPTO Backgrounds