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Backpressure refers to the buildup of data at an I/O switch when buffers are full and not able to receive additional data. No additional data packets are transferred until the bottleneck of data has been eliminated or the buffer has been emptied.
To create backpressure, the I/O switch must broadcast false collision detection signals or return data packets to their originator.
Protocols are written to deal with such conditions at a node, in this case at a switch. For example, Ethernet uses carrier sense multiple access/collision detection (CSMA/CD). This is an internationally standardized protocol called a contention protocol, which determines how network devices respond to backpressure. It also determines when two devices attempt to use the same channel (a signal medium such as a wire or fiber optic cable) simultaneously without being multiplexed. CSMA/CD is standardized in IEEE 802.3 and ISO 8802.3.
All participating stations detect the backpressure or data packet collisions. After a predetermined time interval, the transmitting stations will again attempt to transmit. If the collisions are again detected, the time interval before data transmission is increased, and then increased incrementally each time the problem is detected. This process is called exponential back-off.