If the number of data packets in a network exceeds a certain value, then the network becomes overloaded and its performance decreases. This is the case when the buffer in the receiving data station
overflows and the storage space for buffering becomes scarce. Due to congestion, the network needs more time
tohandle and remove congestion situations, congestion and conflicts. Congestion controls, congestion control, avoid such bottlenecks.
Congestion controls should be implemented in a distributed manner or even moved to subnets. Such control mechanisms ensure that sufficient storage capacity
fordata buffering is available at the transition points between the subnets.
One possibility of congestion control is the reservation of buffer memories, other procedures work with flow control and control the data flow via a window technique, and still other procedures are based on the rejection of data packets as soon as the buffer memory is full. The latter method for overload control is called retransmission method. It has the disadvantage that the network is additionally loaded by the rejected data packets.