ATL Telecom R1-SW Ethernet Switch - Manual (Page 182)

R1-SW24L2B User’s Manual
9-14
Drop Probability
1
0 Queue Size
Max Size
Buffer Manager
Queues of an output port have fixed size. If a queue is full of packets, and other packets flow
into the queue, the packets are discarded as a particular rule. Buffer manager is the function
that discards received packets selectively to solve the congestion of the queue.
This section introduces that buffer manager methods.
Tail Drop
In Tail drop method, if there is no space to store
packets, packets that arrived after full of the queue
are discarded. The ratio that packets are discarded
is ‘1’ when the amount of packet in the queue
becomes the size of the queue (Max Size) as the
right graph.
Retransmission requests are sent to senders
continuously because packets are discarded after
the queue is full. The host that received retransmission requests considers that the link is not
stable and makes transmission speed slow. If this situation occurs repetitively, the speed of
whole network is slower. This problem is called TCP global synchronization.