Abstract: In this paper,the cell loss rate and maximum throughput of an internal nonblocking backpressure input and output ATM switch under burst traffic is investigated.The arrival process to each input port is on-off (active and silence)cell stream with geometrical distribution.In each time slot within active period,a cell is generated with certain probability p,and the silence period may be zero slot.Cells belonging to the same burst are directed to the same output port,while bursts are addressed uniformly among the switch output ports.The length of input/output beffers is finite,and switch speed -up factors arbitray.The comprehensive understanding is also given to realize an input/output backpressure packet switch.