Buffer management is one of the important and difficult problems in high performance routers and switches.One excellent buffer management scheme can improve the resource utilization and decrease the number of discard packets.We first discuss some buffer management schemes and algorithms oriented to fixed length cells with dynamic thresholds-DT and Optimal DT

and DT for multiple loss priorities.Then we put forward the optimal DT for multiple loss priorities that can be applied in high performance routers and simulate it orienting to varying-length packets.It receives the advantage of full use of buffer

owned by the Optimal DT

with fewer number of discard packets in the case of multiple priorities

and the simulation analysis indicates that its performance is quite excellent.