Dynamic thresholds buffer management in a shared buffer packet switch paper summary

In this section , We described PSPP Specific ideas of the plan . First , We divide output ports into active ports and inactive ports . If the output port i The queue length of is greater than the average buffer size , namely B/W , Then output port i Called active port ; Otherwise, it is called an inactive port . B Is the total buffer size ,N Is the number of output ports . For inactive ports ,PSPP The operation of is similar to CS, It is called partial sharing (PS) buffer . For active ports ,PSPP Is similar to CP, It is called partial partition (PP) buffer . PS The size of the buffer is determined according to the following criteria ： First, all inactive ports should be allocated enough PS Buffer to provide fair access ; The other is PS The size of the buffer should be as small as possible , In order to allocate more buffer space to the active port to reduce packet loss . therefore , How to determine the PS The size of the buffer is important for improving faimes And the overall loss of performance is very important .

Suppose at time t Assigned to all inactive ports PS The buffer size is given by the following formula ,

：PSPP Threshold factor

：t Number of inactive ports at any time .

：t Cache allocated to all inactive ports at any time .

If in t The number of incoming packets sent to all inactive ports at any time is greater than , Then discard the redundant packets ; otherwise , Allow these packets to enter PS buffer . PS After the buffer size is determined ,PSPP Calculate the cache control threshold for each active port , namely PP Buffer size . hypothesis t The control threshold of time is T(t), Then the following formula can be given ,

 

 ：t Set of inactive ports at the moment .

：t Time output port i The queue length of .

  If , It's in t When the time has arrived, go to the active port i Packets of will be discarded . Incoming packets destined for this active port will be discarded , Until the queue length is below the control threshold T(t) or T(t) Rise above the queue length ,PSPP It can dynamically adapt to traffic changes . Whenever the traffic load changes significantly , The system will experience a transient . for example , When an inactive port suddenly starts to get cache space , Its queue length and total cache occupancy will increase , Cause the control threshold to decrease . If the queue length exceeds the control threshold , Then all incoming packets will be temporarily blocked when they are discharged , This frees up more buffers for new active ports . After stabilization , All active ports , Whether old or new , Will have the same queue length .

When referring to steady-state symbols , We just need to delete the time parameter from all variables t. for example ,Qi Indicates active port i Maximum allowable queue length ,T Express T(t) Steady state value of . If there is S Inactive ports , So we can get T As follows ：

  here Express S Shared cache of inactive port requests .