55Custom queuingFigure 13 Custom queuing (CQ)CQ organizes packets into 16 classes (corresponding to 16 queues) by certain matchcriteria. A certain class of packets enters the corresponding custom queue according toFIFO queuing. Queues 1 through 16 are customer queues, as shown in Figure 13 . Youcan define match criteria and assign a percentage of interface bandwidth for each ofthese 16 customer queues. By default, packets are assigned to queue 1.During a cycle of queue scheduling, CQ first empties the system queue. Then, itschedules the 16 customer queues in a round robin way: it sends a certain number ofpackets (based on the percentage of interface bandwidth assigned for each queue)out of each queue in the ascending order of queue 1 to queue 16. CQ guaranteesnormal packets of a certain amount of bandwidth, while ensuring that mission-criticalpackets are assigned more bandwidth.CQ can assign free bandwidth of idle queues to busy queues. Even though it performsround robin queue scheduling, CQ does no assign fixed time slots for the queues. If aqueue is empty, CQ immediately moves to the next queue. When a class does not havepackets, the bandwidth for other classes increases.Congestion management technology comparisonBreaking through the single congestion management policy of FIFO for traditional IPdevices, the current AC provides all the congestion management technologies above
