3Com 10014299 manual Schematic diagram of the custom queuing

684CHAPTER 49: CONGESTION MANAGEMENT

rate and throughput rate can be guaranteed to a certain extent in case of network congestion.

The key service (such as ERP) data packets may be put into the higher priority queue, while the non-key service (such as E-Mail) data packets are put into the lower priority queue, so that the data packets of the non-key service are transmitted in the idle intervals during the processing of the key service data. In this way, the priority of the key service is guaranteed and network resources are optimized. However, it brings the problem that the data packets in the lower priority queue may be blocked in the packet queue of the transmission interface for a long period because of the existence of the data packets in the higher priority queue.

Custom Queuing (CQ) As shown in Figure 220, custom queuing (CQ) divides the data packets into 17 classifications (corresponding to 17 queues of CQ) according a given policy, and data packets are input respective CQ queues based on their own classifications following the FIFO policy. In 17 queues of CQ, the queue 0 is the system queue, and queues 1 to 16 are the user queues. The users can configure the proportional relationship of the occupied interface bandwidth between various user queues. When dispatching the queue, the data packets in the system queue are first transmitted. Before the system queue is empty, a certain number of data packets from user queues 1 to 16 are not extracted and sent out according to the predetermined configured proportion using polling method.

Figure 220 Schematic diagram of the custom queuing

i ncomi ng packet s

cl assi f yi ng

queue1	10%
queue2	30%

¡- ¡- queue15 10%

queue16 5%

out goi ng packet s

int er f ace

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PQ assigns the absolute priority to the data packets with higher priority compared to data packets with the lower priority level. In this way, though the priority transmission of the key service data can be guaranteed, when a number of data packets with higher priority need to be transmitted, all bandwidths may be occupied, causing the data packets with lower priority to be completely blocked. With the use of CQ, such a case can be avoided. CQ has total of 7 queues. Queue 0 is the system queue that is first dispatched, and the queues 1 to 16 are the user queues that are dispatched by a polling method based on the bandwidth settings. The users may configure the proportional relationship of the occupied bandwidth between the queues and the enqueuing policy of the packets. Thus, the data packets of various services can be provided with different bandwidths, to guarantee that the key services can be provided with more bandwidth. In addition, it is not likely that non-key services may not be allocated with the bandwidth.