Operation Manual – QoS-QoS ProfileH3C S3100 Series Ethernet Switches Chapter 1 QoS Configuration1-141.3.7 Queue SchedulingWhen the network is congested, the problem that many packets compete for resourcesmust be solved, usually through queue scheduling.In the following section, strict priority (SP) queues, weighted round robin (WRR), andHQ-WRR (High Queue-WRR) queues are introduced.1) SP queuingFigure 1-7 Diagram for SP queuingSP queue-scheduling algorithm is specially designed for critical service applications.An important feature of critical services is that they demand preferential service incongestion in order to reduce the response delay. Assume that there are four outputqueues on the port and the preferential queue classifies the four output queues on theport into four classes, which are queue 3, queue 2, queue 1, and queue 0. Theirpriorities decrease in order.In queue scheduling, SP sends packets in the queue with higher priority strictlyfollowing the priority order from high to low. When the queue with higher priority isempty, packets in the queue with lower priority are sent. You can put critical servicepackets into the queues with higher priority and put non-critical service (such as e-mail)packets into the queues with lower priority. In this case, critical service packets are sentpreferentially and non-critical service packets are sent when critical service groups arenot sent.The disadvantage of SP queue is that: if there are packets in the queues with higherpriority for a long time in congestion, the packets in the queues with lower priority will be“starved” because they are not served.2) WRR queuing