queuing algorithm addresses a particular network traffic problem and which algorithm is used affects
bandwidth resource assignment, delay, and jitter significantly.
The Switch 4500G series support the following four queue scheduling methods:
Scheduling all queues with the strict priority (SP) algorithm.
Scheduling all queues with the weighted round robin (WRR) algorithm.
Scheduling all queues with the weighted fair queuing (WFQ) algorithm
Scheduling some queues with the SP algorithm and some with the WRR algorithm.
This section describes how SP, WRR, WFQ, and SP+WRR work in details.
SP queuing is specially designed for mission-critical applications, which require preferential service to
reduce the response delay when congestion occurs.
Figure 5-2 Schematic diagram for SP queuing
As shown in
5-2, SP queuing classifies eight queues on a port into eight classes, numbered 7 to
0 in descending priority order.
SP queuing schedules the eight queues strictly according to the descending order of priority. It sends
packets in the queue with the highest priority first. When the queue with the highest priority is empty, it
sends packets in the queue with the second highest priority, and so on. Thus, you can assign
mission-critical packets to the high priority queue to ensure that they are always served first and
common service packets to the low priority queues and transmitted when the high priority queues are
The disadvantage of SP queuing is that packets in the lower priority queues cannot be transmitted if
there are packets in the higher priority queues. This may cause lower priority traffic to starve to death.
WRR queuing schedules all the queues in turn to ensure that every queue can be served for a certain
time, as shown in