1-17
1) SP
queuing
Figure 1-8
Diagram for SP queuing
SP queuing is specially designed for mission-critical applications. The key feature of
mission-critical applications is that they require preferential service to reduce the
response delay when congestion occurs. Assume that there are eight output queues on
the port and SP queuing classifies the eight output queues on the port into eight classes,
which are queue 7, queue 6, queue 5, queue 4, queue 3, queue 2, queue 1, and queue
0 in the descending order of priority.
SP queuing schedules the eight queues strictly in 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. By assigning mission-critical packets to high priority queues and common
service packets to low priority queues, you can ensure that the mission-critical packets
are always served prior to common service packets.
The disadvantage of SP queuing is that packets in the lower priority queues cannot get
served if there are packets in the higher priority queues for a long time when congestion
occurs. This may cause low priority traffic to starve to death.
2) WRR
queuing
