3Com SuperStack 4, Configuration Manual

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214 C
HAPTER
8: ACL C
ONFIGURATION
Figure 50 SP
The SP is designed for the key service application. A significant feature of the key
service is the need for priority to enjoy the service to reduce the responding delay
when congestion occurs. Take 8 egress queues for each port as an example, SP
divides the queue of the port into up to 8 kinds, from high-priority queue to
low-priority queue (which are shown as the Queue 7, 6, 5, 4, 3, 2, 1 and 0 in turn)
with sequentially reduced priority.
During the progress of queue dispatching, strictly following the priority order from
high to low, the SP gives preference to and sends the packets in the higher-priority
queue first. When the higher-priority queue is empty it will send the packets in the
lower-priority group. In this way, put the packets of higher priority service in the
higher-priority queue and put the packets of lower priority, like e-mail, in the
lower-priority queue, can guarantee the key service packets of higher priority are
transmitted first, while the packets of lower service priority are transmitted during
the idling gap between transmitting the packets of higher service priorities.
Note that SP has the drawback that when congestion occurs, if there are many
packets queuing in the higher-priority queue, it will require a long time to transmit
these packets of higher service priority while the messages in the lower-priority
queue are continuously set aside without service.
Traffic Mirroring
The traffic mirroring function is carried out by copying the specified data packets
to the monitoring port for network diagnosis and troubleshooting.
Traffic Counting
With the flow-based traffic counting, you can request a traffic count to count and
analyze the packets.
Packets sent via this
interface
high priority
Low priority
Classify
Packets sent
Sending queue Dequeue
queue 7
queue 6
queue 5
queue 4
queue 3
queue 2
queue 1
queue 0