3Com Switch 7750 Configuration Guide Guide

Overview 619
■ Modify the precedence and forward: Modify the priority of the packets whose
evaluation result is "partly-conforming" and forward them.
■ Enter the next-rank policing: TP can be piled up rank by rank and each rank
polices more detailed objects.
Redirect You can re-specify the forwarding port of packets as required by your own QoS
policy.
Queue Scheduling When the network is congested, the problem that many packets compete for
resources must be solved, usually in the way of queue scheduling.
In the following section, strict priority (SP) queues and weighted round robin
(WRR) queues are introduced.
1 SP queue
Figure 160 Diagram for SP queues
SP queue-scheduling algorithm is specially designed for critical service
applications. An important feature of critical services is that they demand
preferential service in congestion in order to reduce the response delay. Assume
that there are 8 output queues on the port and the preferential queue classifies
the 8 output queues on the port into 8 classes, which are queue7, queue6,
queue5, queue4, queue3, queue2, queue1, and queue0. Their priorities decrease
in order.
In the queue scheduling, SP sends packets in the queue with higher priority strictly
following the priority order from high to low. When the queue with higher priority
is empty, packets in the queue with lower priority are sent. You can put critical
service packets 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 sent preferentially and non-critical service packets are sent
when critical service groups are not sent.
Packets sent via this
interface
high priority
Low priority
Classify
Packets sent
Sending queueDequeue
queue 7
queue 6
queue 5
queue 4
queue 3
queue 2
queue 1
queue 0
Packets sent via this
interface
high priority
Low priority
Classify
Packets sent
Sending queueDequeue
queue 7
Packets sent via this
interface
high priority
Low priority
Classify
Packets sent
Sending queueDequeue
queue 7
queue 6
queue 5
queue 4
queue 3
queue 2
queue 1
queue 0