3Com Switch 4500 26-Port Configuration Manual page 139

Packet Filter
Packet filter is used to filter traffic. For example, the operation "deny" discards the
traffic that is matched with a traffic classification rule, while allowing other traffic
to pass through. With the complex traffic classification rules, the Switch enables
the filtering of various information carried in Layer 2 traffic to discard the useless,
unreliable or doubtful traffic, thereby enhancing network security.
The two key steps of realizing the frame filtering are as follows.
1 Classify the ingress traffic according to the classification rule;
2 Filter the classified traffic, that is, the "deny" operation, the default ACL
operation.
Traffic Policing
To deliver better service with the limited network resources, QoS monitors the
traffic of the specific user on the ingress, so that it can make a better use of the
assigned resource.
Port Traffic Limit
The port traffic limit is the port-based traffic limit used for limiting the general
speed of packet output on the port.
Traffic Priority
The Ethernet Switch can deliver priority tag service for some special packets. The
tags include TOS, DSCP and 802.1p, etc., which can be used and defined in
different QoS modules.
Queue Scheduling
When congestion occurs, several packets will compete for the resources. The
queue scheduling algorithm is used to overcome the problem.
Weighted Round Robin (WRR)
Round scheduling ensures every queue is given some service time on the Switch
port. Take 4 egress queues for each port as an example, WRR gives each queue a
weight (w3, w2, w1, and w0 respectively) for obtain resource. For example, you
can configure the weight value of the WRR algorithm for 100M port as 50, 30, 10,
10 (corresponding to the w3, w2, w1 and w0 respectively). Therefore, the
low-priority queue can be guaranteed to get the minimum bandwidth of 10Mbps,
avoiding the case in SP scheduling that the messages in the lower-priority queues
may not get any service for some time. Another advantage of the WRR queue is
that the service time is assigned to each queue flexibly, although it is the round
multiple queue scheduling. When a queue is empty, it will switch to the next
queue immediately, thereby making good use of the bandwidth resource.
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.
QoS Configuration 137