Priority Marking; Traffic Policing - 3Com E4500-24 Cli Configuration Manual

Priority Marking

The priority marking function is to reassign priority for the traffic matching an ACL referenced for traffic
classification.
If 802.1p priority marking is configured, the traffic will be mapped to the local precedence
corresponding to the re-marked 802.1p priority and assigned to the output queue corresponding to
the local precedence.
If local precedence marking is configured, the traffic will be assigned to the output queue
corresponding to the re-marked local precedence.
If IP precedence or DSCP marking is configured, the traffic will be marked with new IP precedence
or DSCP precedence.

Traffic Policing

The network will be made more congested by plenty of continuous burst packets if the traffic of each
user is not limited. The traffic of each user must be limited in order to make better use of the limited
network resources and provide better service for more users. For example, traffic can be limited to get
only its committed resources during a time period to avoid network congestion caused by excessive
bursts.
Traffic policing is a kind of traffic control policy used to limit the traffic and the resource occupied by
supervising the traffic. The regulation policy is implemented according to the evaluation result on the
premise of knowing whether the traffic exceeds the specification when traffic policing is performed.
Normally, token bucket is used for traffic evaluation.
Token bucket
The token bucket can be considered as a container with a certain capacity to hold tokens. The system
puts tokens into the bucket at the set rate. When the token bucket is full, the extra tokens will overflow
and the number of tokens in the bucket stops increasing.
Figure 1-5 Evaluate the traffic with the token bucket
Packets to be sent
through this port
classification
Evaluating the traffic with the token bucket
When token bucket is used for traffic evaluation, the number of the tokens in the token bucket
determines the amount of the packets that can be forwarded. If the number of tokens in the bucket is
Put tokens in the bucket at the
set rate
Packet
Token
bucket
Drop
Continue
to send
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