HP FlexNetwork NJ5000, User Manual

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Burst size
—The capacity of the token bucket, or the maximum traffic size permitted in each
burst. It is usually set to the committed burst size (CBS). The set burst size must be greater than
the maximum packet size.
One evaluation is performed on each arriving packet. In each evaluation, if the number of tokens in
the bucket is enough, the traffic conforms to the specification and the tokens for forwarding the
packet are taken away. If the number of tokens in the bucket is not enough, it means that too many
tokens have been used and the traffic is excessive.
Working mechanism of rate limit
With rate limit configured on an interface, all packets to be sent through the interface are firstly
handled by the token bucket of rate limit. If the token bucket has enough tokens, packets can be
forwarded. Otherwise, packets are put into QoS queues for congestion management. In this way, the
traffic passing the physical interface is controlled.
Figure 444 Rate limit implementation
With a token bucket used for traffic control, when the token bucket has tokens, the bursty packets
can be transmitted. When no tokens are available, packets cannot be transmitted until new tokens
are generated in the token bucket. In this way, the traffic rate is restricted to the rate for generating
tokens, the traffic rate is limited, and bursty traffic is allowed.
Priority mapping
Concepts
When a packet enters a network, it is marked with a certain priority to indicate its scheduling weight
or forwarding priority. Then, the intermediate nodes in the network process the packet according to
the priority.
When a packet enters a device, the device assigns to the packet a set of predefined parameters
(including the 802.1p priority, DSCP values, and local precedence).
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For more information about 802.1p priority and DSCP values, see " Packet precedences ."
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Local precedence is a locally significant precedence that the device assigns to a packet. A local
precedence value corresponds to an output queue. Packets with the highest local precedence
are processed preferentially.
The device provides the following priority trust modes on a port:
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Trust packet priority
—The device assigns to the packet the priority parameters corresponding
to the packet's priority from the mapping table.