∙Mean rate—The rate at which tokens are put into the bucket (the permitted average rate of traffic). It is usually set to the committed information rate (CIR).

∙Burst size—The capacity of the token bucket (the maximum traffic size that is 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 corresponding 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.

How line rate works

With line rate configured on an interface, all packets to be sent out the interface are firstly handled by the token bucket of line rate. If enough tokens are available in the token bucket, 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.

a.Line rate implementation

With a token bucket used for traffic control, when tokens are available in the token bucket, the bursty packets can be transmitted; if 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, limiting traffic rate and allowing bursty traffic.

Priority mapping

What is priority mapping

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 precedence, DSCP values, IP precedence, and local precedence).

∙For more information about 802.1p precedence, DSCP values, and IP precedence, see Packet precedences.

∙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.

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