2-10Figure 2-9 Line rate implementationWith a token bucket used for traffic control, when there are tokens in the token bucket, the burstypackets can be transmitted; if no tokens are available, packets cannot be transmitted until new tokensare generated in the token bucket. In this way, the traffic rate is restricted to the rate for generatingtokens, thus limiting traffic rate and allowing bursty traffic.Priority MappingConceptsWhen a packet enters a network, it is marked with a certain priority to indicate its scheduling weight orforwarding priority. Then, the intermediate nodes in the network process the packet according to thepriority.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).z For more information about 802.1p precedence, DSCP values, and IP precedence, refer to PacketPrecedences.z Local precedence is a locally significant precedence that the device assigns to a packet. A localprecedence value corresponds to an output queue. Packets with the highest local precedence areprocessed preferentially.The device provides two priority trust modes on a port:z Trust packet priority: the device assigns to the packet the priority parameters corresponding to thepacket’s priority from the mapping table.z Trust port priority: the device assigns a priority to a packet by mapping the priority of the receivingport.You can select one priority trust mode as needed. Figure 2-10 shows the process of priority mapping ona device.
