ZyXEL P-870HN-51b User Guide - Page 213
Token Bucket
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Chapter 16 Quality of Service (QoS) Table 76 Internal Layer2 and Layer3 QoS Mapping LAYER 2 LAYER 3 PRIORITY QUEUE 6 IEEE 802.1P USER PRIORITY (ETHERNET PRIORITY) 6 TOS (IP PRECEDENCE) DSCP 4 100110 100100 100010 100000 5 101110 7 7 101000 6 110000 7 111000 IP PACKET LENGTH (BYTE) Token Bucket The token bucket algorithm uses tokens in a bucket to control when traffic can be transmitted. The bucket stores tokens, each of which represents one byte. The algorithm allows bursts of up to b bytes which is also the bucket size, so the bucket can hold up to b tokens. Tokens are generated and added into the bucket at a constant rate. The following shows how tokens work with packets: • A packet can be transmitted if the number of tokens in the bucket is equal to or greater than the size of the packet (in bytes). • After a packet is transmitted, a number of tokens corresponding to the packet size is removed from the bucket. • If there are no tokens in the bucket, the Device stops transmitting until enough tokens are generated. • If not enough tokens are available, the Device treats the packet in either one of the following ways: In traffic shaping: • Holds it in the queue until enough tokens are available in the bucket. In traffic policing: • Drops it. • Transmits it but adds a DSCP mark. The Device may drop these marked packets if the network is overloaded. Configure the bucket size to be equal to or less than the amount of the bandwidth that the interface can support. It does not help if you set it to a bucket size over the interface's capability. The smaller the bucket size, the lower the data transmission rate and that may cause outgoing packets to be dropped. A larger P-870HN-5xb User's Guide 213