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AR Router Troubleshooting Guide

This Product Documentation provides guidance for maintaining AR Enterprise Router, covering common information collection and fault diagnostic commands, typical fault troubleshooting guide, and troubleshooting.
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Huawei uses machine translation combined with human proofreading to translate this document to different languages in order to help you better understand the content of this document. Note: Even the most advanced machine translation cannot match the quality of professional translators. Huawei shall not bear any responsibility for translation accuracy and it is recommended that you refer to the English document (a link for which has been provided).
How Are Packets Discarded After Congestion Avoidance Is Configured?

How Are Packets Discarded After Congestion Avoidance Is Configured?

Congestion avoidance configured on devices uses the Weighted Random Early Detection (WRED) mechanism, which defines different drop policies for packets of different services. WRED discards packets based on packet priorities, so the drop probability of packets with higher priorities is low. In addition, WRED randomly discards packets so that rates of TCP connections are reduced at different times. This prevents global TCP synchronization.

WRED defines upper and lower threshold for the length of each queue. The packet drop policy is as follows:

  • When the length of a queue is shorter than the lower threshold, no packet is discarded.

  • When the length of a queue exceeds the upper threshold, all received packets are discarded.

  • When the length of a queue ranges from the lower threshold to the upper threshold, incoming packets are discarded randomly. RED generates a random number for each incoming packet and compares it with the drop probability of the current queue. If the random number is greater than the drop probability, the packet is discarded. A longer queue indicates a higher drop probability.

Updated: 2019-08-09

Document ID: EDOC1000079719

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