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Configuration Guide - Low Latency Network

CloudEngine 8800, 7800, 6800, and 5800 V200R005C00

This document describes the configurations of Buffer optimization of lossless queues, Fast ECN, Fast CNP, Dynamic ECN threshold of lossless queues, and Dynamic load balancing.
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Differentiated Scheduling for Elephant and Mice Flows in Lossless Queues

Differentiated Scheduling for Elephant and Mice Flows in Lossless Queues


Only the CE6865EI supports this function.


A switch has eight queues numbered from 0 to 7 on each interface in the outbound direction. The higher the queue number, the higher the priority. Typically, the device performs PQ scheduling on packets in different queues according to the queue priority, and forwards the packets in the same queue according to the first in first out (FIFO) policy.

The parameters, for example, packet rate or length, for identifying packets in queues have different values. Packets with values higher than those of packet identification parameters are elephant flows, and packets with values lower than those of packet identification parameters are mice flows.

In Figure 2-2, both elephant and mice flows are transmitted in a lossless queue. When the queue is congested, the queue delay of the mice flows increases because the elephant flows increase the length of the queue. As a result, the Flow Completion Time (FCT) of delay-sensitive mice flows increases greatly. In severe scenarios, when a queue is blocked by elephant flows, packets of mice flows are discarded due to the failure to enter the queue.

Figure 2-2 Packets of delay-sensitive services discarded due to elephant flows

Differentiated scheduling for elephant and mice flows in lossless queues can address the preceding problem. This function allows the device to identify elephant and mice flows in queues based on the flow identification parameters. The device preferentially schedules packets in mice flows to prevent the delay of mice flows from being affected by elephant flows, ensuring the FCT of mice flows.


In Figure 2-3, after the differentiated scheduling is enabled for elephant and mice flows in lossless queues, the device processes the packets in queues as follows:
  1. The device records the packet information in lossless queues in flow table entries, and identifies elephant flows based on the flow table entries and elephant flow identification parameters.
  2. Then the device forwards the identified elephant flows in low-priority queues and forwards the mice flows in high-priority queues.
  3. If the subsequent packets that enter a queue are elephant flows that have been identified, the packets are forwarded in low-priority queues. For other flows, the device repeats the preceding steps.
Figure 2-3 Implementation of differentiated scheduling for elephant and mice flows in lossless queues
Updated: 2019-04-20

Document ID: EDOC1100040243

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