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Configuration Guide - QoS

CloudEngine 8800, 7800, 6800, and 5800 V200R002C50

This document describes the configurations of QoS functions, including MQC, priority mapping, traffic policing, traffic shaping, interface-based rate limiting, congestion avoidance, congestion management, packet filtering, redirection, traffic statistics, and ACL-based simplified traffic policy.
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Overview of Congestion Monitoring and Analysis

Overview of Congestion Monitoring and Analysis

When network congestion occurs, congestion monitoring and analysis of network devices help you to learn information about packets that cause congestion and provide guidance to planning and adjusting network traffic.

Congestion Monitoring and Analysis

On an enterprise network, congestion mainly affects network performance and results in problems such as transmission delay and signal loss. In addition, due to rapid increase of traffic in data centers, data center switches need to display device usage in a fine-granular manner. The network-wide management and maintenance efficiency is therefore improved.

The device supports millisecond-level monitoring and analysis for each queue of an interface. The device can display the buffer usage of each queue and information about packets that cause congestion in real time, providing guidance to planning and adjusting network traffic.

Basic Concepts

Queue

A queue is used to schedule packets and limit the bandwidth of an interface, and each queue has a buffer space. When the device is congested, the device places packets into the buffer space of queues and uses a scheduling algorithm to determine the packet forwarding sequence.

Buffer threshold
A buffer threshold is used to measure the queue buffer usage. There are upper and lower buffer thresholds:
  • When queue-based congestion monitoring is enabled and the buffer usage is higher than or equal to the lower buffer threshold, the device records historical congestion monitoring information.
  • When interface-based congestion analysis is enabled and the buffer usage is higher than or equal to the upper buffer threshold, the device records congestion analysis information.

By default, the lower buffer threshold is 5% of the queue buffer space and the upper buffer threshold is 90% of the queue buffer space. Upper and lower buffer thresholds can be configured manually.

Implementation

Congestion Monitoring
Queue-based congestion monitoring enables the device to continuously read the buffer usage of queues and to record the usage as real-time congestion monitoring information. In addition, the device compares the read queue buffer usage with the lower buffer threshold:
  • If the read queue buffer usage is lower than the lower buffer threshold, the device does not save the read buffer usage.
  • If the read queue buffer usage is higher than or equal to the lower buffer threshold, the device saves the read buffer usage as historical information about congestion monitoring.
NOTE:
  • The device saves a maximum of 100 pieces of historical congestion monitoring information for each queue.
  • The accuracy between two pieces of historical congestion monitoring information for the same queue is within 2 ms.
  • All historical congestion monitoring information can be saved for a maximum of 30s.

When congestion occurs on the device, you can check historical information about congestion monitoring saved on the device to learn the buffer usage of each queue.

Congestion Analysis

Interface-based congestion analysis enables the device to compare the read queue buffer usage with the higher buffer threshold. If the buffer usage of any queue on an interface is higher than or equal to the higher buffer threshold, the device obtains and analyzes packets on the interface and saves the analysis result (Ethernet field and 5-tuple of packets).

When congestion occurs on the device, you can check saved packet analysis results to learn packet congestion information.

NOTE:
  • Congestion analysis can be enabled on only one interface of the device.
  • The device sorts analysis results based on the proportion of congested packets and displays only 10 types of the most congested packets.
  • The device saves only the packet analysis result for the congestion that occurred last time.
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Updated: 2019-03-21

Document ID: EDOC1000166640

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