Operation Manual – QoS
H3C S3610&S5510 Series Ethernet Switches
Chapter 1 QoS Overview
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within a certain period of time is improperly controlled and the traffic goes beyond the
assignable network resources.
1.4.2 Influence of Congestion
Congestion may cause a series of negative influences:
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Congestion increases delay and delay jitter in packet delivery.
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Excessively high delay will cause retransmission of packets.
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Congestion decreases the effective throughput of the network and the utilization of
the network resources.
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Aggravated congestion will consume a large amount of network resources
(especially memory resources), and unreasonable resource assignment will even
lead to system resource deadlock and cause the system breakdown.
It is obvious that congestion is the root of service performance declination because
congestion makes traffic unable to get resources timely. However, congestion is
common in a complicated environment where packet switching and multi-user services
coexist. Therefore, congestion must be treated carefully.
1.4.3 Countermeasures
Increasing network bandwidth is a direct way to solve the problem of resource
insufficiency, but it cannot solve all the problems that cause network congestion.
A more effective way to solve network congestion problems is to enhance the function
of the network layer in traffic control and resource assignment, to provide differentiated
services for different requirements, and to assign and utilize resources correctly. In the
process of resource assignment and traffic control, the direct or indirect factors that
may cause network congestion must be properly controlled so as to reduce the
probability of congestion. When congestion occurs, the resource assignment should be
balanced according to the features and requirements of all the services to minimize the
influence of congestion on QoS.
1.5 Major Traffic Management Techniques
Traffic classification, traffic policing (TP), traffic shaping (TS), congestion management,
and congestion avoidance are the foundation for providing differentiated services. Their
main functions are as follows:
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Traffic classification: Identifies packets according to certain match rules. Traffic
classification is the prerequisite of providing differentiated services.
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TP: Monitors and controls the specifications of specific traffic entering the device.
When the traffic exceeds the threshold, restrictive or punitive measures can be
taken to protect the business interests and network resources of the operator from
being damaged.
