H3C Technologies H3C SR8800 - Manual (Page 47)

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Configuring hardware congestion
management
Congestion management overview
Causes, impacts, and countermeasures of congestion
Congestion occurs on a link or node when traffic size exceeds the processing capability of the link or
node. It is typical of a statistical multiplexing network and can be caused by link failures, insufficient
resources, and various other causes. Figure 15 shows some common congestion scenarios.
Figure 15 Traffic congestion causes
Congestion can bring the following negative results:
• Increased delay and jitter during packet transmission
• Decreased network throughput and resource use efficiency
• Network resource (memory in particular) exhaustion and even system breakdown
Congestion is unavoidable in switched networks or multi-user application environments. To improve the
service performance of your network, you must take measures to manage and control it.
One major issue that congestion management deals with is how to define a resource dispatching policy
to prioritize packets for forwarding when congestion occurs.
Congestion management policies
Queuing is a common congestion management technique. It classifies traffic into queues and picks out
packets from each queue by using a certain algorithm. Various queuing algorithms are available, each
addressing a particular network traffic problem. Your choice of algorithm affects bandwidth assignment,
delay, and jitter significantly.
Congestion management involves queue creating, traffic classification, packet enqueuing, and queue
scheduling. Queue scheduling treats packets with different priorities differently to transmit high-priority
packets preferentially.
Several common queue-scheduling mechanisms are introduced here.