R3721-F3210-F3171-HP High-End Firewalls Network Management Configuration Guide-6PW101

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Congestion management
Causes, impacts, and countermeasures of congestion
Congestion occurs on a link or node when traffic size is so large that the processing capability of the link
or node is exceeded. It is typical of a statistical multiplexing network and can be caused by link failure,
insufficient resources, and various other causes. Figure 171 sh
ow
s two common congestion scenarios:
Figure 171 Typical traffic congestion scenarios
Congestion may bring these 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 technology used for congestion management. It classifies traffic into queues and
picks out packets from each queue following a certain algorithm. The device provides various queuing
algorithms, 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.
1. FIFO