H3C Technologies H3C SecPath F1000-E - Manual (Page 512)

4
Figure 2 Typical traffic congestion scenarios
100M>10M
（100M+10M+50M）>100M
100M
100M
100M
50M
10M 10M
（1） （2）
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. There are 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.
FIFO
Figure 3 FIFO queuing
Packets to be sent
through this interface Packets sent
Sending queue
Queue Interface
As shown in
Figure 3 , First In First Out (FIFO) uses a single queue and thus does not classify traffic or
schedule queues. FIFO delivers packets depending on their arrival order, with the one arriving earlier
scheduled first. The only concern of FIFO is queue length, which affects delay and packet loss rate. On