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3.2.6 QoS
QoS (Quality of Service) is used to evaluate the capability that server meets customer's service
demands. In Internet, what QoS evaluates is the service capability of network forwarding and
packet.
QoS can evaluate from the different aspects according to the various services provided by the
network. QoS evaluates bandwidth, delay, dithering and packet loss during packet and
forwarding.
Congestion
Congestion is common in a complex Internet packet switched environment. See the following
example:
1)
The packet comes in the device by the high-speed link and exits by low-speed link.
2)
The packet comes in the device from multiple ports and exits from one port (The speed
rate of multiple ports larger than that of the exit port).
If the flow arrives at linear speed, it will encounter the resource chock point, and then the
congestion will generate.
Besides the aggression bandwidth, any other resource shortages (such as the shortages of
distributive processing time, buffer and memory resources) will cause congestion. Additionally,
the poor control of the arrived flow in a certain time, which leads to the flow exceeding the
distributive network resource, is also a factor for generating congestion.
3.2.6.1 Port
Through setting CoS, the priority for packet passing egress port of switch can be decided.
If the congestion occurs at the egress port, the switch will give a CoS value to the packet after it
passes the ingress port. The larger the CoS value, the higher the priority.
Step 1
Select Advanced > Seldom-used > QoS > Port Classification.
The Port Classification interface is displayed. See Figure 3-53.
Figure 3-52
Flow congestion
Advanced Settings 46
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