3com WX3000 Manuel D’Utilisation

 

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Video-on-Demand (VoD). Enterprise users expect to connect their regional branches together using 

VPN techniques for coping with daily business, for instance, accessing databases or manage remote 

equipments through Telnet.  

All these new applications have one thing in common, that is, they have special requirements for 

bandwidth, delay, and jitter. For instance, bandwidth, delay, and jitter are critical for videoconference 

and VoD. As for other applications, such as transaction processing and Telnet, although bandwidth is 

not as critical, a too long delay may cause unexpected results. That is, they need to get serviced in time 

even if congestion occurs.  

Newly emerging applications demand higher service performance from IP networks. In addition to 

simply delivering packets to their destinations, better network services are demanded, such as 

allocating dedicated bandwidth, reducing packet loss ratio, avoiding congestion, regulating network 

traffic, and setting priority of the packets. To meet those requirements, the network should be provided 

with better service capability.  

Traffic classification, traffic policing, traffic shaping, congestion management, and congestion 

avoidance are the foundations for a network to provide differentiated services. Mainly they implement 

the following functions. 

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Traffic classification identifies specific packets based on certain matching rules. It is a prerequisite 

for differentiated service.  

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Traffic policing confines traffics to a specific specification. You can configure restriction or 

punishment measures against the traffics exceeding the specification to protect the benefits of 

carriers and to prevent network resources from being abused.  

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Traffic shaping actively adjusts the output rate of traffics. It can enable the traffics to match the 

capacity of the downstream network devices, so as to prevent packets from being dropped and 

network congestion.  

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Congestion management handles resource competition during network congestion. Generally, it 

adds packets to queues first, and then forwards the packets by using a scheduling algorithm.  

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Congestion avoidance monitors the use of network resources and drops packets actively when 

congestion reaches certain degree. It relieves network load by adjusting traffics.  

Traffic classification is the basis of all the above-mentioned traffic management technologies. It 

identifies packets using certain rules and makes differentiated services possible. Traffic policing, traffic 

shaping, congestion management, and congestion avoidance are methods for implementing network 

traffic control and network resource management. They are occurrences of differentiated services.  

Traffic here refers to service traffic; that is, all the packets passing the device. 

Traffic classification means identifying packets that conform to certain characteristics according to 

certain rules. It is the foundation for providing differentiated services.  

In traffic classification, the priority bit in the type of service (ToS) field in IP packet header can be used to 

identify packets of different priorities. The network administrator can also define traffic classification 

policies to identify packets by the combination of source address, destination address, MAC address, IP 

protocol or the port number of an application. Normally, traffic classification is done by checking the