3Com Switch 4210 9-Port, Configuration Manual

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300 C
HAPTER
28: Q
O
S C
ONFIGURATION
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.
Major Traffic Control
Techniques
Traffic identifying, traffic policing (TP), traffic shaping (TS), congestion
management, and congestion avoidance are the foundations for a network to
provide differentiated services. Mainly they implement the following functions.
■
Traffic identifying identifies specific packets based on certain matching rules. It
is a prerequisite for differentiated service.
■
TP 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.
■
TS 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.
■
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.
■
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 identifying is the basis of all the above-mentioned traffic management
technologies. It identifies packets using certain rules and makes differentiated
services possible. TP, TS, congestion management, and congestion avoidance are
methods for implementing network traffic control and network resource
management. They are occurrences of differentiated services.
QoS Supported By
Switch 4210 Family
Traffic Identifying Traffic here refers to service traffic; that is, all the packets passing the switch.
Traffic identifying means identifying packets that conform to certain characteristics
according to certain rules. It is the foundation for providing differentiated services.
In traffic identifying, 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 identifying 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 identifying is done by checking
the information carried in packet header. Packet payload is rarely adopted for
traffic identifying. The identifying rule is unlimited in range. It can be a quintuplet