3Com Switch 8800 Advanced Software V5 Configuration Guide

Traffic Management Technologies 829
■ Increase the delay and jitter of packet transmission
■ Packet re-transmission caused by high delay
■ Decrease the efficient throughput of network and lower the utilization of
network resources
■ Intensified congestion can occupy too many network resources (especially in
memory), and the irrational assignment of resources even can lead to resource
block and breakdown for the system
It is obvious that congestion will make the traffics unable to obtain the resources
in time and degrade the service performance accordingly. No one wants
congestion, but it occurs frequently in complex environments where packet
switching and multi-users applications coexist. So it needs to be treated cautiously.
Countermeasure A direct way to solve resources deficiency problem is to increase the bandwidth of
network; however, it cannot resolve all the problems caused by congestion.
A more effective method to solve the problem of QoS is to enhance the functions
of traffic control and resource allocation in the network, and to provide
differentiated services for applications with different service requirement in order
to allocate and use resources rightly. During the process of resources allocation
and traffic control, the direct or indirect factors that might cause network
congestion should be controlled with best effort to reduce the probability of
congestion. As congestion occurs, resource allocation should be balanced
according to features and demands of applications, to minimize the effects on
QoS by congestion.
Traffic Management
Technologies
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:
■ Traffic classification: It is a prerequisite for differentiated service, to identify the
interested objects based on a certain matching rule.
■ Traffic policing: polices the specification of particular traffics entering the
switch. When the traffics exceed the specification, then some restriction or
punishment measures can be taken to protect the commercial benefits of
carriers and to prevent network resources from being damaged.
■ Traffic shaping: A traffic control measure of actively adjusting the output speed
of traffics, generally it can enable the traffic to adapt to the network resources
supplied by the downstream switch, to prevent the unwanted packet dropping
and congestion. Same as traffic policing, traffic shaping is implemented at the
IP layer.
■ Congestion management: handles resource competition during network
congestion. Generally, it stores the packets in the queue first, and then takes a
dispatching algorithm to assign the forwarding sequence of packets.
■ Congestion avoidance: Exceeding congestion consumes network resources.
Congestion avoidance can monitor the usage status of network resources, and
as congestion becomes worse, actively take the policy of dropping packets
through adjusting traffic to resolve the overloading of the network.