Countermeasure; Traffic Control Technologies - 3Com 3C13636 Configuration Manual

3Com Router 3000 Ethernet Family
Configuration Guide
Impact
Congestion may cause the following negative effects:
Increase the delay and jitter of packet transmission
Packet re-transmission caused by high delay
Decrease the efficient throughput of network and waste the 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.

1.4.2 Countermeasure

A direct way to solve resources deficient problem is to increase the bandwidth of
network; however, it cannot resolve all the problems concerning congestion.
A more effective method to solve the problem of QoS is to enhance the functions of
traffic control and resource allocation at network layer, 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.

1.5 Traffic Control Technologies

Traffic classification, traffic policing, traffic shaping, congestion management,
congestion avoidance, and physical-interface LR 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 router.
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 policing 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.
3Com Corporation
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Chapter 1 QoS Overview