3Com 4800G Series, Configuration Manual

Page: 859 / 1246

Major Traffic Management Techniques 859
■
Aggravated congestion will consume a large amount of network resources
(especially memory resources), and unreasonable resource assignment will even
lead to system resource deadlock and cause the system breakdown.
It is obvious that congestion is the root of service performance declination because
congestion makes traffic unable to get resources timely. However, congestion is
common in a complicated environment where packet switching and multi-user
services coexist. Therefore, congestion must be treated carefully.
Countermeasures Increasing network bandwidth is a direct way to solve the problem of resource
insufficiency, but it cannot solve all the problems that cause network congestion.
A more effective way to solve network congestion problems is to enhance the
function of the network layer in traffic control and resource assignment, to
provide differentiated services for different requirements, and to assign and utilize
resources correctly. In the process of resource assignment and traffic control, the
direct or indirect factors that may cause network congestion must be properly
controlled so as to reduce the probability of congestion. When congestion occurs,
the resource assignment should be balanced according to the features and
requirements of all the services to minimize the influence of congestion on QoS.
Major Traffic
Management
Techniques
Traffic classification, traffic policing (TP), traffic shaping (TS), congestion
management, and congestion avoidance are the foundation for providing
differentiated services. Their main functions are as follows:
■
Traffic classification: Identifies packets according to certain match rules. Traffic
classification is the prerequisite of providing differentiated services.
■
TP: Monitors and controls the specifications of specific traffic entering the
device. When the traffic exceeds the threshold, restrictive or punitive measures
can be taken to protect the business interests and network resources of the
operator from being damaged.
■
Congestion management: Congestion management is necessary for solving
resource competition. Congestion management is generally to cache packets in
the queues and arrange the forwarding sequence of the packets based on a
certain scheduling algorithm.
■
Congestion avoidance: Excessive congestion will impair the network resources.
Congestion avoidance is to supervise the network resource usage. When it is
found that congestion is likely to become worse, the congestion avoidance
mechanism will drop packets and regulate traffic to solve the overload of the
network.
■
TS: TS is a traffic control measure to regulate the output rate of the traffic
actively. TS regulates the traffic to match the network resources that can be
provided by the downstream devices so as to avoid unnecessary packet loss
and congestion.
Among the traffic management techniques, traffic classification is the basis
because it identifies packets according to certain match rules, which is the
prerequisite of providing differentiated services. TP, TS, congestion management,
and congestion avoidance control network traffic and assigned resources from
different approaches, and are the concrete ways of providing differentiated
services.