3Com CoreBuilder 9000, Руководство пользователя

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16
T
RAFFIC
M
ANAGEMENT
This chapter describes traffic management in the CoreBuilder
®
9000 ATM
Enterprise Switch. The following topics are discussed:
Traffic Management Basics
Traffic Management in the CoreBuilder 9000 ATM Enterprise Switch
Traffic
Management Basics
ATM technology supports a wide variety of services and applications.
Each type of application, whether it be voice, video, or data, has its own
special transmission performance requirements such as delay sensitivity
and information loss tolerance. These requirements are expressed in a set
of parameters called
Quality of Service (QoS) which includes such factors
as permissible transmission delay, delay variation, and cell loss ratio. An
important task of the ATM network is to provide the appropriate QoS
requirements for each application it is carrying. Traffic Management on
the ATM network protects the network and the end-system from
congestion to achieve network performance objectives. An additional
role of Traffic Management is to promote the efficient use of network
resources. Finally, Traffic Management allows the devices to transmit over
a broader bandwidth for longer periods of time, making the network
more efficient.
Control Methods Different methods support Traffic Management. Many of them work on a
closed-loop feedback control principle, where congestion is sensed at
some point in the network and a control signal is sent back to limit the
traffic at its source.
The CoreBuilder 9000 ATM Enterprise Switch uses several feedback
methods. These methods operate internally between the ATM Interface
Module and the ATM Switch Fabric Module. They include Early Packet
Drop (EPD), Partial Packet Drop (PPD), Explicit Forward Congestion
Indication (EFCI), and Cell Loss Priority (CLP). These methods are
discussed in the sections that follow.