3com 7600 Benutzerhandbuch
13
T
RAFFIC
M
ANAGEMENT
IN
THE
ATM N
ETWORK
This chapter discusses the Traffic Management (TM) function within the
ATM network and its implementation in the 7600 Card. The following
topics are discussed:
ATM network and its implementation in the 7600 Card. The following
topics are discussed:
Q
Overview of the concepts and operation of Traffic Management
Q
How Traffic Management is implemented within the 7600 Card
Overview
ATM technology is intended to support a wide variety of services and
applications. Each type of application, whether it be voice, video or data,
has its own special data transmission performance requirements. These
requirements are expressed in a set of parameters called Quality of
Service (QoS) which includes such factors as permissible transmission
delay and loss of information. An important task of the ATM network is
to be able to provide the appropriate QoS requirements for each
application it is carrying. Traffic Management is provided on the ATM
network to protect the network and the end-system from congestion in
order to achieve network performance objectives. An additional role is to
promote the efficient use of network resources. TM allows the devices to
transmit over a broader bandwidth for longer periods of time, making the
network more efficient.
applications. Each type of application, whether it be voice, video or data,
has its own special data transmission performance requirements. These
requirements are expressed in a set of parameters called Quality of
Service (QoS) which includes such factors as permissible transmission
delay and loss of information. An important task of the ATM network is
to be able to provide the appropriate QoS requirements for each
application it is carrying. Traffic Management is provided on the ATM
network to protect the network and the end-system from congestion in
order to achieve network performance objectives. An additional role is to
promote the efficient use of network resources. TM allows the devices to
transmit over a broader bandwidth for longer periods of time, making the
network more efficient.
Service categories
The 7600 Card’s ATM data transmission Traffic Management is based on
the Available Bit Rate (ABR) or Unspecified Bit Rate (UBR) “service
categories”. ABR allows a flow control mechanism to be established
which supports data “feedback” to control the source data transmission
rate in response to changing ATM layer congestion. This feedback is
conveyed to the source through specific control cells called Resource
Management Cells, or RM-cells. An end-system that adapts its traffic in
accordance with the feedback will experience a low cell loss ratio and
obtain a fair share of the available bandwidth according to a network
specific allocation policy. No numeric commitment is made about cell
the Available Bit Rate (ABR) or Unspecified Bit Rate (UBR) “service
categories”. ABR allows a flow control mechanism to be established
which supports data “feedback” to control the source data transmission
rate in response to changing ATM layer congestion. This feedback is
conveyed to the source through specific control cells called Resource
Management Cells, or RM-cells. An end-system that adapts its traffic in
accordance with the feedback will experience a low cell loss ratio and
obtain a fair share of the available bandwidth according to a network
specific allocation policy. No numeric commitment is made about cell
abtthgde.book Page 1 Tuesday, June 23, 1998 10:29 AM