3Com 7600 manual ATM Network, Topics are discussed

13	TRAFFIC MANAGEMENT IN THE
	ATM NETWORK

	This chapter discusses the Traffic Management (TM) function within the
	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.

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