3Com 7600 manual Traffic, Functions

13-4CHAPTER 13: TRAFFIC MANAGEMENT IN THE ATM NETWORK

	the sending rate is reduced. When the source end station receives a
	backward RM cell with the CI bit cleared it may increase the sending
	rate on that particular VC.
Explicit Rate Control	Explicit rate control enhances the implicit rate control by adding the
	explicit rate (ER) field to the RM cell. In this field the source end station
	indicates the rate at which it would like to transmit. If an explicit rate
	switch exists in the virtual connection (VC) route it may reduce the ER
	field in the backward RM-cells in case of congestion. In this case it
	indicates explicit rate for the source end station. The source end station,
	upon receiving the backward RM-cells, adjusts its sending rate according
	to the ER field.
	The traffic management standard as defined by the ATM forum supports
	VC routes with both explicit and implicit switches. The standard specifies
	how to handle lost RM-cells as well as fairness between competing ABR
	connections and enhancements for better link utilization.
Traffic and	The following describes the available traffic and congestion control
Congestion Control	functions:
Functions	Q Network resource management may be carried out by using virtual
	paths. Virtual path connections may be used to separate traffic,
	thereby preventing statistical multiplexing with other types of traffic.
	The CBR and VBR quality of service classes make use of network
	resource management.
	Q Connection admission control is defined as the set of actions taken by
	the network in order to establish whether a virtual channel or virtual
	path connection can be accepted. The CBR and VBR quality of service
	classes make use of connection admission control.
	Q Usage parameter control is defined as the set of actions taken by the
	network to monitor and control traffic in terms of traffic ordered and
	validity of the ATM connection at the user access. The CBR and VBR
	quality of service classes make use of usage parameter control.
	Q Selective cell discarding by network elements of the CLP=1 flow while
	still meeting network performance objectives on both the CLP=0 and
	CLP=1 flows. The VBR quality of service class makes use of selective
	cell discarding.