3Com 7600 manual ATM technology without having cell loss due to congestion, Configuration

Traffic Rates Shaping in the 7600 Card 13-5

QTraffic shaping is a mechanism that alters the traffic characteristics of a stream of cells on a VCC or a VPC to achieve a desired modification of those traffic characteristics. The VBR quality of service class makes use of traffic shaping.

QEFCI is a congestion notification mechanism that the ATM layer service user may make use of to improve the utility that can be derived from the ATM layer. The ABR quality of service class makes use of Explicit Forward Congestion Indication.

QExplicit Rate uses RM-cells to control the traffic rate through the network. The ABR quality of service class makes use of explicit rate.

Traffic Rates The 7600 Card implements Traffic Management that adheres to the Shaping in the 7600 emerging ATM Forum standards. The Traffic Management makes use of

Card	RM-cells for flow control to allow large networks to be created around
	ATM technology without having cell loss due to congestion.
	The 7600 Card Traffic Management hardware module contains an ASIC
	and local memory for traffic management tables. It performs processing
	on ATM cells emerging from or received by the ZipChip. This provides
	traffic rate shaping, additional statistics and flexibility in ATM network
	configuration.
	The 7600 Card checks connected devices for Traffic Management
	modules and only activates its own TM module if a corresponding one is
	found in the connected device.
	RM Cell Usage RM-cells are used by the network to control the rate flow. The RM cell
	format is as defined in the TM specification. These cells are sent at regular
	intervals from the 7600 Card and make their way through the network.
	In the event that there is congestion, the congestion bit of the RM cell is
	set by the destination end station. The RM cell is then returned to the
	source 7600 Card. In case the RM-cell is not returned to the source 7600
	Card or the CI bit is set, the traffic rate is automatically decreased. A
	received RM-cell with the CI bit cleared enables the sending 7600 Card to
	increase its sending rate.
	No RM-cells are sent on point-to-multipoint connection. Multicast rates
	are set in advance to avoid flooding the source with backward RM-cells.