Cisco Systems 8600 Series manual Traffic Management Overview, Traffic Parameters, QoS Parameters

Traffic Management Overview

Traffic Management Overview

The ATM Forum Traffic Management 4.0 Specification defines five basic traffic classes:

•CBR (Constant Bit Rate)

•rt-VBR (Real-Time Variable Bit Rate)

•nrt-VBR (Non-Real Time Variable Bit Rate)

•UBR (Unspecified Bit Rate)

•ABR (Available Bit Rate)

Table 7-1summarizes the major attributes of each of the traffic management classes:

Table 7-1	Standard ATM Traffic Classes
Attribute		CBR	rt-VBR	nrt-VBR	UBR	ABR
Traffic Parameters
PCR & CDVT		x	x	x	x	x
SCR & MBS			x	x
MCR						x
QoS Parameters
Pk-to-Pk CDV		x	x
Max CTD		x	x
CLR		x	x	x		nw specific
Other Attributes
Congestion Control						x
Feedback

Traffic parameters are defined as:

•PCR (Peak Cell Rate in cells/sec): the maximum rate at which a connection can transmit

•CDVT (Cell Delay Variation Tolerance in usec): establishes the time scale over which the PCR is policed. This is set to allow for jitter (CDV) that is introduced for example, by upstream nodes.

•MBS (Maximum Burst Size in cells): is the maximum number of cells that may burst at the PCR but still be compliant. This is used to determine the BT (Burst Tolerance) which controls the time scale over which the SCR (Sustained Cell Rate) is policed.

•MCR (Minimum Cell Rate in cells per second): is the minimum cell rated contracted for delivery by the network.

QoS (Quality of Service) parameters are defined as:

•CDV (Cell Delay Variation): a measure of the cell jitter introduced by network elements

•Max CTD (Cell Transfer Delay): is the maximum delay incurred by a cell (including propagation and buffering delays.

•CLR (Cell Loss Ratio): is the percentage of transmitted cells that are lost.

Congestion Control Feedback:

•With ABR, provides a means to control flow based on congestion measurement.

ATM Connections 7-3