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SmartSwitch ATM User Guide 6-1
6 TRAFFIC MANAGEMENT
6.1 TRAFFIC MANAGEMENT CAPABILITIES
ATM SmartSwitches have extensive abilities for managing traffic flow. Traffic management includes all operations
performed by the ATM SmartSwitch that ensures optimum switch throughput, where throughput is based on rate of
packet loss, available bandwidth, and traffic processing overhead. Under most conditions, an ATM SmartSwitch can
efficiently and automatically manage switch traffic. However, if necessary, you can adjust the switch traffic
management parameters. For example, it might be necessary to adjust parameters for a port that carries a large amount
of CBR traffic or a very large number of simultaneous connections.
ATM SmartSwitches provide console commands that affect traffic flow on a global, port, or category of service level.
These console commands affect switch traffic flow by controlling
• Bandwidth allocation
• Call Admission Control (CAC) policies
• The service category for a connection
• Buffer memory allocation
• Threshold settings for anti-congestion routines
Caution Do not change traffic control settings unless you have expert-level experience
with ATM switching. Back up the switch configuration before making changes.
Also, make notes of the changes you make to the traffic control parameters.
6.1.1 Traffic Descriptors
Traffic characteristics of an ATM source are signaled through a set of traffic descriptors during connection
establishment. ATM SmartSwitches use traffic descriptors for resource allocation during call set up to guarantee the
quality of service (QoS) across the connection. The source traffic descriptor is a set of parameters that describes the
expected class of service and bandwidth utilization of a connection. Depending on the class of service specified in the
traffic descriptor you can set the following parameters:
• Peak Cell Rate (PCR)
• Sustainable Cell Rate (SCR)
• Maximum Burst Size (MBS)
• Minimum Cell Rate (MCR) — signaled through UNI4.0 signaling only
• AAL type
If a connection is bi-directional, a traffic descriptor has to be assigned to each direction and need not be the same in
both directions.