Cabletron Systems SmartCell 6A000 manual Traffic Management, Traffic Descriptors

Traffic Management Switch Administration

Note Do not change the VCC Mask for the CPU port (B4).

4.6TRAFFIC MANAGEMENT

This section describes how the SmartCell 6A000 ATM switch manages bandwidth and congestion. It briefly describes console commands that affect how the switch manages traffic. This section also provides guidelines for setting some traffic control parameters.

For information on troubleshooting congestion problems, see Chapter 5, "Troubleshooting."

The SmartCell 6A000 has extensive abilities for managing the flow of traffic. Traffic management includes all operations that insure optimum switch throughput, where throughput is based on rate of packet loss, available bandwidth, and traffic processing overhead. Under most conditions, the switch can efficiently and automatically manage 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.

The SmartCell 6A000 console commands affect traffic flow on a per-QoS, per-port, and global basis. These console commands affect switch traffic flow by controlling

•Bandwidth allocation

•Call Admission Control (CAC) policies

•Class of service 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.

4.6.1Traffic Descriptors

Traffic characteristics of an ATM source are signaled through a set of traffic descriptors during connection establishment. The SmartCell 6A000 uses traffic descriptors for resource allocation during call set up, and guarantees the QoS across the connection. The source traffic descriptor is a set of parameters that describes the expected bandwidth utilization of a connection. You can set these parameters, which include

•Peak cell rate (PCR)

•Sustainable cell rate (SCR) and maximum burst size (MBS)

•Minimum cell rate (MCR) and initial cell rate (ICR) — through UNI4.0 signaling only

Traffic descriptors vary for each QoS. 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.

4-18 SmartCell 6A000 User Guide