Cabletron Systems 9A100 - Manual (Page 59)

SmartSwitch 9A100 User Guide 4-17
Switch Administration Traffic Management
4.6 TRAFFIC MANAGEMENT
This section describes how the SmartSwitch 9A100 manages bandwidth and congestion. It briefly describes console
commands that affect how the SmartSwitch 9A100 manages traffic. This section also provides guidelines for setting
some traffic control parameters.
Note For information on troubleshooting traffic congestion problems, see Chapter 5,
“Troubleshooting.”
The SmartSwitch 9A100 has extensive abilities for managing the flow of traffic. Traffic management includes all
operations performed by the SmartSwitch 9A100 that ensure optimum switch throughput, where throughput is based
on rate of packet loss, available bandwidth, and traffic processing overhead. Under most conditions, the
SmartSwitch 9A100 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.
The SmartSwitch 9A100 provides 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.
4.6.1 Traffic Descriptors
Traffic characteristics of an ATM source are signaled through a set of traffic descriptors during connection
establishment. The SmartSwitch 9A100 uses traffic descriptors for resource allocation during call set up and
guarantees the Quality of Service (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,
• Peak Cell Rate (PCR)
• Sustainable Cell Rate (SCR) and Maximum Burst Size (MBS)
• Minimum Cell Rate (MCR) and Initial Cell Rate (ICR) — signaled 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.
SmartSwitch 9A100 user data cells are classified according to the state of a cell loss priority (CLP) bit in the header
of each cell. A CLP 1 cell has a lower priority than a CLP 0 cell and is discarded first. Source traffic descriptors can
specify CLP 0 cell traffic, CLP 1 cell traffic, or the aggregate CLP 0+1 traffic.