Nortel business policy switch 2000 User Manual page 303

Chapter 4 Policy-enabled networks 303
Once you configure one Policy with a Shaping Group, you can configure
additional Policies that reference existing Shaping Group numbers—this is
aggregate shaping. All Policies with the same Shaping Group number are shaped
at egress as if they were a single Policy.
To define shaping criteria, you set a Shaping Rate in Kbps (1000 bits per second in
each Kb/s) and a Shaping Burst Rate that specifies an allowed data burst larger
than the Shaping Rate for a brief period. After you specify the Shaping Burst Rate,
you choose among up to 6 possible Shaping Burst Rate Durations. Finally, you set
the shaping queue size, which is used to configure the size of the shaping queue.
Note: You must enter a multiple of 64 Kbps as the shaping rate.
An example of rate shaping is limiting traffic egressing a port to a specified
transmission rate, such as 64 Kbps (Shaping Rate). Instead of dropping all traffic
that exceeds this threshold, you can configure a Shaping Burst Size that allows the
switch to exceed the designated Shaping Rate for a brief period without delaying
the traffic. Traffic that exceeds the threshold (Shaping Rate) for longer periods is
delayed. This combination of actions "shapes" the traffic to conform to the
designated maximum transmission rate. The switch temporarily buffers the
delayed traffic. You choose the number of packets you want buffered when you
configure the Queue Size. If traffic is received at a rate greater than it can be
transmitted, based on the configured maximum transmission rate, for an extended
period, the switch's buffering resources are exhausted and that traffic is dropped.
You can shape only those traffic flows that have an IEEE 802.1p value that is
known at egress. Table 60 shows the type of traffic that can be shaped on trusted,
untrusted, and unrestricted interface classes.
Using the Business Policy Switch 2000 Version 2.0