586 CHAPTER 22: QOS AND RSVPAfter you specify how the rate limit is expressed, you can specify a burstsize. The burst size is the maximum amount of data that you can transmitat the line rate before the transmission is policed. This valueaccommodates variations in speeds and allows you to occasionally exceedthe configured rate.Specifying ServiceLevelsWhen you define a control, you specify a service level (a transmit priority).Most of the service levels that you can specify represent a specifictransmit queue. You can assign service levels to conforming packets(packets that are within the rate limit) and to nonconforming excesspackets (packets that exceed the rate limit).For information on assigning an IEEE 802.1p priority to nonconformingexcess packets, see “QoS Excess Tagging” later in this chapter. Forinformation on the transmit queues and QoS bandwidth, see “TransmitQueues and QoS Bandwidth” later in this chapter.Service levels also define the loss-eligibility status for conforming andnonconforming excess. By default, conforming packets are notloss-eligible; nonconforming excess are loss-eligible.The Multilayer Switching Module supports these service levels:n High — For any type of rate limit, transmits the packet first (toppriority)n Best — For any type of rate limit, transmits the packet on a best-effortbasis (the default for conforming and nonconforming excess packets)n Low — For any type of rate limit, transmits the packet on alow-priority basisn Drop — For a rate limit of none, drops all conforming packets on allports associated with the classifiers. For a rate limit of receivePort oraggregate, drops all nonconforming excess packets.If you want to drop conforming packets for only a subset of ports, usethe receivePort or aggregate rate limit, set the rate limit to 0, andspecify the group of ports.If you specify drop for the service level for conforming packets (that is,you are using a rate limit of none), the Multilayer Switching Moduledoes not give you the option of specifying an IEEE 802.1p tag.
