Users Guide

You can optionally include overhead fields in rate metering calculations by enabling QoS rate adjustment.
QoS rate adjustment is disabled by default, and no qos-rate-adjust is listed in the running-
configuration
• Include a specified number of bytes of packet overhead to include in rate limiting, policing, and
shaping calculations.
CONFIGURATION mode
qos-rate-adjust overhead-bytes
For example, to include the Preamble and SFD, enter qos-rate-adjust 8. For variable length
overhead fields, know the number of bytes you want to include.
The default is disabled.
The range is from 1 to 31.
Enabling Strict-Priority Queueing
In strict-priority queuing, the system de-queues all packets from the assigned queue before servicing any
other queues. You can assign strict-priority to one unicast queue, using the
strict-priority
command.
• Policy-based per-queue rate shaping is not supported on the queue configured for strict-priority
queuing. To use queue-based rate-shaping as well as strict-priority queuing at the same time on a
queue, use the Scheduler Strict feature as described in Scheduler Strict.
• The strict-priority supersedes bandwidth-percentage and bandwidth-weight
percentage configurations.
• A queue with strict priority can starve other queues in the same port-pipe.
NOTE: Assigning strict priority scheduling to a unicast queue on all ports using a global
command is not supported. However, you can configure both unicast and multicast queue
belonging to a dot1p to use strict priority scheduling using policy maps and then associate the
policy map to the egress interface.
Weighted Random Early Detection
Weighted random early detection (WRED) is a congestion avoidance mechanism that drops packets to
prevent buffering resources from being consumed.
NOTE: On the switch, WRED and Explicit Congestion Notification (ECN) marking are supported on
front-end I/O and backplane HiGig ports. When you enable WRED, packets are dropped during
times of network congestion based on the configured minimum and maximum WRED thresholds.
ECN marks packets for later transmission (instead of dropping them) when the network recovers
from a heavy traffic condition. For information about how to configure weights for WRED and ECN
operation, see Configuring Weights and ECN for WRED.
Traffic is a mixture of various kinds of packets. The rate at which some types of packets arrive might be
greater than others. In this case, the space on the buffer and traffic manager (BTM) (ingress or egress) can
be consumed by only one or a few types of traffic, leaving no space for other types. You can apply a
WRED profile to a policy-map so that specified traffic can be prevented from consuming too much of the
BTM resources.
Quality of Service (QoS)
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