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• Include a specied 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 elds, 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 congured 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 congurations.
• 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 congure 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 buering resources from
being consumed.
NOTE
: On the switch, WRED and Explicit Congestion Notication (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 congured minimum
and maximum WRED thresholds. ECN marks packets for later transmission (instead of dropping them) when the network
recovers from a heavy trac condition. For information about how to congure weights for WRED and ECN operation, see
Conguring Weights and ECN for WRED.
Trac 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 buer and trac manager (BTM) (ingress or egress) can be consumed by only one or a few types of trac, leaving no
space for other types. You can apply a WRED prole to a policy-map so that specied trac can be prevented from consuming too much
of the BTM resources.
WRED uses a prole to specify minimum and maximum threshold values. The minimum threshold is the allotted buer space for specied
trac, for example, 1000KB on egress. If the 1000KB is consumed, packets are dropped randomly at an exponential rate until the maximum
threshold is reached (as shown in the following illustration); this procedure is the “early detection” part of WRED. If the maximum threshold,
for example, 2000KB, is reached, all incoming packets are dropped until the buer space consumes less than 2000KB of the specied
trac.
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Quality of Service (QoS)