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Cisco AVVID Network Infrastructure Enterprise Quality of Service Design
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Chapter 4 QoS in an AVVID-Enabled Wide-Area Network
Verifying QoS
Note
The DSCP table reflects that the drop-preference bit is a factor in deciding which application to drop
first in the even of queue congestion. For example, DSCP 6 is (statistically) dropped more often than
DSCP 4, which is dropped more often than DSCP 2.
It may be surprising to see DSCP values other than 0, 2, 4 and 6 in the default queue, but this is perfectly
normal if the traffic is marked at CS6 or CS7 (IP Precedence 6 and 7). These IP Precedence values are
used by routing protocols.
Example 2
This second example is the output of a voice, video and data policy applied to a high-speed Frame Relay
PVC on a distributed platform (notice the hierarchical policy. In this example, you will note that:
·
There are no drops for voice traffic.
·
There are no drops for video traffic.
·
There are no drops for voice-control traffic.
·
Within the gold data, drops are increasing according to the drop-preference bit.
·
Within the silver data, drops are increasing according to the drop-preference bit.
·
Within the best-effort traffic, drops are increasing according to the drop-preference bit.
WAN-AGG-7500#show policy interface serial 1/0/1.50
Serial1/0/1.50: DLCI 150 -
Service-policy output: dTS-3072kbps
queue stats for all priority classes:
queue size 0, queue limit 337
packets output 252815, packet drops 0
tail/random drops 0, no buffer drops 0, other drops 0
Class-map: class-default (match-any)
780988 packets, 474070302 bytes
30 second offered rate 5758000 bps, drop rate 2997000 bps
Match: any
queue size 372,
queue limit 2560
packets output 463967, packet drops 314658
tail/random drops 314658, no buffer drops 0, other drops 0
Shape: cir 3072000, Bc 24576, Be 0
lower bound cir 0, adapt to fecn 0
output bytes 231123890, shape rate 2975000 bps
Queue-limit 1024
Service-policy : WAN-EDGE
Class-map:
VOICE (match-all)
204471 packets, 39258432 bytes
30 second offered rate 474000 bps,
drop rate 0 bps
Match: ip dscp 46
Priority: 17% (522 kbps), burst bytes 13050, b/w exceed drops: 0
Class-map:
VIDEO (match-all)
49118 packets, 32162946 bytes
30 second offered rate 388000 bps,
drop rate 0 bps
Match: ip dscp 34
Priority: 16% (491 kbps), burst bytes 30000, b/w exceed drops: 0