Quality Of Service Part 1 Page 2
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2Q
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UALITY OF
ERVICE
ART
packetlife.net
Queuing Comparison
FIFO
PQ
CQ
WFQ
CBWFQ
LLQ
Default on Interfaces >2 Mbps
No
No
<=2 Mbps
No
No
Number of Queues 1
4
Configured
Dynamic
Configured
Configured
Configurable Classes
No
Yes
Yes
No
Yes
Yes
Bandwidth Allocation
Automatic
Automatic
Configured
Automatic
Configured
Configured
Provides for Minimal Delay
No
Yes
No
No
No
Yes
Modern Implementation
Yes
No
No
No
Yes
Yes
First In First Out (FIFO)
Priority Queuing (PQ)
LLQ Config Example
Class Definitions
High
! Match packets by DSCP value
Tx
class-map match-all Voice
Medium
Ring
match dscp ef
!
Normal
Hardware
class-map match-all Call-Signaling
Hardware Queue
Queue
match dscp cs3
Low
Packets are transmitted in the
!
order they are processed
class-map match-any Critical-Apps
Provides four static queues which
match dscp af21 af22
cannot be reconfigured
No prioritization is provided
!
Higher-priority queues are
Default queuing method on high-
! Match packets by access list
always emptied before lower-
class-map match-all Scavenger
speed (>2 Mbps) interfaces
priority queues
match access-group name Other
Configurable with the tx-ring-
Lower-priority queues are at risk
limit interface config command
Policy Creation
policy-map Foo
of bandwidth starvation
class Voice
Custom Queuing (CQ)
! Priority queue policed to 33%
Weighted Fair Queuing (WFQ)
priority percent 33
Queue A
500 B/cycle
class Call-Signaling
Flow 1
! Allocate 5% of bandwidth
Queue B
4500 B/cycle
bandwidth percent 5
Flow 2
Hardware
class Critical-Apps
Queue C
1500 B/cycle
...
Queue
Hardware
bandwidth percent 20
Flow n
Queue
! Extend queue size to 96 packets
Rotates through queues using
queue-limit 96
Weighted Round Robin (WRR)
Queues are dynamically created
class Scavenger
Processes a configurable number
per flow to ensure fair processing
! Police to 64 kbps
of bytes from each queue per turn
police cir 64000
Statistically drops packets from
conform-action transmit
Prevents queue starvation but
aggressive flows more often
exceed-action drop
does not provide for delay-
No support for delay-sensitive
class class-default
sensitive traffic
! Enable WFQ
traffic
fair-queue
Class-Based WFQ (CBWFQ)
Low Latency Queuing (LLQ)
! Enable WRED
random-detect
Queue A
512 Kbps Min
Priority
512 Kbps Max
Policy Application
interface Serial0
Queue B
1024 Kbps Min
! Apply the policy in or out
Queue A
512 Kbps Min
Hardware
service-policy output Foo
Default
Remainder
Queue
Queue B
1024 Kbps Min
LLQ Config Example
Hardware
WFQ with administratively
Default
Remainder
Queue
configured queues
show policy-map [interface]
Each queue is allocated an
CBWFQ with the addition of a
Show interface
amount/percentage of bandwidth
policed strict-priority queue
show queue <interface>
No support for delay-sensitive
Highly configurable while still
traffic
supporting delay-sensitive traffic
Show mls qos
by Jeremy Stretch
v2.0
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