The document discusses various queuing methods used in routers to manage network traffic effectively, emphasizing the differences between softqueues and hard queues. It outlines various queuing strategies such as FIFO, priority queuing, and weighted fair queuing, detailing their configurations and guarantees for delay and bandwidth. Additionally, it highlights the features and scenarios for applying class-based weighted fair queuing and low-latency queuing, underscoring their significance in ensuring Quality of Service (QoS) for different types of network traffic.

1. Quality of Service(QoS)-Part 2
By : Reza Farahani

2. Queuing
The goal of queuing method?
routers can be configured to perform queuing for
packets that are waiting to exit an interface.
For example, if a router receives 5 Mbps of
traffic every second for the next several
seconds, and all that traffic needs to exit a T1
serial link, the router can’t forward all the
traffic.

3. Types of Queue
There are two types of Queue:
SoftQueue :
 The queues created on an interface by the queuing tools
are called software queues , as these queues are
implemented in software.
 However, when the queuing scheduler picks the next
packet to take from the software queues, the packet does
not move directly out the interface.

4. Types of Queue
Hard Queue :
Instead, the router moves the packet from the
interface software queue to a small hardware FIFO
queue on each interface.
Cisco calls this separate, final queue either
the transmit queue (Tx queue) or transmit
ring (Tx ring)

5. Queuing
Transmit Ring (TX Ring)
OR
Transmit Queue (TX Queue)

6. HW Queue
 Hardware queues provide the following features:

7. Length of HW Queue

8. Queuing
The size of the output queue affects delay,
jitter, and loss. Because the queue has a finite
size, it may fill
Length Of The Queue Tail Drop Delay Jitter
Queue
Scheduling

9. Router Queuing

10. Queuing Tools
FIFO
Priority queuing (PQ)
Custom queuing (CQ)
Weighted fair queuing (WFQ)
Class-based weighted fair queuing (CBWFQ)
Low-latency queuing (LLQ)

11. Queuing Methods-FIFO
Fist-In-First-Out
Number Of Queue = 1
Method = FIFO
Delay Guarantee = No
Bandwidth Guarantee = No
Recommended For Voice = No
Pointer to Memory

12. FIFO
R3(config)#int s 0/0
R3(config-if)#no fair-queue
R3#sh int s 0/0
.
.
Queuing strategy : fifo
Output queue :0/40 (size/max)
.
.
R3(config)#int s 0/0
R3(config-if)#hold-queue 50 out

13. Queuing Methods-PQ
Number Of Queue = 4 (High, Medium, Normal, and Low)
Method = Strict Priority
Delay Guarantee = Yes (Only for High Priority)
Bandwidth Guarantee = No
Recommended For Voice = Somewhat

14. PQ WORKFLOW

15. Queuing Methods-CQ
Number Of Queue = 16
Method = Round Robin
Delay Guarantee = No
Bandwidth Guarantee = Yes
Recommended For Voice = No

16. CQ WORKFLOW
Queue 1 5000 Byte 10%
Queue 2 5000 Byte 10%
Queue 3 10000 Byte 20%
Queue 4 10000 Byte 20%
Queue 5 20000 Byte 40%
Example:

17. Queuing Methods-WFQ
Number Of Queue = Per Flow(Max=4096)
Method = Weighted Fair
Delay Guarantee = No
Bandwidth Guarantee = No
Recommended For Voice = No
Small Packets service First!
Telnet
HTTP
FTP

18. WFQ Scheduler
32384
(IP_Precedence + 1)
SN= Previous_SN in Queue + (weight * new_packet_length)

19. WFQ Sequence Number Assignment Example

20. WFQ Sequence Number Assignment Example 2
Order of Packets : 13, 14, 15, 16, 9, 5, 10, 1, 11, 6, 12, 2, 7, 8, 3, 4

21. WFQ Modified Tail Drop
The hold-queue size limits the total number of packets in all of the flow or
conversation queues.
CDT limits the number of packets in each individual queue

22. Weighted Fair Queuing Points
WFQ does not allow classification options to be configured!
WFQ Classification
Flow-Based WFQ, or just WFQ, classifies traffic into flows. Flows are identified by at least five
items in an IP packet:
■ Source IP address
■ Destination IP address
■ Transport layer protocol (TCP or UDP) as defined by the IP Protocol header field
■ TCP or UDP source port
■ TCP or UDP destination port
■ IP Precedence
WFQ scheduler is to provide more bandwidth to flows with higher IP
precedence values and small length
In a network where most of the delay-sensitive traffic is lower-volume traffic,
WFQ is a great solution
WFQ can be configured for a maximum of 4096 queues, but interestingly, the actual value can
only be a power of 2 between 16 and 4096 because WFQ
performs a hash algorithm to classify traffic, and the hash algorithm only works when the
number of queues is one of these valid values

23. WFQ Configuration
R3(config)#int s 0/0
R3(config-if)#fair-queue
R3#show queueing fair
R3# show queue s 0/0
.
.
Queuing strategy: weighted fair
.
.
R3#configure terminal
R3(config)#int s 0/0
R3(config-if)#fair-queue 100 64 10
R3(config-if)#hold-queue 500 out

24. CB WFQ Queuing
Number Of Queue = 64
Method = N/A
Delay Guarantee = No
Bandwidth Guarantee = Yes
Recommended For Voice = No
CBWFQ=ECQ+ WFQ

25. CBWFQ

26. CBWFQ Functions and Features

27. CBWFQ

28. Class Based Weighted Fair Queuing Points
 CBWFQ supports two types of drop policy, namely tail drop and WRED.
 You can enable WRED on any of the 64 queues available with CBWFQ.
 CBWFQ supports 64 queues, with a maximum and default queue length
varying depending on the model of router and the amount of memory
installed.
 CBWFQ provides a great advantage by allowing WFQ to be used in the
class-default queue.
 If some queues do not need their bandwidth for a short period, the
bandwidth is spread across the other classes

29. CBWFQ Example Scenario
• R3 uses CBWFQ on its S0/0 interface
• All VoIP payload traffic is placed in a queue.
• All other traffic is placed in another queue.
• Give the VoIP traffic 50 percent of the bandwidth.
• WFQ and WRED should be used on the non-VoIP traffic.

30. CBWFQ Example Scenario
R3#show running-config
Building configuration...
ip cef
class-map match-all voip-rtp
match ip rtp 16384 16383
policy-map queue-voip
class voip-rtp
bandwidth percent 50
class class-default
fair-queue
interface Serial0/0
description connected to FRS port S0.
Single PVC to R1.
no ip address
encapsulation frame-relay
load-interval 30
bandwidth 128
service-policy output queue-voip
clockrate 128000

31. Low Latency Queuing (LLQ)
Number Of Queue = 1 PQ + CBFWQ
Method = N/A
Delay Guarantee = Yes (For PQ Traffic)
Bandwidth Guarantee = Yes
Recommended For Voice = Yes
LLQ= PQ+ CBWFQ

32. Low Latency Queuing (LLQ)

33. Cisco LLQ Bandwidth Allocation Recommendation

34. Comparisons of WFQ, CBWFQ, and LLQ