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1. Quality
of
Service
By:
Abhishek Wadhwa, BVICAM

2. So what is it?
• Quality of service is the ability to provide
different priority to different applications,
users, or data flows, or to guarantee a
certain level of performance to a data flow

3. “ it defines the quality of service
as something a flow seeks to
attain”

4. Flow Characteristics

5. • Reliability : Lack of Reliability means
losing a packet or ack.
• Delay : Different applications can tolerate
delay in different degrees.
• Jitter : jitter is the variation in packets
belonging to same flow.
• Bandwidth : different application need
different b/w.

6. Techniques to improve
the quality of service.
Scheduling
FIFO QUEUING
PRIORITY QUEUING
WEIGHTED FAIR QUEUING
Traffic Shaping
LEAKY BUCKET
TOKEN BUCKET
Resource Réservation
Admission Control

7. Scheduling
• Packets from different flow arrive at switch
or router for processing
• A good scheduling technique treats the
different flow in a fair and appropriate
manner

8. • FIFO QUEUING

9. • Packets wait in a buffer (queue) until the
node is ready to process them.
• If avg. arrival rate>avg. processing rate
=>new packets will be discarded.
• FIFO QUEUING

10. Priority
Queuing

11. • Packets are assigned to a priority class
• Each class has its own queue.
• Higher class packets are processed first.
• Problem : Starvation
Priority
Queuing

12. Weighted Fair
Queuing

13. • Packets are still assigned to different
classes and admitted to different queues
• The queues are weighted based on the
priority
• Higher priority means higher weight
• If weight are 3,2,1 then 3 packets are
processed from q1,2 from q2,and 1 from
q1 in a round robin fashion
Weighted Fair
Queuing

14. Traffic Shaping
Is the mechanism to control the amount
and the rate of the traffic sent to the
network

15. Techniques to improve
the quality of service
Scheduling
FIFO QUEUING
PRIORITY QUEUING
WEIGHTED FAIR QUEUING
Traffic Shaping
LEAKY BUCKET
TOKEN BUCKET
Resource Réservation
Admission Control

16. Leaky Bucket
http://www.epubbud.com/read.php?g=5HEKFDZU&two=1&tocp=48

17. The rate at which water leaks from a bucket
does not depend on the rate at which the
water is input to the bucket
The input rate varies but the o/p remains
constant ,similarly ,network can
smooth out bursty traffic
Leaky Bucket

18. Token Bucket

19. Token Bucket
Leaky bucket does not taken into a/c idle host , if a
host is not sending for a while , its bucket becomes
empty.
If the host has bursty data ,leaky bucket allows
only avg. rate.
Token bucket takes into a/c the idle time , with
each clock tick the tokens are added to bucket
,when the data needs to be send ,it collects token
from bucket and then send the data packet
consisting of data=no of tokens

20. Techniques to improve
the quality of service
Scheduling
FIFO QUEUING
PRIORITY QUEUING
WEIGHTED FAIR QUEUING
Traffic Shaping
LEAKY BUCKET
TOKEN BUCKET
Resource Réservation
Admission Control

21. Resource Reservation
• A flow of data needs resources such as
buffer, bandwidth, CPU time, and so on .
• QoS can be improved if these resources
are reserved beforehand.

22. Techniques to improve
the quality of service
Scheduling
FIFO QUEUING
PRIORITY QUEUING
WEIGHTED FAIR QUEUING
Traffic Shaping
LEAKY BUCKET
TOKEN BUCKET
Resource Réservation
Admission Control

23. Admission Control
• Routers or switches puts restrictions on
the admission of packets from host.
• Before a router accepts the flow , it
checks the flow for specifications in
terms of bandwidth , buffer size ,cpu
speed etc.

24. Models deploying QoS
• Two models have been designed to
provide QoS:
->Integrated Service Model(IntServ)
->Differentiated Service Model(Diffserv)

25. IntServ
• User needs to create flow, kind of virtual
circuit ,from source to destination and
inform all routers of requirement

26. RSVP: Resource Reservation
Protocol
• Receiver based reservation : the receiver
not the sender make the reservation(eg :
youtube)
• RSVP messages:
->Path Messages
->Resv Messages

28. DiffServ
• The router routes the packet based in
the class of service defined in the packet
• It defines several classes such as
,constant bit rate class , the variable bit
rate class etc.

29. DiffServ*
• ToS: type of service field is used to
define the class of service for each
packet

30. DiffServ*
• ToS: type of service field is used to
define the class of service for each
packet

31. Conclusion:
 Flow characteristics
 Scheduling
 FIFO QUEUING
 PRIORITY QUEUING
 WEIGHTED FAIR QUEUING
 Traffic Shaping
 LEAKY BUCKET
 TOKEN BUCKET
 Resource Réservation
 Admission Control
 Models
 Integrated Model (Requirement in advance)
 Differentiated Model(Classes)

32. Any
Questions?

33. Thank You

34. References
• cisco.tu-sofia.bg/uploads/Additional/Cisco_QoS.pdf
• www.cs.columbia.edu/~coms6181/slides/13/quality-of-service.ppt
• www.cs.princeton.edu/courses/archive/spr03/cs461/lec12/lec12.ppt
• www.csb.uncw.edu/people/.../Topic%207%20Service%20Quality.p
pt
• http://www.rfc-
editor.org/search/rfc_search_detail.php?rfc=2474&title=quality+of+s
ervice&pubstatus%5B%5D=Any&pub_date_type=any
• http://www.epubbud.com/read.php?g=5HEKFDZU&two=1&tocp=48
• *for further reading ->page 9 of Cisco_QoS.pdf
• http://www.rfc-editor.org/