A presentation on Quality of Service of WLan using OPNET Modeler.

2. ACKNOWLEDGEMENT
 A BIG THANKS TO ALL WHO HAVE MADE THIS
PROJECT POSSIBLE ESPECIALLY TO THE HEAD OF
OUR DEPARTMENT FOR GIVING US THE
PERMISSION TO USE THE M.TECH LAB FOR OUR
PROJRCT WORK.
A VERY SPECIAL THANKS TO OUR PROJECT GUIDE
MRS. SANDHYA PATTANAYAK.WITHOUT HER
THIS PROJECT WOULD HAVE BEEN IMPOSSIBLE.

3. PROJECT DONE BY:-
SUSHANT KUMAR
VENKATESH PANDEY
SHABBIR CHUNAWALA
ALOK RANJAN UPADHYAY
PROJECT GUIDE:-
MRS.SANDHYA PATTANAYAK

4. CONTENTS
 AIM OF PROJECT
 OVERVIEW OF 802.11
 MAC PROTOCOLS
DCF PROTOCOL
EDCF PROTOCOL
 NETWORK SIMULATION & RESULTS
 CONCLUSION

5. AIM OF PROJECT
The main objectives of the Project are:
 The study of basic concepts and issues of Wireless/Cellular network that can
improve the QoS of a cellular WLAN. Mainly focusing on Medium Access
Control layer of Open Systems Interconnection (OSI) model.
 Study various existing Medium Access Control protocols of cellular WLAN.
 Implementation and comparison of efficient mechanisms that can improve
the
 QoS of WLAN by using OPNET Modeler’s wireless module.
 Study the results obtained, and recommend the best possible protocol that can
provide high QoS under respective network traffic conditions.

6. WHAT IS WLAN?
 A wireless LAN or WLAN is a wireless local area
network that uses radio waves as its carrier.
 The last link with the users is wireless, to give a
network connection to all users in a building or
campus.
 The backbone network usually uses cables.
Wireless LANs operate in almost the same way as
wired LANs, using the same networking protocols
and supporting the most of the same applications.

7. AN OVERVIEW OF IEEE 802.11
 IEEE 802.11 advantages：
• Broadband bandwidth capability
• Low deployment cost
• Internet services access anytime,
anywhere
• Mobility and connectivity
7

8.  IEEE 802.11 disadvantages：
 Best effort services
 No build in QoS modification of
existing standards required
 Shared medium
8

9. Interframe Spacing
 Varying interframe spacings create different
priority levels for different types of traffic.
 The high-priority traffic doesn't have to wait as
long after the medium has become idle.
 To assist with interoperability between different
data rates, the interframe space is a fixed amount
of time, independent of the transmission speed.
9

10.  Short interframe space (SIFS)
 The SIFS is used for the highest-priority
transmissions, such as RTS/CTS frames and positive
acknowledgments.
 PCF interframe space (PIFS)
 The PIFS is used by the PCF during contention-free
operation.
 Stations with data to transmit in the contention-free
period can transmit after the PIFS has elapsed and
preempt any contention-based traffic.
10

11.  DCF interframe space (DIFS)
 The DIFS is the minimum medium idle time for
contention-based services.
 Stations may have immediate access to the medium
if it has been free for a period longer than the DIFS.
 Extended interframe space (EIFS)
 It is not a fixed interval.
 It is used only when there is an error in frame
transmission.
11

12. MAC
PROTOCOLS

13. Distributed Coordination Function
(DCF)
 The DCF is the basis of the standard CSMA/CA
access mechanism.
 Like Ethernet, it first checks to see that the radio
link is clear before transmitting.
 To avoid collisions, stations use a random backoff
after each frame, with the first transmitter seizing
the channel.
13

14.  In some circumstances, the DCF may use the
CTS/RTS clearing technique to further reduce
the possibility of collisions.
 Most traffic uses the DCF, which provides a
standard Ethernet-like contention-based
service.
 The DCF allows multiple independent stations
to interact without central control, and thus
may be used in either IBSS networks or in
infrastructure networks.
14

15. Figure 6. RTS/CTS clearing
15

16. Backoff with the DCF
 A period called the contention window or backoff window
follows the DIFS.
 This window is divided into slots.
 Stations pick a random slot and wait for that slot before
attempting to access the medium; all slots are equally likely
selections.
 When several stations are attempting to transmit, the
station that picks the first slot (the station with the lowest
random number) wins.
16

17. Figure 7. Diagrammatic representation of DCF access
method
17

18. EDCF ( Enhanced DCF )
 EDCF is a contention-based channel access
scheme.
 EDCF provides differentiated service, distributed
access to the wireless medium for 8 delivery
priorities.
 EDCF access channel on each ESTA uses at most 8
prioritized output queues, one for each delivery
priority, called Traffic Categories (TCs).
18

19.  The CWmin and CWmax parameters can be set
differently for different traffic categories, such
as, a high priority TC with small values of
CWmin and CWmax.
 Instead of using a DIFS, as a minimum
specified idle duration time as defined in DCF,
a new kind of interframe space called
Arbitration Interframe Space (AIFS) is used.
19

20. Figure : Diagrammatic representation of EDCF
access method
20

21.  A single station may implement up to eight
transmission queues realized as virtual stations
inside a station, with QoS parameters that
determine their priorities.
 If the counters of two or more parallel TCs in a
single station reach zero at the same time, a
scheduler inside the station avoids the virtual
collision.
21

22. Figure : Virtual backoff of eight traffic categories
22

23. NETWORK
SIMULATIONS
& RESULT

25. APPLICATIONS CONFIGURED
 WEB BROWSING
(BACKGROUND)
 EMAIL(BACKGROUND)
 FILE TRANSFER (BEST
EFFORT)
 DATABASE ACCESS(BEST
EFFORT)
 VIDEO CONFERENCE
(INTERACTIVE MULTIMEDIA)
 VOICE(INTERACTIVE VOICE)

26. PROFILES CONFIGURED
 FTP,DATA,VOICE
 ALL APPLICATIONS
 WEB,EMAIL,FTP,
DATA
 WEB,EMAIL,
VIDEO
 WEB,EMAIL
 FTP,DATA
 VIDEO,VOICE

27. EDCA PARAMETERS
APPLICATION CWmin CWmax
VOICE 3 7
VIDEO 7 15
BEST EFFORT 31 1023
BACKGROUND 31 1023

28. RESULTS-DCF
THROUGHPUT MAC DELAY

29. RESULTS-EDCF

30. MAC DELAY
 THE MAC DELAY
VARIES WITH THE
PRIORITY LEVELS OF
THE APPLICATION.
HIGHER THE PRIORITY
LOWER THE MAC
DELAY.

31. COMPARISON OF DCF & EDCF
THE
THROUGHPUT OF
BOTH
PROTOCOLS
SEEMS TO BE
IDENTICAL.
THROUGHPUT

32. COMPARISON-MAC DELAY
THE MAC DELAY
OF EDCF IS
GREATER THAN
THAT OF DCF.
DCF PERFORMS
BETTER IN THIS
REGARD
MAC DELAY

33. COMPARISON-RETRANSMISSION
ATTEMPTS
THE NO. OF
RETRANSMISSION
ATTEMPTS FOR EDCF IS
MORE THAN DCF BECAUSE
OF A LARGE NO
COLLISSIONS.
DCF HAS COLLISSION
AVOIDANCE MECHANISM
THUS HAS LOW NO. OF
RETRANSMISSION.
RETRANSMISSION
ATTEMPTS

34. CONCLUSION
The results obtained from simulation shows that Enhanced
Distribution Coordination Function provides efficient
mechanism for service differentiation and hence provides quality
of service to the Wireless LAN. However, this improvement
comes at a cost of a decrease in quality of the lower priority
traffic up to the point of starvation. The acquisition of the radio
channel by the higher priority traffic is much more aggressive
than for the lower priority. Higher priority traffic benefited,
while lower priority traffic suffered. In terms of overall
performance (under the used simulation conditions in this
particular study of QoS of Wireless LAN), DCF performs
marginally well than EDCF. This happens due to reason that in
EDCF mechanism, each AC function acts like a virtual station for
medium access, so more collision will be expected for EDCF
scenario.

35. THANK YOU!!!!

36. QUESTIONS
??????