implementation and performance analysis of modified mac for wlan

8/9/2019 Implementation and performance analysis of modified mac for wlan

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Implementation and Performance

Analysis of Modified MAC for WLAN

Project GuideMr. Ashok Kumar

Presented by:

Munish Bansal(06429)

Rohit Raina(06433)

Aneesh Mahajan(06435)


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ContentsContents

y Introduction

y Motivation

y IEEE 802.11 Standard

y IEEE 802.11 Architecturey OSI Model

y MAC layer

y DCF

y Simulation and Analysis

y Results

y Conclusion


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IntroductionIntroduction

y Wireless networks are becoming very popular

today

y Simplifies networking by enabling multiple users

to access a shared medium without additionalwiring

y Provide flexibility of location and data ports

y Cost effective alternative to physical LAN

y Similar to Ethernet ,802.11 focuses on two lower

layers of OSI model


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MotivationMotivation

y Real time applications have stringent requirements of

QoS in terms of delay, throughput etc

y

IEEE 802.11 does not offer any inherent support for real

time applications.

y IEEE 802.11e standard has been proposed but majority

of current WLAN infrastructure is 802.11 based.

y Need of IEEE 802.11 based QoS mechanism.


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IEEE 802.11 StandardIEEE 802.11 Standardy 802.11 specification as a standard was ratified by

IEEE in the year 1997

y 802.11offers data rates 1-2 Mbps

y 802.11a offers data rates upto 54 Mbps

y 802.11b offers data rates 5.5 and 11 Mbps

y In the original standard, there were two different typesof spread spectrum transmissions defined for thePhysical Layer

1.Direct Sequence Spread Spectrum (DSSS)2.Frequency Hopping Spread Spectrum (FHSS)

y The 802.11b standard works further with the DirectSequence Spread Spectrum


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IEEE 802.11 Architecture 1IEEE 802.11 Architecture 1


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y IBSS:It is peer to peer mode where the stationscommunicate directly without intermediate access

point.

y Also called Ad-hoc mode


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y BSS: Here all the stations communicate with each other

through an Access Point

y ESS: consists of two or more BSS connected by

Distribution system.


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MAC layerMAC layer

MAC layer covers three functional areas

Reliable Data delivery: Achieved through frame

exchange protocol at the MAC level.

Access Control: Achieved in two ways a distributed

access mechanism DCF and centralized access

mechanism called PCF

Security: Achieved by incorporation ofWEP


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Distributed CoordinatedDistributed Coordinated

Function(D

CF)Function(D

CF)


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DCF Access MethodDCF Access Method


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Modified DCFModified DCFy Normal Contention Window

y Non Overlapping Modified DCF

y

Overlapping Modified DCF


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The Simulation Tool: OPNETThe Simulation Tool: OPNET


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Available Statistics for WLANAvailable Statistics for WLAN

y Delay: End-to-end delay of all packets received by the nodes

wireless LAN MAC and forwarded to the higher layer.

y Load: Total number of bits received from the higher layer. Packets

arriving from the higher layer are stored in the higher layer queue.

y Throughput: Total number of bits sent to the higher layer from the

MAC layer. The data packets received at the physical layer are sent

to the higher layer if they are destined for this station.

y Data dropped: It represents buffer overflow i.e the receiving

station receives more data than it can process


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AnalysisAnalysis

Without Modified DCF

11 Mbps,DSSS


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2 Mbps,DSSS


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11 Mbps ,Multiple Nodes, DSSS


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11 Mbps ,FHSS


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Low Load Analysis, ModifiedLow Load Analysis, Modified

DCF

DCFDelay

X-axis :Delay (sec) ,Y-axis : Time(sec)


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y Throughput

X-axis :Throughput(bits/sec) ,Y-axis : Time(sec)


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Data drop

X-axis :Data drop(bits/sec) ,Y-axis :Time sec


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Medium Load Analysis, ModifiedMedium Load Analysis, Modified

DCFDCFDelay

X-axis :Delay(sec) ,Y-axis :Time(sec)


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Throughput



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Data Drop


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High LoadHigh Load Analysis.ModifiedAnalysis.Modified

DCFDCFDelay

X-axis :Delay(sec) ,Y-axis : Time(sec)


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Throughput



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Data Drop

X-axis :Data drop(bits/sec) ,Y-

axis : Time(sec)


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ResultsResults

DELAY (IN SECONDS) AS COMPARED TONORMAL 802.11


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THROUGHPUT (IN BITS/SECOND) AS

COMPARED TO NORMAL 802.11


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DATA DROP (IN BITS/SECOND) AS

COMPARED TO NORMAL 802.11


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ConclusionConclusion

First four scenarios

y DSSS is best method for transmitting the data in

WLAN.

y Throughput decreases as we add more node tothe network.

y As we decreased the data transmission speed

from 11mbps to 2mbps the throughput also

decreased.


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Modified DCF(Overlapping and non

overlapping)

y From the results we can observe that

overlapping and non-overlapping case is

suitable for the medium and high load cases,though delay is increased to some extent in

modified case.

y Thus it seems appropriate to use modified DCF

for real time applications such as videoconferencing


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ReferencesReferences[1] Jim Zyren and Al Petrick, Brief Tutorial on IEEE 802.11 Wireless LANs, February

1999.

[2] Wanang Xiao, Yin Shi, A Two-Step Backoff Scheme for Improving the Performanceof the IEEE 802.11 distributed Coordination Function, ISCIT2005

[3] William Stallings, Data and computer communication, 5th edition, 2005

[4] Min Sheng and Yanhui Chen, Performance evaluation of modified IEEE 802.11mac for multi channel multi-hop network , April, 2003.

[5] Charles E. Perkins, Performance Comparison of On-Demand Routing Protocols forAd Hoc Networks, IEEEPersonal Communications, Feb. 2001.

[6] G. Bianchi, Performance analysis of the IEEE 802.11 distributed coordinationfunction, IEEE Journal of Selected Areas in Telecommunications, Wireless series,vol. 18, pp. 535547, Mar. 2000.

[7] Pablo Brenner , A Technical tutorial on the IEEE 802.11 Protocol , July 2005


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[8] S.Rackley, Wireless Networking Technology from Principles to SuccessfulImplementation, Jordan Hill, 2007

[9] Dr. Mohammad Hussian Ali & Manal Kadhim Odah, Simulation Study 0f 802.11bDCF Using OPNET Simulator , Eng. & Tech. Journal, Vol. 27, No 6 ,2009

[10] P. Gupta, R. Gray and P. R. Kumar, An Experimental Scaling Law for Ad HocNetworks, www.black.cs1.uiuc.edu/~prkumar

[11] Jeevan Chalke, Avadhoot Punde, Kedar Rudre, Modified DCF MAC in OPNET,A report on Mobile computing, November 2006.

[12] J. Theunis, B. Van den Broeck, P. Leys, J. Potemans1, E. Van Lil, A. Van de Capelle, OPNET in Advanced Networking Education, Katholieke Universiteit LeuvenMarch 2008.

[13] Xinjie Chang, Network simulation with OPNET, Network Technology ResearchCenter School of EEE Nanyang Technological University SINGAPORE,Proceedings of the 1999 Winter Simulation Conference.


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ThankThank YouYou

implementation and performance analysis of modified mac for wlan

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