Dcf Distributed Coordination Function Computer Science Essay

Dcf Distrisolelyed Coordination Function electronic computer skill Essayatomization It is the turn characterd in macintosh IEEE 8021.11 to breaking away a packet into little pieces. atomisation is transit that dividing long systema skeletale to several(prenominal) shorter frame. Using this technology beca employ the radio LANs slang high telephone number defect lay outs. The probability of losing frame is oft metres higher(prenominal) for tuner links. The 802.11 uses atomisation to wince the frame misunderstanding rove.The PCF is supporting sensitivity occupation and support approximately high priority application. consequently the real time application discipline imply to transmitted with extinct any delay. The probability of lost frame is much higher for wireless links. Thats wherefore atomisation is used to Reduces amount of time mediocre is in use and Reduces probability of collisions. And at that place some permeable engage has been d sensa tion which related to our title, go away be shown in side by side(p) segmentations.Ac have it offledgmentAcknowledgments the patience and support of my family was the biggest care in the completion of this project. And would withal wish to acknowledge for my all overseervisor Mr.Manssor Ali and for module tutor Prof. Vallavarj, and module leader Mr. Vijay Krishna, for their guiding. too, I would like to thank the project coordinator Ms. Pravenna , for encouraging me to complete this cut venture and my carry.NomenclatureMAC Medium Access Control.DCF Distributed Coordination Function.PCF school principal Coordination Function.AP Access Point.BSS basal Service Set.IBSS Independent prefatorial Service Set.ESS Extend Service Set.RTS pass on To Send.CTS Clear To Send.ACK acknowledgment.OSI Open System Interconnection.LLC consistent Link Control.HTTP Hyper Text remove ProtocolNAV net profit Allocation Vector.DSSS Direct Sequence Spread Spectrum. circumscribe rapscallion Contents.. Page NoAbstract.. iAcknowledgementiiNomenclature..iiiContents page..ivList of pulpsvChapter 1 penetration71.1) General Information..71.2) Aim Of the project71.3) Project Objective..81.4) Honors challenges.8Chapter 2 literature check out..9Background..9IEEE MAC 802.11physical work10what is atomization.10 wherefore we argon victimisation this Technology.12The advantages and disadvantages of fragmentation..12Distributed Coordination function (DCF)13Fragmentation Operation.14Point Coordination function (PCF)..15Analysis The earliest work in selective information fragmentation IEEE802.1116Chapter 3 Literature Review psycho compend..19solutions for all above jobs.19 future(a) Work..20Chapter 4 Research Problem.21Chapter 5 Design and Experiment Setup..22Chapter 6 expiry.23Chapter 7 References.25List of figures view name Page No. presage (1) Independent Basic Service Set(IBSS) 11Figure (2) basis Basic Service Set 11Figure (3) Fragmentation The RTS/CTS access system. 1 3Figure( 4) MSDU startd into several MPDU 14Figure (5). Combination DCF PCF. 15Figure (6) The gist of (polling overhead )on profits throughput17Figure (7),Effect of fragmentation. 18Figure (8), wireless fidelity Setup diagram in OPNET.. 22Chapter 1 Introduction1.1) Aim employment on the effect selective information fragmentation on the performance of IEEE 802.11 wireless LAN chthonian PCF expressive style.fragmentation used to increase reliability transmit frame by divide 802.11 frames into smaller pieces (fragments) that are move separately to the destination.1.2) The objectives in this piece of music go forth be as follows1)The starting signal objective in this paper go pop out be understand the opening and different samples of IEEE 802.11.2)To understand the what are structure of the wireless profits3)To treasure and analyse the effect info fragmentation on the performance of IEEE 802.11 wireless LAN under PCF mode.)Selection for suitable simulation tool45)To design suitable WALN with usurp settings6)Study the critical valuation of the response.1.3) Honours challengeCritical analysis and evaluation of the results.Experimental Investigation of existing work.1.4) General InformationThe motivation i select this project title , is because in my organization they are feel for wireless entanglement technology ,which kindle provide much(prenominal) applications like for delivering traffic for real-time applications such as interpretive program and data . in that respectfore IEEE 802.11 under taper coordinate function PCF infract the axe satisfy the urgency, we get out see that later.wireless local area network (wireless local area network), win pile on the move to conduct with anyone and anywhere at anytime Caledonian college is one lift out character which is providing wireless religious service inside the college camps which allows the student to share data and network brows.The IEEE 802.11 WLAN has two different type of method origin accessing ,the distributed coordination function (DCF) and point coordination function (PCF). DCF is based on the carrier thought multiple access with collision avoidance (CSMA/CA) mechanism, while PCF is based on using the polling technique. The DCF mode of operation consists of two techniques for packet transmitting. In the nonpayment its operate as a two-way handshaking technique where a positive acknowledgment is transmitted by the receiver mail. (Stallings, 2007) .Fragmentation It is the run of breaking apart a packet into smaller pieces. A ejaculate (wireless earnings Interface Card or access point) uses for fragmentation is to divide 802.11 frames into smaller pieces (fragments) that are sent separately to the destination. The fragments are all label in a way that allows the destination device to put them cover charge together again after it gets all the fragments.1.5)The some of earliest work in data fragmentation IEEE802.11 kinetic Fragmentation Schem e fro point -Adaptive WLAN.7Improving the substance Throughput of Access Points in IEEE802.11 radio set LANs26.Performance Analysis of Packetized instance Transmission with PCF in IEEE802.11Wirelessnetwork.27Delay Analysis of IEEE 802.11 PCF MAC based Wireless vetworks.28Performance Evaluation of the IEEE 802.11 Wireless LAN Standards 6.Performance Enhancement of Wireless Local Networks. 20Chapter 2 Literature ReviewBefore we result go in depth of our title on data fragmentation under PCF mode , we must understand The fundamental building block of the WLAN network in IEEE 802.11., And our first objective lead be cover in this section.2.1) BackgroundIn this section we will be discussing about wireless local area network (WLAN), which make people on the move to communicate with anyone and anywhere at anytime Caledonian college is one best example which is providing wireless service inside the college camps which allows the student to share data and web brows ,but increase demand on portable figurer for example Laptops and increase communication equipment, its has responsibility of increasing in wireless network service. As we know this technology is operative under protocols to control the service amid users. Each type of wireless data network operates on a specific set of radio frequencies. For example, most Wi-Fi networks operate in a special band of radio frequencies round 2.4 gigahertz that realise been mute in most parts of the world for unlicensed point-to-point spread spectrum radio services. Other Wi-Fi systems use a different unlicensed band around 5 GHz. (Ross , 2008)) IEEE MAC 802.11physical layer are defined in one-third type2.2Direct sequence spread spectrum (DSSS)its operating in the 2.4 GHz band at data rate of 1Mbps and 2Mbps, the account of send packingalizes in stock(predicate) depend on the bandwidth.Frequency hopping spread spectrum(FHSS) operating in 2.4GHz at data rates of 1Mbps and 2Mbps, the available contain range is 23 in japan,70in USA.Infrared data rate is 1Mbps and 2Mbps operating at a wavelength between 850and 950 nm.For IEEE 802.11 at that place are different standards as we gouge see ,but my field will be based on IEEE 802.114 IEEE 802.11 Carrier Sense triune Access with Collision Avoidance (CSMA/CA) Medium Access Control (MAC), and 1 and 2 Mbps for DSSS, FHSS in 2.4 GHz band, and Infrared, ratified in 1997. IEEE 802.11a Works at 6, 9, 12, 18, 24, 36, 48 and 54 Mbps in 5GHz band, ratified in 1999. IEEE 802.11b Works at 5.5 and 11 Mbps in 2.4 GHz band, ratified in 1999.IEEE 802.11e MAC enhancements for fictional character of Service (QoS), work ongoing.( Stallings,2005)2.3) There are four physical components standards for 802.11 network Access point-Station--Wireless Medium-Distribution SystemThe basic structure block ,of the WLAN network is the 802.11 basic service set (BSS). A BSS defines a reportage area where all commits within the BSS connected.There are deuce BSS network topolog iesIndependent BSS (IBSS) NetworksInfrastructure BSS NetworksThe first one, In the independent BSS network positions, as it shown in figure(1) are communication directly with each other. Also its called the IBSS as ad-hoc network, used to communicate all station in groundwork network together . An ad -hoc network operates from one station to some other station nimblely, without any help from other device, thats mean no extremity for permission to access. This operation is working by using the independent basic service set(IBSS) .Figure (1) Independent Basic Service Set(IBSS)Second an Infrastructure Basic Service Set(BSS) as we can see in figure, (2) is a type of IEEE 802.11 network consists from station and access point(AP), which are used to communicate all station by (BSS).This will work when first station is sending the information to AP and than the AP forward this information to station which let the information pass to a wired node and the AP passes to fixed network. This available at (http//msdn.microsoft.com/en-us/library/ff556962(VS.85).aspx)Figure (2)Infrastructure Basic Service Set (http//msdn.microsoft.com/en-us/library/ff556962(VS.85).aspx)1 what is Fragmentation? and 2 Why we are using this Technology?2.4) what is Fragmentation?In this section we understand the Fragmentation It is the process of breaking apart a packet into smaller pieces. Fragmentation is process that dividing large frame into several shorter frame. Each fragment consists of a MAC Layer heading and frame check sequence (FCS), and a fragment flesh representing its request to position within the frame. Because the source station transmits each fragment independently, the receiving station reply with separate acknowledgement for each fragment (Yuguang and Kwon,2003 ) . All fragments are generate with equal size at same time, and all fragments will not change until they are transmitted in both PCF and DCF.2.5) Why we are using this Technology?Using this technology because th e Wireless LANs have high bit error rates.The probability of lasing frame is much higher for wireless links.802.11 uses fragmentation to reduce the frame error rate.2.6)The advantages and disadvantages of fragmentationAdvantages To reliability of data exchange between the stations. The uses fragmentation to reduce the frame error rate and fragmentation for bigger sized packets improves .Disadvantage fragmentation will increase the overhead. (Tamer Khatteb,2009)2.7) Distributed Coordination function (DCF)In 802.11, DCF also provides an optional way of transmittance data frames that involve contagion of special short RTS and CTS frames to the contagious disease of unquestionable data frame. As shown in Fig(.3) an RTS frame is transmitted by a station, which needs to transmit a packet. When the destination receives the RTS frame, it will transmit a CTS frame after SIFS interval immediately following the reply of the RTS frame.Figure(3) Fragmentation The RTS/CTS access method (Anon .,2003)The source station is allowed to transmit its packet scarce if it receives the CTS correctly. Note that all the other stations are capable of update the NAVs based on the RTS from the source station and the CTS from the destination station, which helps to combat the abstruse terminal problems In fact, a station able to receive the CTS frames correctly, can avoid collisions stock-s trough when it is unable to sense the data transmission systems from the source station. If a collision occurs with two or more RTS frames, much less bandwidth is haggard when compared with the situations where larger data frames in collision.(Haitao ,et al.,2002)2.8) The Fragmentation operationA 802.11 data link layer is divided in two sub layers Logical Link Control (LLC) and Media Access Control(MAC). In 802.11, a MAC service data unit (MSDU) could be divided into a sequence of smaller MAC protocol data unit (MPDUs) as it (shown in figure 4). Fragmentation creates MPDUs smaller than the orig inal MSDU length to increase the reliability, by increasing the probability of successful transmission of the MSDU in cases where channel characteristics limit reception reliability for longer frames. Fragmentation is able at each immediate transmitter. The process of combine MPDUs into a single MSDU is called as defragmentation . Defragmentation is adept at each immediate destination Only MPDUs with a unicast receiver hide will be garbled. Broadcast multicast frames shall not be fragmented level off if their length exceeds a Fragmentation Threshold When a directed MSDU is current from the LLC with a length greater than a Fragmentation Thresholdthe MSDU shall be fragmented. The MSDU is divided into MPDUs. Eachfragment is a frame no larger than a Fragmentation Threshold. (Yuguang and Kwon,2003 ).Figure( 4) MSDU divided into several MPDU. (Yuguang and Kwon,2003 ).) Point Coordination function (PCF)2.9PCF is working in combination with DCF as it shown in figure (5). PCF works suita ble for high traffic load, In PCF, the AP acts in the role of the point coordinator, and it controls the medium access, If point coordinator hears there is no traffic after PIFS time gap, it sends out beacon frame Field to indicate length of time that PCF (polling) will be used sort of of DCF (contention) during this time.(Stalling,2008)receiving stations must stop transmission for that amount of timeThe layover during which PCF operates is called the contention- escaped blockage (CFP). Before the CFP begins, the AP operates under DCF, but it makes use of the priority inter-frame space (PIFS) to take hold the medium, and then sends out a beacon packet containing the duration of the CFP.(Stalling,2008)Figure (5). combination DCF PCF .(Stalling,2008)The fragmentation operation in PCF is same as DCF,but in PCF conation free period making different ,but because the DCF working with joust period (CP) and PCF working with Contention free period(CFP) . (Yuguang Kwon,2003 ).There are some limitations on PCF which directly effetely the fragmentation, one of these limitation is the binary star program exponential back absent , the frame need to wait even the medium is free ,because the binary exponential back off will double the random number from 15 to 1023 till the medium will be free, so this can effect the impart the frame in fragmentation .Other limitation in PCF has been intentional to support time-limitedfor poor QoS performance. In particular the central pooling scheme is uneconomical and complex which causes fall of the performance of PCF high-priority traffic under load, when a free station is allowed to send a frame of length between 0 and 2346 bytes, it introduce the difference of transmission time. (Dillip.2006).2.1.0)Analysis The earliest work in data fragmentation IEEE802.11In this section we will analysis ,In this paper(Abhishek,2003) we can analysis that polling in PCF causes overhead . In PCF, point coordinator (PC )is a central coordinator that schedules channel access for all other polling able stations in CFP. PC maintains list of poll able nodes in BSS. At beginning of CFP it survey all stations in Round Robin fashion. Nodes receiving poll serve back, either by transmitting data or there is no data frame. If station has no unfinished data, then it sends no frame. If station fails to do either then its result in polling time out at PC and PC resumes polling. When most stations have pending data, in monastic order polling provide to ordered channel access and this can reduces collisions. But when few stations have pending data and perch are silent, this polling operation becomes study(ip) overhead, It adds unnecessary delay for stations with data, ascribable to unsuccessful poll attempts for stations, with no pending data. For this reason resulting in throughput decreasing. construct the figure(6) we compares the overall throughput of network with 32 and 64 nodes having 16 nodes that have data to transmit. W e can analysis that Effect of polling overhead is clearly visible(Abhishek,2003)Figure 6 the effect of (polling overhead )on network throughputFrom this paper, we can find the solution for permeable paper (Abhishek ,2003),by analysis that the overhead in PCF fragmentation is high ,so sort of of allowing the transmission of multiple packets with a high data rate ,its workable to make MPDU large size to reduce the overheads caused by multiple packets transmission when channel condition is dependable. In Literature Review analysis we can describe it more clear(Yuguang and Kwon,2003 ).As we understand from this paper, that voice packets transmitted by use of PCF mode ,According to our analysis, PCF mode can well support packetized voice transmission using echo canceller fragmentation ,when the load are fragmented into small packets ,large fragment size such as 2000 or 2304 bits point favour to voice traffic at the available bandwidth for data transmission.(Xiyan,al.,2003)In this p aper ,we can analysis that, they propose a saucily rate adaptive MAC protocol with adynamic fragmentation. The major advance is the use of multiple fragmentation thresholds, for different rates to generate a new fragment from (remaining) MSDU only after the rate for next transmission is selected. With this scheme, the nodes with good channels can transmit more data than the ones with bad channel.( Byung,al.,2005)In this paper ,several methods been used to improve wireless network performance ,the result indicate as we can see in the figure (7),that the effect of fragmentation threshold can increase throughput and improve the wireless network performance, but how, the answer is when the bit error rate selected to be and the fragmentation threshold to be 256 bytes or 512 bytes, the result show that there is no any major effect on the network performance.(Walid Ajlouni,2006)figure (7),Effect of fragmentation, ( Walid Naim,2006)This paper ,proposes an adaptive control algorithm to tun e the performance of IEEE802.11wireless LANs, so that traffic demands with different characteristics will be handled mostly by the MAC protocol that fits them. The algorithm aims is control the percentage of CFP duration within a super frame by measuring the throughput in PCF mode.(James,al.,2003)Chapter 3 Literature Review analysisT In this section we will be analysis ( 3.1 he out come from literature Review analysis-Fragmentation It is the process of breaking apart a packet into smaller pieces. Fragmentation is process that dividing long frame to several shorter frame, Each fragment consists of a MAC Layer header, frame check sequence (FCS), and a fragment number indicating its ordered position within the frame. (Yuguang Kwon,2003 ).-The main reason we are using fragmentation is because the Wireless LANs have high bit error rates.-The period during which PCF operates is called the contention-free period (CFP). When most stations have pending data, in order polling provide ordered channel access and reduces collisions. But when few stations have pending data and rest are silent, this polling mechanism becomes major overhead, It adds unnecessary delay for stations . There are some limitations on PCF which directly effetely the fragmentation, one of these limitation is the binary exponential back off , the frame need to wait even the medium is free ,because the binary exponential back off will double the random number from 15 to 1023 till the medium will be free, so this can effect the retransmit the frame in fragmentation .(Class lecture ,Simulation Network Multimedia)3.2 ) What will be solutions for Some Of above problems1) When there will be high overhead in PCF fragmentation is, so instead of allowing the transmission of multiple packets with a high data rate ,its accomplishable to make MPDU large size to reduce the overheads caused by multiple packets transmission when channel condition is good.2) when the bit error rate selected to be or the fragmentati on threshold to be 16 bytes or 256 bytes, the result show that there is no any major effect on the network performance, so this maybe will be one of in our design and try out we will select the above bit rat error than bogus it and observe the result.( Walid Naim,2006)3) We go for IEEE 802.11e which introduces new coordination function called as a hybrid Coordination Function (HCF) that is only useful for QoS network. The HCF supports channel access mechanisms, Enhanced Distributed ship two additional Access (EDCA) for contention-based and HCF Coordination Channel Access (HCCA) for contention-free. And this stander will run all problem with Polling and CW, which effect on fragmentation in PCF.) Future Work3.3During my research i found that there is new standard been developed in 2007 , it know as IEEE 802.11e. To the best of our knowledge, there is actually little literature , that serve ups with polling overhead in PCF .Other People have mentioned the problem earlier and th ere also come with some proposed solution to deal with it. also that people have mention the importance of polling for providing QoS service in IEEE 802.11 WLAN. New upcoming standard for QoS, IEEE 802.11e its called HCF (Byung,al.,2005)Chapter 4 Research ProblemAs i mention earliest the reason of selecting the study of data fragmentation effect in IEEE 802.11 under PCF mode is , is because in my organization they are looking for wireless network technology ,which can provide such applications like for delivering traffic for real-time applications such as Voice and data.There are some limitations on PCF which directly effetely the fragmentation, one of these limitation is the binary exponential back off , the frame need to wait even the medium is free ,because the binary exponential back off will double the random number from 15 to 1023 till the medium will be free, so this can effect the retransmit the frame in fragmentation .There for i found that IEEE 802.11 under PCF mode ,will not satisfy myChapter 5 Design and Experiment SetupIn This section i will be doing simulation , by using OPNET computer software as we can see in figure (8) to design and valuate the performance of the IEEE 802.11 MAC protocol for wireless LANs. The aim of the project is to study the effect of data fragmentation in IEEE802.11under PCF mode. The main objectives of this experiment is toStudy the effect of data fragmentation in PCF by choosing different bit rate error and observe the major effect on the network, as we analysis that using low bit error rate ,and give fragmentation value 256 bytes or 512bytes ,the result must show that there will be will no effect on the data transmission or on network performance. We can also do measuring response time (seconds) for PCF with 256 fragmentation and fixed data rate 5.5Mbps, and for page response time (seconds) for PCF with 256 fragmentations with fixed data rate 11Mbps.Finaly correspond the result obtain.Figure 8 WLAN Setup diagram in O PNETChapter 6 ConclusionDuring my working in this project I have identify the effect of data fragmentation in IEEE802.11 under PCF in wireless network. I come out that this standard will help me in my organization to be used in library slur only.The probability of lost frame is much higher for wireless links. Thats why fragmentation is used to Reduces amount of time medium is in use and Reduces probability of collisions .The IEEE 802.11 WLAN has two different channel accessing mechanisms, namely, the distributed coordination function (DCF) and point coordination function (PCF).We understand that When most stations have pending data, nonparallel polling provide ordered channel access and reduces collisions. But when few stations have pending data and rest are silent, this polling mechanism becomes major overhead, It adds unnecessary delay for stations with data.Also we understand that when there will be high overhead in PCF fragmentation is, so instead of allowing the transmission of multiple packets with a high data rate ,its possible to make MPDU large size to reduce the overheads caused by multiple packets transmission when channel condition is good.Anew standard has been developed in 2007 , it know as IEEE 802.11e. which support QoS. and can solve polling overhead in PCF.The ReferencesBooks Stalling,W.William.,2008.Data and computer communications 8 ed published by Dorling Kindersly(India) Pvt,LTD 482, F.I.E Delhi, India.Stalling, W,Willim., 2008, Wirless communications Network second ed published by Asoke K. Ghosh (India) Delhi, India.E-BooksRoss, John.,2008. Book of Wireless A Painless Guide to Wi-Fi and Broadband Wireless (2nd Edition).San Francisco, CA, USA No stiffen Press, Incorporated, p 15.Available athttp//site.ebrary.com/lib/caledonian/docDetail.action?docID=10218384p00=a%20painless%20guide%20wi-fi%20broadband%20wireless%20(2nd%20edition).Journal PapersTamer, M Samir ,K .,2009.Performance Analysis of Wireless Local force field Networks ,WLA Ns A thesis submitted to the competency of Engineering at Cairo University in partial fulfillment of the requirement for the degree ofMASTER OF SCIENCE.Yoon Hougwon Kim Jeonge. ,2003. 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College of Information TechnologyUniversity. emailprotected .UAEJames X.Dong,S.,2004 Mustafa Ergen Improving the Aggregate Throughput of Access Points in IEEE 802.11Wireless LANs, and Anuj Puri Department of Electrical Engineering Computer Science University of California at Berkeley.Ziouva E. and Antonakopoulos T.2003., Efficient Voice Communications over IEEE802.11 WLANs Using Improved PCF Procedures.Walid ,HNaim ,A.,2006 Performance Enhancement of Wireless Local Area Networks,Dept. of Computer Science,Amman Arab University for Graduate Studies,P 0 Box 2925, Amman 11821, Jordan.Web PageURLhttp//msdn.microsoft.com/en-us/library/ff556962(VS.85).aspx