The Media Access Delay Information Technology Essay

The Media approach path Delay Information Technology proveOPNET Modeller is the profits development softw atomic number 18. OPNET permits design and learn communication nets, devices, protocols, and application. OPNETs object-oriented moulding stylishness and graphical user interface (GUI) let easy of growing models from the real world entanglement, hardware devices, and protocols. Modeller supports all major network forms and technologies, permitting you to design and test discordant situations. (Opnet)IntroductionI bring on deliberated various Medium main course Control ( macintosh) protocols for Wireless(prenominal) local Area (Wlocal area network) Networks. To consider the best one surrounded by the existing protocols, it is necessary to have a network model scenario and some performance metrics on the basis of which they put forward be assessed. In this paper, various metrics for comparing the performance of MAC protocols and a network model to carry expose pretenc e is discussed. At the end of this chapter, results obtained from the example in the form of graphs leave alone be presented.DCFEDCFMetricsPicking the correct metrics or parameters in the evaluation of the QoS ( eccentric of Service) chemical mechanisms is vital to the result and rationality of the evaluation. The metrics employ are Throughput, approach shot Delay, and End to End Delay in case of real measure mul fourth dimensiondia merchandise resembling VoIP, Video streaming (Video conferencing), response time in case of Telnet or Remote Login type applications which cannot tolerate determine and loss of data. Retransmission Attempts in case a lieu does not pull in a chance collect to internal encounter. The following list beneath is the item of metrics usedThroughputThe Throughput for diverse antecedence levels shows how rise the QoS schemes can provide service differentiation between the various priorities. The Throughput of all station shows the utilization of the wireless medium. Wireless bandwidth is a scarce resource, so businesslike use of it is vital.Media admittance DelayWe measure access clasp as the time from when the data reaches the MAC layer until it is successfully transmitted come out of the closet on the wireless medium. The reason for studying average access learn is that many real-time applications have a maximum tolerable delay, subsequently which the data will be useless. Therefore, it is important to provide low delay for real-time flows.Retransmission AttemptsTotal number of Retransmission Attempts by all Wireless local Area Network MACs in the network until either packet is successfully transmitted or it is discarded as a result of hit short or long retry limit. For 802.11e-capable MACs, the Retransmission Attempt counts recorded down the stairs this statistic also include retry count increments collectible to internal collisions. This mover plays important role in Performance of WLAN. entropy Dropped info Dropped due to unavailability of access to medium. This factor largely affects the reliability of WLAN.Simulation ScenarioCreating a simulation scenario that is corresponding to real world scenario is the premier step of simulation. In this simulation, the wireless topology consisted of several wireless displace and one subject station in the wireless LAN. The base station was connected to a wired node ( recruit 2.1) which serves as a sink for the flows from the wireless domain. all in all wireless stations are located such that every station is able to detect a transmission from any other station, and there is no mobility in the system. This core our results will not be impact by mobility and phenomenon such as the hidden node problem.Figure 2.1 Wi-Fi network modelsThe simulation experiments are carried out using OPNET Simulator version 9.1 on Windows XP SP3. For this simulation, a data rate of 11 Mbps is chosen. Various MAC and PHY (Physical Layer of OSI) parameter values u sed in our experiment are match to IEEE 802.11e nonpayment values given in flurry 2.1. We have run the simulation for 5 proceedings for each scenario, and so compared the results obtained from them. Figure 2.1 shows a network model for the experiment.Table 2.1 MAC and PHY parameter values used in ExperimentATTRIBUTEVALUEPhysical CharacteristicsDirect Sequence information Rate (bps)11 MbpsTransmit Power (W)0.005Buffer Size (bits)256000BSS Identifier cable car AssignedChannel settingsAuto AssignedRoaming CapabilityDisabledAP shine Interval (secs)0.02Large Packet ProcessingDropSimulation methodTo compare the performance of DCF (Distributed Coordination Function) and EDCF (Enhanced Distributed Coordination Function) two scenarios were created medium access in first scenario was supported by DCF and in second, EDCF protocol was used at the MAC layer. Network environment factors which were used as a benchmark set up same for twain scenarios. Detailed specifications are given in th e Table 2.1 showing the MAC and PHY parameters used in experiment. The performance evaluation is through with(p) by simulating both scenarios one by one in OPNET simulator and hence comparing the graphs obtained.ResultsAfter choosing metrics, the simulation is done for 5 minutes for a scenario. Then results were gathered. compendium of EDCFIn case of EDCF, all four work classes were fed into the MAC layer from gameer layer, which are corresponding to AC (0), AC (1), AC (2) and AC (3) respectively to check how efficient the overbold protocol is to provide service differentiation required for real time application. (Note that DCF does not support service differentiation, so no provision of addition category). For this, in the application visibility of scenario (for EDCF protocol) different application was con protruded for different access category. Details are shown in the Table 4.1.Table 4.1 Access Category corresponding to an applicationACCESSCATEGORYAPPLICATION pieceDESIGNAT IONAC(0)HTTP (LIGHT)BACKGROUNDAC(1)REMOTE LOGIN (HEAVY)EXCELLENT EFFORTAC(2)VIDEO CONFERENCING synergetic MULTIMEDIAAC(3)VOIPINTERACTIVE VOICEIn the profile configuration, a profile for clients was configured that uses all the four applications. In simulation scenario, 15 stations were configured to use these services randomly. In the simulation, we assumed that each traffic class has the equal portion of the total data traffic in terms of the average number of packets generated per unit time. The results obtained are as followsThroughput of different Access CategoriesFigure 4.2 Throughputs of Different Access CategoriesIt is observed from figure 4.2 that the Throughput of Access category 3 is way high than the Access category 0 and 1. Throughput for Access category 2 lies in between 3 and 1. It means that Throughput for applications like Voice over IP and Video conferencing, EDCF provides maximum Throughput by providing them more than priority over the other services like fair HTTP.Media Access Delay for Different Access CategoriesFigure 4.3 Wireless LAN Media Access DelayIt is observed from figure 4.3 that the Media Access Delay for Access category 3 is at minimum among all Access categories. Media Access Delay for Access category 2 is just 3 to 4 seconds more than AC (3). It means that the medium is assigned to the application according to the priority. Thus, EDCF provides lesser Medium Access Delay for real-time applications.Comparative Analysis of DCF and EDCFNext step is to check the performance of both protocols in terms of Throughput, Media Access Delay, Retransmission Attempts and Data Dropped. These four metrics are determining factors in terms of overall performance of both the protocols.ThroughputFigure 4.4 Throughput of DCF vs. EDCFIt is observed from figure 4.4 that in the first 30 seconds of simulation, Throughput of both DCF and EDCF is high, but then later that, it decreases with time and stabilizes for both protocols. Throughput in firs t 30 seconds is high due to less number of Retransmission Attempts (less number of backoffs). From Graph analysis, one fact is clear visible, that curve of DCF is marginally higher than that of EDCF. We can conclude that DCFs overall Throughput is fairly more than the EDCF.Retransmission AttemptsFigure 4.5 Retransmission Attempts of DCF vs. EDCFIt is observed from figure 4.5 that in the first 30 seconds of simulation, Retransmission Attempts for both DCF and EDCF are less, but then after that, it decreases with time and stabilizes for both protocols. Retransmission Attempts in first 30 seconds are less due to less number of backoffs assigned to wireless stations. There is a small detectable difference between curves of Retransmission Attempts of DCF and EDCF protocol. That small difference implies that the overall Retransmission Attempts made in DCF protocols are a bit lesser than EDCF protocol.Media Access DelayFigure 4.6 Media Access Delay of DCF vs. EDCFIn Figure 4.6, for the first minute of simulation the Medium Access Delay for both protocols increases at equal pace, and then after that, DCF suffers somewhat lesser Access Delay than EDCF. The increase in the Medium Access Delay for both protocols is due to increase in the number of nodes competing to gain access of medium.Data DroppedFigure 4.7 amount of Data Dropped of DCF vs. EDCFIt is observed from figure 4.7 that the first 30 seconds of simulation, DCF suffers a sudden high Data Drop, but Data Drop in EDCF increases gradually. The reason of alter Data Drop gradually in EDCF is the service differentiation which provides priority based scheme to handle different kind of data. After 2.5 minutes of simulation, curves of Data Dropped of DCF and EDCF remain same for both protocols, EDCF finishes at less Data Dropped than DCF.ConclusionsConclusionThe results obtained from simulation shows that Enhanced Distribution Coordination Function provides efficient mechanism for service differentiation and hence p rovides part of service to the Wireless LAN. However, this onward motion comes at a cost of a decrease in quality of the overthrow priority traffic up to the point of starvation. The acquisition of the radio set 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. But in terms of Quality of Service for real-time applications (like Video conferencing) EDCF outperforms DCF.EDCF has been purposed as the medium access keep protocol for IEEEs upcoming standard IEEE 802.11e. Presently, all of the wireless devices use DCF as the default MAC protocol an d PCF as the optional functionality.