The Media Access Delay Information Technology Essay

OPNET Modeller is the web development package. OPNET permits design and learn communicating webs, devices, protocols, and application. OPNET ‘s object-oriented modeling chic and graphical user interface ( GUI ) let easy of developing theoretical accounts from the existent universe web, hardware devices, and protocols. Modeller supports all major web signifiers and engineerings, allowing you to plan and prove assorted state of affairss. ( Opnet )


I have deliberated assorted Medium Access Control ( MAC ) protocols for Wireless local Area ( WLAN ) Networks. To take the best 1 surrounded by the bing protocols, it is necessary to hold a web theoretical account scenario and some public presentation prosodies on the footing of which they can be assessed. In this paper, assorted prosodies for comparing the public presentation of MAC protocols and a web theoretical account to transport out simulation is discussed. At the terminal of this chapter, consequences obtained from the simulation in the signifier of graphs will be presented.

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Picking the right prosodies or parametric quantities in the rating of the QoS ( Quality of Service ) mechanisms is critical to the consequence and reason of the rating. The prosodies used are Throughput, Access Delay, and End to End Delay in instance of real-time multimedia traffic like VoIP, Video cyclosis ( Video conferencing ) , response clip in instance of Telnet or Remote Login ; type applications which can non digest hold and loss of informations. Retransmission Attempts in instance a station does non acquire a opportunity due to internal hit. The undermentioned list below is the point of metric ‘s used:


The Throughput for different precedence degrees shows how good the QoS strategies can supply service distinction between the assorted precedences. The Throughput of all Stationss shows the use of the radio medium. Wireless bandwidth is a scarce resource, so efficient usage of it is critical.

Media Access Delay

We measure entree hold as the clip from when the information reaches the MAC bed until it is successfully transmitted out on the radio medium. The ground for analyzing mean entree hold is that many real-time applications have a maximal tolerable hold, after which the information will be useless. Therefore, it is of import to supply low hold for real-time flows.

Retransmission Attempts

Entire figure of Retransmission Attempts by all Wireless Local Area Network MACs in the web until either package is successfully transmitted or it is discarded as a consequence of making short or long retry bound. For 802.11e-capable MACs, the Retransmission Attempt counts recorded under this statistic besides include retry count increases due to internal hits. This factor plays of import function in Performance of WLAN.

Data Dropped

Data Dropped due to inaccessibility of entree to medium. This factor mostly affects the dependability of WLAN.

Simulation Scenario

Making a simulation scenario that is matching to existent universe scenario is the first measure of simulation. In this simulation, the radio topology consisted of several wireless Stationss and one base station in the radio LAN. The base station was connected to a wired node ( Figure 2.1 ) which serves as a sink for the flows from the radio sphere. All wireless Stationss are located such that every station is able to observe a transmittal from any other station, and there is no mobility in the system. This means our consequences will non be impacted by mobility and phenomenon such as the concealed node job.

Figure 2.1 Wi-Fi web theoretical accounts

The simulation experiments are carried out utilizing OPNET Simulator version 9.1 on Windows XP SP3. For this simulation, a information rate of 11 Mbps is chosen. Assorted MAC and PHY ( Physical Layer of OSI ) parametric quantity values used in our experiment are harmonizing to IEEE 802.11e default values given in Table 2.1. We have run the simulation for 5 proceedingss for each scenario, and so compared the consequences obtained from them. Figure 2.1 shows a web theoretical account for the experiment.

Table 2.1: MAC and PHY parametric quantity values used in Experiment



Physical Features

Direct Sequence

Data Rate ( bits per second )

11 Mbps

Transmit Power ( W )


Buffer Size ( spots )


BSS Identifier

Car Assigned

Channel scenes

Car Assigned

Rolling Capability


AP Beacon Interval ( secs )


Large Packet Processing


Simulation Method

To compare the public presentation of DCF ( Distributed Coordination Function ) and EDCF ( Enhanced Distributed Coordination Function ) two scenarios were created ; average entree in first scenario was supported by DCF and in 2nd, EDCF protocol was used at the MAC bed. Network environment factors which were used as a benchmark configured same for both scenarios. Detailed specifications are given in the Table 2.1 demoing the MAC and PHY parametric quantities used in experiment. The public presentation rating is done by imitating both scenarios one by one in OPNET simulator and so comparing the graphs obtained.


After taking prosodies, the simulation is done for 5 proceedingss for a scenario. Then consequences were gathered.

Analysis of EDCF

In instance of EDCF, all four traffic categories were fed into the MAC bed from higher bed, which are matching to AC ( 0 ) , AC ( 1 ) , AC ( 2 ) and AC ( 3 ) severally to look into how efficient the new protocol is to supply service distinction required for existent clip application. ( Note that DCF does non back up service distinction, so no proviso of Access class ) . For this, in the application profile of scenario ( for EDCF protocol ) different application was configured for different entree class. Detailss are shown in the Table 4.1.

Table 4.1 Access Category matching to an application






AC ( 0 )



AC ( 1 )


Excellent EFFORT

AC ( 2 )



AC ( 3 )



In the profile constellation, a profile for clients was configured that uses all the four applications. In simulation scenario, 15 Stationss were configured to utilize these services indiscriminately. In the simulation, we assumed that each traffic category has the equal part of the entire information traffic in footings of the mean figure of packages generated per unit clip. The consequences obtained are as follows:

Throughput of Different Access Categories

Figure 4.2 Throughputs of Different Access Categories

It is observed from figure 4.2 that the Throughput of Access class 3 is manner high than the Access class 0 and 1. Throughput for Access class 2 lies in between 3 and 1. It means that Throughput for applications like Voice over IP and Video conferencing, EDCF provides maximal Throughput by supplying them more precedence over the other services like simple HTTP.

Media Access Delay for Different Access Categories

Figure 4.3 Wireless LAN – Media Access Delay

It is observed from figure 4.3 that the Media Access Delay for Access class 3 is at lower limit among all Access classs. Media Access Delay for Access class 2 is merely 3 to 4 seconds more than AC ( 3 ) . It means that the medium is assigned to the application harmonizing to the precedence. Therefore, EDCF provides lesser Medium Access Delay for real-time applications.

Comparative Analysis of DCF and EDCF

Following measure is to look into the public presentation of both protocols in footings of Throughput, Media Access Delay, Retransmission Attempts and Data Dropped. These four prosodies are finding factors in footings of overall public presentation of both the protocols.


Figure 4.4 Throughput of DCF vs. EDCF

It is observed from figure 4.4 that in the first 30 seconds of simulation, Throughput of both DCF and EDCF is high, but so after that, it decreases with clip and stabilizes for both protocols. Throughput in first 30 seconds is high due to less figure of Retransmission Attempts ( less figure of backoff ‘s ) . From Graph analysis, one fact is clearly seeable, that curve of DCF is marginally higher than that of EDCF. We can reason that DCF ‘s overall Throughput is slightly more than the EDCF.

Retransmission Attempts

Figure 4.5 Retransmission Attempts of DCF vs. EDCF

It is observed from figure 4.5 that in the first 30 seconds of simulation, Retransmission Attempts for both DCF and EDCF are less, but so after that, it decreases with clip and stabilizes for both protocols. Retransmission Attempts in first 30 seconds are less due to less figure of backoff ‘s assigned to wireless Stationss. There is a little noticeable difference between curves of Retransmission Attempts of DCF and EDCF protocol. That little difference implies that the overall Retransmission Attempts made in DCF protocols are a spot lesser than EDCF protocol.

Media Access Delay

Figure 4.6 Media Access Delay of DCF vs. EDCF

In Figure 4.6, for the first minute of simulation the Medium Access Delay for both protocols additions at equal gait, and so after that, DCF suffers slightly lesser Access Delay than EDCF. The addition in the Medium Access Delay for both protocols is due to increase in the figure of nodes viing to derive entree of medium.

Data Dropped

Figure 4.7 sum of Data Dropped of DCF vs. EDCF

It 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 additions bit by bit. The ground of changing Data Drop bit by bit in EDCF is the service distinction which provides precedence based strategy to manage different sort of informations. After 2.5 proceedingss of simulation, curves of Data Dropped of DCF and EDCF remain same for both protocols, EDCF finishes at less Data Dropped than DCF.



The consequences obtained from simulation shows that Enhanced Distribution Coordination Function provides efficient mechanism for service distinction and hence provides quality of service to the Wireless LAN. However, this betterment comes at a cost of a lessening in quality of the lower precedence traffic up to the point of famishment. The acquisition of the wireless channel by the higher precedence traffic is much more aggressive than for the lower precedence. Higher precedence traffic benefited, while lower precedence traffic suffered.

In footings of overall public presentation ( under the used simulation conditions in this peculiar survey of QoS of Wireless LAN ) , DCF performs marginally good than EDCF. This happens due to ground that in EDCF mechanism, each AC map Acts of the Apostless like a practical station for medium entree, so more hit will be expected for EDCF scenario. But in footings of Quality of Service for real-time applications ( like Video conferencing ) EDCF outperforms DCF.

EDCF has been purposed as the medium entree control protocol for IEEE ‘s approaching criterion IEEE 802.11e. Soon, all of the radio devices use DCF as the default MAC protocol and PCF as the optional functionality.