Network WLAN Report

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TABLE OF CONTENT

ABSTRACT ......................................................................................................................................3

INTRODUCTION .............................................................................................................................3

OBJECTIVE .....................................................................................................................................3

OVERVIEW .....................................................................................................................................3

LAB SPECIFICATIONS ......................................................................................................................4

LAB SIMULATION ...........................................................................................................................5

A. NETWORK DESIGN .....................................................................................................................5

SCENARIO 1 DCF: ...........................................................................................................................5

SCENARIO 2 DCF_FRAG: ................................................................................................................5

SCENARIO 3 DCF_PCF: ....................................................................................................................5

SCENARIO 4 DCF_PCF_FRAG: ..........................................................................................................5

B. LAB RESULTS ..............................................................................................................................5

SCENARIO 1 AND 2 .........................................................................................................................5

SCENARIO 3 AND 4 .........................................................................................................................6

ANSWERS ......................................................................................................................................6

CONCLUSION .................................................................................................................................8

REFERENCES ..................................................................................................................................9

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ABSTRACT

The main purpose of this report is to discuss the laboratory exercises which based on the MAC (Medium Access Control) sub layer of the IEEE 802.11 standard for WLAN (wireless local area network). The labs have been stimulated in OPNET IT Guru Academic simulation environment, which will be conducted to demonstrate and construct different network scenarios. INTRODUCTION IEEE 802.11 MAC protocol is a standard for wireless local area networks (LANs), and has also been implemented in many network simulation packages for wireless multi-hop ad hoc networks. However, it is well known that, as the number of active stations increases, the performance of IEEE 802.11 MAC in terms of delay and throughput degrades dramatically, especially when each stations load approaches its saturation state. To explore the inherent problems in this protocol, it is important to characterize the probability distribution of the packet service time at the MAC layer. OBJECTIVES This lab addresses the Medium Access Control (MAC) sublayer of the IEEE 802.11 standard for the wireless local area network (WLAN). Various options of this standard are studied in this lab. The performance of these options is analyzed under multiple scenarios. OVERVIEW The IEEE 802.11 standard provides wireless connectivity to computerized stations that require rapid deployment, such as portable computers. The Medium Access Control (MAC) sublayer in the standard includes two fundamental access methods: distributed coordination function (DCF) and point coordination function (PCF). DCF utilizes the carrier sense multiple access with collision avoidance (CSMA/CA) approach. DCF is implemented in all stations in the wireless local area network (WLAN). PCF is based on polling to determine the station that can transmit next. Stations in an infrastructure network optionally implement the PCF access method. In addition to the physical CSMA/CA, DCF and PCF utilize a virtual carrier-sense mechanism to determine the state of the medium. This virtual mechanism is implemented by means of the network allocation vector (NAV), which provides each station with a prediction of future traffic on the medium. Each station uses NAV as an indicator of time periods during which transmission will not be initiated even if the station senses that the wireless medium is not busy. NAV gets the information about future traffic from management frames and the header of regular frames being exchanged in the network. With DCF, every station senses the medium before transmitting. The transmitting station defers as long as the medium is busy. After deferral and while the medium is idle, the transmitting station has to wait for a random back off interval. After the back off interval and if the medium is still idle, the station initiates data transmission or optionally exchanges request to send (RTS) and clear to send (CTS) frames with the receiving station. The effect of RTS and CTS frames will be studied in the Mobile WLAN lab. With PCF, the access point (AP) in the network acts as a point coordinator (PC). The PC uses polling to determine which station can initiate data transmission. It is optional for the stations in the network to

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participate in PCF and hence respond to polls received from the PC. Such stations are called CF-Pollable stations. The PCF requires the PC to gain control of the medium. To gain such control, the PC utilizes the The standard allows for fragmentation of the MAC data units into smaller frames. Fragmentation is favorable in case the wireless channel is not reliable enough to transmit longer frames. Only frames with a length greater than a fragmentation threshold will be fragmented. Each fragment will be sent independently and will be separately acknowledged. During a contention period, all fragments of a single frame will be sent as bursts with a single invocation of the DCF medium access procedure. In case of PCF and during a contention-free period, fragments are sent individually following the rules of the point coordinator (PC). LAB SPECIFICATIONS:

- 09 wlan_station_adv (fix) with the following properties:

Configuring the wireless nodes:

Node Name Destination Address Wireless LAN MAC Address

Node_0 Random Auto

Node_1 5 1

Node_2 8 2

Node_3 6 3

Node_4 7 4

Node_5 1 5

Node_6 3 6

Node_7 4 7

Node_8 2 8

Traffic Generation Parameters for all nodes (except node_0) Start Time (seconds) = constant(2) ON State Time (seconds) = exponential(4) OFF State Time (seconds) = exponential(4) Packet Generation Arguments

Interval time (seconds) = exponential(0.06)

Packet size (bytes) = uniform (500,1500)

Segmentation size (bytes) = No segmentation

Wireless LAN Parameters (node_0 only) Buffer size (bits) = 4608000

- Results to collect:

Global Statistics Wireless LAN

Delay (sec)

Load (bit/sec)

Throughput (bits/sec)

Node Statistics Wireless lan

Delay (sec)

Retransmission Attempts (packets)

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LAB SIMULATION A. NETWORK DESIGN

a. SCENARIO 1: DCF In the scenario 1, only the node_0 has been set as the Access Point Functionality in the network

b. SCENARIO 2: DCF_FRAG In this scenario, we will allow fragmentation of the MAC data units into smaller frames and test it effect on the network performance.

c. SCENARIO 3: DCF_PCF

The DCF_PCF scenario will utilizes the point coordination function (PCF) method for the MAC sublayer along with the DCF method.

d. SCENARIO 4: DCF_PCF_FRAG Lastly, the DCF_PCF_Frag scenario, we will allow fragmentation of the MAC data and check its effect along with PCF.

B. LAB RESULTS This is a very important part of the lab simulation process where we can explore and compare between different networks configuration based on the statistics that we collect from the simulation software. For our simulation we set the simulation time to 10 minutes maximum and run the simulation of the two scenarios (1 & 2) simultaneously. At the end of the simulation we got the results as follow: Scenario 1 and 2 (DCF and DCF_Frag)

In a comparison of both DCF and DCF_Frag:

- The DFC seems to have lower delay time than the DCF_Frag. - The Load of the DCF_Frag supposes to be higher than DCF. - The result of the wireless throughput of DCF is far greater than DCF_Frag.

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Scenario 3 and 4 (DCF_PCF and DCF_PCF_FRAG)

In comparison of scenario 3 and 4, we have noted the below results:

- DCF_PCF_Frag Wireless LAN Delay(sec) is higher than DCF_PCF. - DCF_PCF Wireless LAN Load (bits/sec) is greater than DCF_PCF_Frag - Throughput of DCF_PCF is far better than DCF_PCF_Frag

ANSWERS 3. The graphs below have been comparing, node 3 has PCF enabled and node 2 does not. First, you can then see the effect PCF has on both LAN Delay and Retransmission attempts in the PCF_DCF scenario. Node 3 has fewer delays and retransmissions because the PCF knows which station can transmit next allowing for fewer delays and fewer collisions.

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4. compare the DCF_PCF scenario to the new scenarios that we have just created, there are a lot of changes in delay times. However, after added more PCF to enabled Wireless LAN stations, the delay traffic is dramatically lower than the other scenarios. What is more, the Load traffic seems to stay in the middle relatively compare to another. In the last graph showing throughput, it is quite clear that as the number of PCF stations increases on throughput. This is due again to the concept that these stations already have information as to which stations to transmit to next saving time spend configuring routes.

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CONCLUSION OPNET IT Guru Academic software is very tool for the networks engineers especially for the students to quickly design, simulate and analyze the results of the networks before deploy it to the real work. Follow by the results and graphs obtained from the OPNET Guru software, we compare the results from the scenario1 (DCF) to the last 5 scenarios on Delay, Load and throughput. Remarkably, the Delay and Load traffic go up while the nodes have applied the Fragment. However, the Throughput traffic seems to be greater. Another remarkable change is that when the scenario has been applied both DCF_PCF with all the nodes have been enabled. The delay traffic is dramatically lower than the other scenarios. What is more, the Load traffic seems to stay in the middle relatively compare to another. Furthermore, the throughput traffic looks greater than the rest scenarios. In short, I would like to express that the scenario DCF_allPCF is the best scenario in applying WLAN.

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REFERENCES:

1. WHAT IS WLAN? http://en.wikipedia.org/wiki/WLAN

2. WHAT IS IEEE 802.11? http://en.wikipedia.org/wiki/IEEE_802.11

3. WHAT IS DCF? PCF? http://en.wikipedia.org/wiki/Distributed_Coordination_Function

Documents

Network WLAN Report