Simulation of SFU Wi-Fi using Riverbed Modeler

by

Shaganroop Kaur

B.Tech, Punjab Technical University, 2016

Project Submitted in Partial Fulfillment of the

Requirements for the Degree of

Master of Engineering

in the

School of Engineering Science

Faculty of Applied Sciences

© Shaganroop Kaur 2019

SIMON FRASER UNIVERSITY

Spring 2019

Copyright in this work rests with the author. Please ensure that any reproduction or re-use is done in accordance with the relevant national copyright legislation.

ii

Approval

Name: Shaganroop Kaur

Degree: Master of Engineering

Title: Simulation of SFU Wi-Fi using Riverbed Modeler

Supervisory Committee: Chair: Michael Adachi Assistant Professor

Ash M Parameswaran Senior Supervisor Professor

Balbir (Bob) Gill Supervisor Limited Term Lecturer

Date Defended/Approved: April 24, 2019

iii

Abstract

Pervasive in the workplace, the home, educational institutions, café, airports, and street

corners, wireless networks are now one of the most important access network

technologies on the Internet today. The IEEE has standardized the 802.11 protocol for

wireless local area networks. This project involves the study of the SFU wireless LAN to

understand the problem of the slow wireless network (e.g. problems with top hat

quizzes, congestion of devices, etc.).The wireless profile in the academic quadrangle

area in various classrooms(AQ3181, AQ3182) and hallways will be studied. The Xirrus

WiFi inspector and WirelessMon will be used to check the Wi-Fi network and to gather

information about the wireless access point(signal strength, data rate, sent rate, etc.).

The scenario of the lecture halls with a high-density network will be simulated in the

Riverbed modeler to find out the network issues and the solution for the same.

Keywords: 802.11; Riverbed Modeler

iv

Acknowledgements

I would like to take this opportunity to thank my supervisor, Dr. Ash M. Parameswaran

for giving me an opportunity to work on the project under his supervision. I would also

like to thank my project instructor Mr. Balbir Gill for his ideas and, full guidance and

support during the project. A special thanks to Simon Fraser Engineering sciences

department for making it all happen. Also, I thank Dr. Michael Adachi for agreeing to

chair the committee on such short notice. I appreciate everyone who has directly or

indirectly contributed towards the project.

v

Table of Contents

Approval ............................................................................................................................ ii Abstract ............................................................................................................................. iii Acknowledgements .......................................................................................................... iv Table of Contents .............................................................................................................. v List of Tables .................................................................................................................... vi List of Figures................................................................................................................... vii List of Acronyms .............................................................................................................. viii

Chapter 1. Introduction ................................................................................................ 1

Chapter 2. Wi-Fi Literature Review ............................................................................. 3 2.1. Wi-Fi Technology overview ..................................................................................... 3 2.2. Wi-Fi Channels ........................................................................................................ 6 2.3. WLAN overview ....................................................................................................... 7

2.3.1. Wi-Fi Radio topology ....................................................................................... 8 2.3.2. IEEE 802.11 MAC LAYER: ............................................................................. 9

2.4. Hidden Terminal Problem ..................................................................................... 10

Chapter 3. Project Implementation ........................................................................... 11 3.1. SFU Wi-Fi .............................................................................................................. 11

3.1.1. Characteristics of SFU Wi-Fi ......................................................................... 11 3.2. Riverbed Modeler Implementation ........................................................................ 14 3.3. Performance Parameters: ..................................................................................... 15

Chapter 4. Simulation Scenarios and discussions ................................................. 16 4.1. Test scenario with one user and one AP .............................................................. 16 4.2. Ten users and One AP scenario ........................................................................... 17 4.3. Multiple access point and multiple users’ scenario ............................................... 18 4.4. Effect of device performance on delay .................................................................. 19 4.5. Moving Node scenario .......................................................................................... 20 4.6. Users with different load scenario ......................................................................... 22 4.7. Simultaneous requests scenario ........................................................................... 23 4.8. RTS and CTS effect .............................................................................................. 23

Chapter 5. Conclusion and Future Work ................................................................. 25 5.1. Conclusion ............................................................................................................ 25 5.2. Future Work .......................................................................................................... 26

References ..................................................................................................................... 27

vi

List of Tables

Table 1. Wi-Fi Characteristics ................................................................................. 6 Table 2. Specification of SFU Wi-Fi ....................................................................... 12

vii

List of Figures

Figure 1. Wireless LAN infrastructure ....................................................................... 4 Figure 2. WLAN examples ........................................................................................ 5 Figure 3. IEEE 802.11 2.4GHz Channels ................................................................. 7 Figure 4. Hidden Node Problem ............................................................................. 10 Figure 5. SFU WLAN Infrastructure ........................................................................ 11 Figure 6. AQ 3181 using Ekahau ............................................................................ 12 Figure 7. Signal Strength using Inssider ................................................................. 13 Figure 8. Signal strength using Wi-fi Inspector ....................................................... 13 Figure 9. Wi-Fi analysis in AQ 3181 ....................................................................... 14 Figure 10. Access point specifications ...................................................................... 16 Figure 11. Average Delay (sec) ................................................................................ 17 Figure 12. Average throughput (bits/sec) ................................................................. 17 Figure 13. Throughput and Delay in WLAN .............................................................. 18 Figure 14. Data dropped with 40 and 80 users ......................................................... 19 Figure 15. Delay comparison .................................................................................... 19 Figure 16. moving nodes scenario ............................................................................ 20 Figure 17. Throughput of mobile nodes .................................................................... 21 Figure 18. Delay(sec) in mobile nodes ..................................................................... 21 Figure 19. Delay with different loads ........................................................................ 22 Figure 20. Throughput in node0 and node1 ............................................................. 22 Figure 21. Delay Comparison in 20, 40 and, 60 devices .......................................... 23 Figure 22. Throughput in RTS .................................................................................. 24

viii

List of Acronyms

Wi-Fi Wireless Fidelity LAN Local Area Network MAC Media Access Control AP Access Point RTS Request to send CTS Clear to send IEEE Institute of Electrical and Electronics Engineers

1

Chapter 1. Introduction

Internet has become an integral part of our life. Over the past few years, there is

a significant increase in the popularity of mobile devices such as smartphones,

netbooks, notebooks and computer tablets, etc. This impact can be seen vividly

everywhere from personal use to the business purpose. Most companies use Internet

and smart devices to apply e- commerce, which includes advertising, selling, buying,

distributing products, and providing additional customer services. Individuals also use

the Internet for communication, entertainment, sharing information, purchasing goods,

and services, etc.

Wireless local area networks (LANs) have achieved a tremendous amount of

growth in recent years in the field of Internet. Among various wireless LAN technologies,

the IEEE 802.11b based wireless LAN technology, Wi-Fi, is the most prominent

technology today. Wireless Fidelity or "WiFi" has become the dominant wireless LAN

standard in the last few years.Wi-Fi stands for “Wireless Fidelity” which is one of the

popular wireless technologies and allows users to transfer and exchange data wirelessly

over the network, hence providing high speed internet connections. Wi-Fi is a system of

devices that use radio waves to communicate with each other, allowing for connection

between devices without the expense of wires or without needing them to be facing one

another.

In a university campus, many students and faculty members use several

personal wireless devices to connect to the school’s wireless network daily. With the

numerous simultaneous connections and multiple access points provided by the school,

a specific convention needs to be followed to determine the optimum network setup in

order to maintain the offering of a reliable wireless network.

In this project, the aim is to study the Wi-Fi performance of the SFU Burnaby

Campus. Slow wireless network have been always an issue at Simon Fraser University.

So, the scenario for the campus wireless network infrastructure is created in Riverbed

modeler to simulate a high- density environment. However, this wireless network

involves too many clients, would up to few thousands probably. The Riverbed Modeler

2

Academic edition is used for the simulation purpose which can simulate up to 80

clients. So, we will do the simulation with limited number of users. The high-density

lecture theaters (AQ 3181 and AQ 3182) are considered for the simulation. The various

possible causes to network slowness, blind or dead spots has been studied in the project

in order to find a solution.

3

Chapter 2. Wi-Fi Literature Review

2.1. Wi-Fi Technology overview

Different WI-FI standards were introduced throughout the last two decades. One

of the parts of Wi- Fi standards is 802.11, which is used to define an interface between a

wireless client and a base station.

The wireless infrastructure is shown in the figure below. It consists of a wireless

host which can be a laptop, tablet, smartphone, or desktop computer. The wireless host

can communicate with each other through Access point. It operates within a frequency

spectrum and it follows the IEEE

802.11 standard. It acts as a bridge between the wired and wireless devices. A

wireless host connects to another through a wireless communication link. Different

wireless link technologies have different transmission rates and can transmit over

different distances.

4

Figure 1. Wireless LAN infrastructure [12]

The host that is associated with that base station. The base station is connected to

the larger network for instance home network, or telephone network and act as a link-

layer relay between the wireless host and the rest of the world with which the host

communicates.

There are several specifications in the 802.11 standard as shown in the table 2.

The 802.11a,b,g,n,ac protocols are the popular ones, because these are used for

home/business wireless LAN networks. The 802.11 group currently operates in 5

different ISM Band frequency ranges: 2.4GHz, 3.6GHz, 4.9GHz, 5GHz, 5.9GHz bands.

Each channel in the bands are separated by about 5 MHz, and each channel has a width

of 16-22 MHz[8]. The 5 GHz band is preferred for modern standards as each channel

are non-overlapping[9].The channel band shape is also different depending on the

802.11 protocol used as different protocols use different modulation techniques[8].

5

Figure 2. WLAN examples [12]

802.11a: The 802.11a is an extension to 802.11 that provides up to 54 Mbps in the

5GHz band and has range up to 50m. 802.11a uses an orthogonal frequency division

multiplexing encoding scheme rather than FHSS or DSSS.

802.11b: 802.11b provides 11 Mbps transmission in the 2.4 GHz band and maximum

throughput of 6 Mbps. The 802.11b uses only DSSS. The 802.11g applies to wireless

LANs and has the maximum throughput of 25 Mbps. It provides 20+ Mbps in the 2.4

GHz band.

802.11g: This one is created around 2002/2003. 802.11g was designed with the intent to

get the best out of both 802.11a and 802.11b. Supports a bandwidth up to 54 Mbps like

802.11a, but uses the 2.4 Ghz unregulated band similar to 802.11b. 802.11g is also

backwards compatible with 802.11b, so 802.11b adapters will be able to receive 802.11g

signals. More costly than 802.11b.[2]

802.11n: 802.11n was designed to improve on 802.11g by adding Multiple-Input

Multiple- Output(MIMO) aka using multiple signal’s and antennae instead of only 1,

which allows for increased data throughput. Through better multiplexing and coding

schemes, the effective range is also much higher than its predecessors. [3] Accepted in

2009 by IEEE and capable of providing up to 300 Mbps, this was a huge improvement

over previous protocol. 802.11n is also backwards compatible with 802.11 b/g and can

use the 2.4 or 5 GHz frequency bands. [3]

6

802.11ac: 802.11ac is the further improvement of previous protocols specifically

802.11n by using dual band technology. It only operates in the 5 GHz band and deleiver

over 1.3Gbps using a 3 antennae setup. [3] 802.11ac wave 2 is an update to the

802.11ac protocol which uses Multi- User Multi-Input Multi-Output technology.

Table 1. Wi-Fi Characteristics Protocol Frequency Bandwidth MaximumData

Rate Maximum Outdoor Range

Modulation Power No. of Channel

802.11a 5GHz/3.7GHz 20 MHz 54Mbps 120m OFDM 40- 800mw

Up to 23

802.11b 2.4GHz 22 MHz 11Mbps 140m DSSS 100mw 3

802.11g 2.4GHz 20 MHz 54Mbps 140m OFDM/DS SS 100mw 3

802.11n 2.4GHz/5GHz 20MHz/40MHz 600Mbps(40MHz *4 MIMO)

250m OFDM 26

802.11ac 5GHz 20MHz/40MHz/80MHz/160

MHz

433Mbps per spatial

stream/1.3Gbps in a three-antenna

250m OFDM

802.11ad 60GHz 2.16GHz 7Gbps 100m OFDM

802.11ad: 802.11ad uses the 60 GHz band and has a bandwidth of over 2GHz instead

of using the 2.4 or 5 GHz band like the other protocols. It offers speeds of up to 7 Gbps,

which are much higher than previous standards but is relatively short ranged. 802.11ad

is also known as WiGig and officially accepted as a standard in 2012[6].

2.2. Wi-Fi Channels

There are several frequency bands within the radio spectrum that are used for the

Wi-Fi and within these there are many channels that have been designated with

numbers so they can be identified. The 802.11 make the use five distinct frequency

ranges: 2.4 GHz, 3.6 GHz, 4.9 GHz, 5 GHz, and 5.9 GHz bands. Each range is divided

into a multitude of channels. Different countries apply their own regulations to the

7

allowable channels, allowed users and maximum power levels within these frequency

ranges.

2.4 GHz : There is a total of fourteen channels defined for use by Wi-Fi 802.11 for the

2.4 GHz ISM band. Different number of channels are available in different countries. Out

of 14, 11 channels are allowed by the FCC that used in North American domain, and 13

channels are allowed in Europe where channels have been defined by ETSI. The WLAN

/ Wi-Fi channels are spaced 5 MHz apart (except for a 12 MHz spacing between the last

two channels)[9].

The 802.11 Wi-Fi standards have a bandwidth of 22 MHz and channels are on a

5 MHz. The 20 / 22 MHz bandwidth and channel separation of 5 MHz implies that

adjacent channels overlap and signals on adjacent channels will interfere with each

other. Due to the channel overlapping, there are maximum of three non-overlapping

channels which are 1,6 and, 11.

5 GHZ: 802.11 a, and n transmit in the 5 GHz U-NII bands. A total of twenty-five 20 MHz

channels in the 5 GHz bands can be utilized when designing a WLAN with a channel

reuse technique. As there are more channels available in the 5 GHz spectrum, so there is

less interference in this band in comparison to 2.4 GHz band and more room for

bonding. 802.11n technology introduced the capability of bonding together two 20 MHz

channels to create a larger 40 MHz channel in the 5 GHz spectrum.

Figure 3. IEEE 802.11 2.4GHz Channels[9]

2.3. WLAN overview

The wireless LAN can be implemented in two ways:

Infrastructure mode: In the infrastructure mode, the wireless network consists of at least

one AP (access point) connected to the wired infrastructure. All the wireless stations are

8

connected to the AP. An AP controls encryption on the network and can route the

wireless traffic to a wired network.

Ad-Hoc Mode: Access point is not required in Ad-Hoc mode. The wireless station is

connecting to each other directly without using an AP or any other connection. This

topology is very useful to set up a wireless network quickly and easily. Ad-Hoc mode is

also called peer to peer mode or (IBSS) Independent Basic Service Set.

2.3.1. Wi-Fi Radio topology

There are two layers in the Wi-Fi, the Physical (PHY) and the Media Access

Control (MAC). The physical layer refers to the three technologies supported by the

standard. They are:

Frequency Hopping Spread Spectrum (FH):

It uses a narrowband carrier that changes frequencies at a predetermined rate

which is known to both the transmitter and receiver. Each access point creates its own

LAN segment which can transmit multiple transmissions. In dense user environments,

many access points can relate to overlapping coverage, enabling load balancing. Load

balancing enables the clients to choose the access point that increase the

performance[12].

Direct Sequence Spread Spectrum (DS):

It spreads the signals over a wider bandwidth than FH systems. It generates a

redundant chip for each signal burst sent. The longer chipping codes require more

bandwidth than FH transmissions. So, it supports few channels, and therefore fewer

users. DS is more secure and provide data rates 1, 2, 5.5, 11 Mbps[12].

Infrared (IR):

It makes the use of extremely high frequencies which are just below visible light

in the electromagnetic spectrum. Infrared is currently capable of higher data rates than

RF. It requires directed line of sight or reflective capabilities for transmission. Infrared

signal used here doesn’t penetrate walls, so the signal are kept inside the room. Thus,

makes less interference with the objects and prevents eavesdropping.

9

2.3.2. IEEE 802.11 MAC LAYER:

MAC stands for "Medium Access Control". Its main function is to control access

to a shared medium. The air interface is a shared medium through which all multiple Wi-Fi

stations and access point (AP) attempt to transfer data. MAC layer function is to

implement the control mechanisms which allow the multiple devices to communicate by

sharing the same medium as specified in the standard[11].MAC layer functions include:

Accessing the medium : The 802.11 standard uses an access method called

Distributed Coordination Function (DCF) which specifies the use of Carrier Sense

Multiple Access with Collision Avoidance (CSMA/CA) algorithm as the media access

scheme.

Association: It means to establish the wireless links between clients and AP in the

network. The station first scans the air to check the access points from beacons sent by

the access points. Then the association process starts.

Reassociation: This is performed when there is a handoff of clients as they roam in the

network.

Authentication: The 802.11 Standard has two ways of addressing authentication. By

default, the standard is an open system, allowing any client with a wireless connection

device to address the network without authentication. Another standard provides a more

secure network. In this, a shared key is configured into the AP and its wireless clients.

Only those with the proper key will be allowed to access the AP.

When a wireless device is linked with an Access point, it can start sending and

receiving data to and from the access point. A multiple access protocol is needed to

coordinate the transmissions between them. Because many wireless devices and AP

itself are using the same channel for the transmission. To solve this problem, it makes

the use of Carrier Sense Multiple Access with Collision Avoidance Protocol (CSMA/CA).

If channel is busy, the wireless device waits till it's free and this duration is Distributed

Inter-frame Space (DIFS) duration[11]. After that it waits for a random interval of time

before transmitting the data packets. This time period reduces the chances of two

waiting devices end up transmitting at the same time. Network Allocation Vector is used

for collision avoidance in CSMA/CA.

10

2.4. Hidden Terminal Problem

The hidden node problem arises when a transmitting wireless station does not

know about the existence of another station while transmitting data to a third station

which is in range of both the wireless stations. In this case, the normal collision

avoidance is not effective, and the data packets will often collide at the third station.

Figure 4. Hidden Node Problem[12]

Request-to-Send and Clear-to-Send are used to solve the hidden-node problem.

The sender station sends an RTS (Request To Send) frame to the target node. If the

channel is clear, the target node sends a CTS (Clear To Send) frame to inform the

sender that it may transmit the data packets. It also tells other stations to refrain from

using the channel for the specified amount of time[11].

11

Chapter 3. Project Implementation

3.1. SFU Wi-Fi

The SFU Wi-Fi structure is shown in the figure. The connection path of a data

packet to the outside world is generally as following: A mobile device is connected to the

Access Point and this known as the Access layer. Edge Switch (Juniper) and core routers

(Juniper) are the router for the different buildings. The switches and core routers linking

with edge switch form the second layer which is distribution layer. The BCNET is the

internet service provider for the SFU network.

Figure 5. SFU WLAN Infrastructure

The core layer is the highest layer which contains wireless controller and core routers

that lead to the outside world.

3.1.1. Characteristics of SFU Wi-Fi

In SFU Burnaby Campus, all APs are connected to the wired infrastructure via 1

GbE uplinks. The number of users associated with an AP varies with time and location. At

some locations, it may be 40-50 clients on an AP which is split between the 2 radios on

each AP. The other specifications are:

12

2.4Ggz: 802.11b is disabled, 802.11g/n enabled, minimum basic rate set to 12Mbps

5Ghz: 802.11a in enabled, 802.11n enabled, 802.11ac (wave 1) is enabled in other

locations but not Library/ASB, minimum basic rate of 12Mbps.

Table 2. Specification of SFU Wi-Fi Base Rate 62 Mbps

Channel width 20 MHz

Max Throughput 300 Mbps

Beacon 100 ms

12 dbm transmitted Power 15mW

It is observed that in room AQ 3181 which is a big lecture theatre has four APs.

The heat map view using Ekahau is shown in the figure above. The distance of the

workstation from the Access point matters in real life. The signal strength decreases with

the increase in distance from the Wi- Fi.

Figure 6. AQ 3181 using Ekahau

13

Figure 7. Signal Strength using Inssider

The effect of signal strength is explained in the figure given below. It drops as the

work station is moving away from the access point range. The points in the graphs

where the value reaches to - 90 dm are the locations where the signal is weak and there

is no reception signal from AP.

Normally, the dbms values of the various APs are in range of 50 to 70 dBs and

frequency is either 2.4 MHZ or 5MHZ.

Figure 8. Signal strength using Wi-fi Inspector

14

Figure 9. Wi-Fi analysis in AQ 3181

3.2. Riverbed Modeler Implementation

The simulation tool used here is Academic edition of Riverbed Modeler 17.5

which is a set of decision support tools, providing a comprehensive development

environment for specification, simulation and performance analysis of communication

networks, computer systems and applications. It allows us to create models in great,

execute simulations, and analyze the output data. It has the tools for all phases including

model design and simulation, study and analysis of the data, etc. The basic building block

is a node, which is an underlying model. Nodes are corresponding to communication

devices such as PC, file server, printer, and router.

In this project, the Wi-Fi networking model is created which resembles the

network specification of the campus Wi-Fi. The Access Point (AP) are added as a

wireless router to transmit wireless signals, and various numbers of workstations

according to different scenarios. The AP is connected to a switch and then connected to a

server which provides applications used for the workstations. The applications and

profiles are defined by adding a node for each. The wireless stations are associated with

the profiles in order to use the applications.

15

3.3. Performance Parameters:

Throughput: Throughput is an important factor to evaluate the QoS in Wi-Fi. It is the

rate at which the data is successfully delivered over a communication channel. In other

words, throughput is the rate of successful packet delivery. The throughput is calculated

by number of bytes received and then multiplying by 8 to convert from bytes to bits,

dividing by 1000000 which achieve Mbits, after that dividing by current time which gets

Mbits/sec.

Packet Loss Rate: Packet Loss Rate occurs when the data from one node fails to reach

the destination node and is calculated by storing the number of packets lost which is

then divided by the current time to achieve packets lost per second.

End-to-end Delay: Another important parameter is end-to-end delay which is the time

taken by a packet to travel from source to destination in a network.

16

Chapter 4. Simulation Scenarios and discussions

4.1. Test scenario with one user and one AP

A test scenario is created to check the Wi-Fi network. A single node with single

access point is present and using the applications like file transfer, emailing and, light

browsing. The simulation time is set to one hour. The results of delay and throughput are

shown in the figures below. The Access point Specifications for all the scenarios are

same as the SFU Wi-Fi which is given in the figure below:

Figure 10. Access point specifications

17

4.2. Ten users and One AP scenario

To study the delay and throughput effect on the number of users, a scenario with

ten users and one access point is created. It is observed that the average delay is

increased to 1.6 from 0.8 and the throughput rises to 800,000 bits/sec. For the first ten

minutes, the delay increases continuously as all the nodes have data packets to send

and after reaching 20 minutes into the simulation its value ranging between 0.0014 to

0.0016 secs.

Figure 11. Average Delay (sec)

Figure 12. Average throughput (bits/sec)

18

4.3. Multiple access point and multiple users’ scenario

In this section, the AQ 3181 Wi-Fi network is implemented. There are four access

points in this room, and it has the capacity up to 200+ people. But in Riverbed modeler

Academic edition we can simulate 80 nodes. The delay and throughput effect is

observed with 1, 10 ,40 and, 80 users which are associated with 4 access points. The

stations are using FTP, email, and heavy browsing. The simulation period is 1 hour.

The delay values are very large in case of 80 users and it is roughly double of 40

users which is 0.16 in case eighty users and 0.07 in forty users. It is because of the

simultaneous requests as all the nodes are trying to transmit data together and it effect

the throughput of all the workstations.

The delay performance can be improved if the number of work station decreases.

It will decrease the load to the access point, hence improves the delay.

Figure 13. Throughput and Delay in WLAN

The Data dropped ratio also increases with the number of work station. The

value is worst in case of 80 users as it reaches to 120,000 bits/sec as shown in the

graph.

19

Figure 14. Data dropped with 40 and 80 users

4.4. Effect of device performance on delay

Figure 15. Delay comparison

The effect of the device performance on delay is observed. In this scenario, the

delay is observed for 20 30 and 40 devices. The delay is less when we have 20 devices

and it became double when the devices reaches 40. However, when we have 30 devices

and one device with poor performance, it leads to a huge increase in delay value which is

more than 40 devices.

While observing the delay with 30 devices, one device is added to the network

which has low signal reception , due to the old technology and its Wi-Fi speeds may be

20

slower than others. This device may also be impacting the performance of the whole Wi-

Fi network. All Wi-Fi devices have to communicate with the access point, the legacy

devices communicates slowly with the AP and every other device will have to wait longer

until this device finishes thus slowing the experience on the other devices. Therefore, a

large spike is seen in the delay in case of 30 devices with one device with low

performance.

4.5. Moving Node scenario

Figure 16. moving nodes scenario

In this case, the two nodes are moving , the node 0 is associated to Ap1 and the

node 1 relates to Ap 2. Initially both the nodes are away from the access points. The

throughput graph describes the effect of distance from the Ap.

Before just entering the AP range, the workstation have a lot of data need to be

send by using FTP, but due to the signal strength, it cannot be done as required time.

Once the station move into the area B which is inside the affective range of AP,

workstation send all the data in the buffer which supposed to be send in the earlier time.

That’s why we saw a very sharp pulse at the beginning. Then everything back to

schedule throughput back to normal. At last when the work stations move out the range,

throughput fade out.

21

Figure 17. Throughput of mobile nodes

The delay in the case of moving nodes varies as it is entering the range of the

access point. When it’s in the coverage area the value starts to decrease gradually as

shown in the figure below.

Figure 18. Delay(sec) in mobile nodes

22

4.6. Users with different load scenario

In this section, we are using two work station where one is using applications

with light load and other is using heavy load(heavy browsing and file transfer). Both are

in the range of the same Access point. The simulation time is one hour. The increase of

load on 1 workstation of the networks will decrease another workstations throughput

bandwidth.

Figure 19. Delay with different loads

For the heavy load file transfer workstation, it cannot complete the first

application request before the upcoming request. So, the throughput cannot take a break

and must increase the throughput bandwidth to finish the job.

Figure 20. Throughput in node0 and node1

23

4.7. Simultaneous requests scenario

Figure 21. Delay Comparison in 20, 40 and, 60 devices

This scenario is created to observe the effect of simultaneous requests on the

network. When students are entering in the classroom at the same time, they are trying

to connect to the access point at the same time. As many of the devices are

communicating with the AP, it results into delay. It increases as the number of devices or

the simultaneous requests increases in the network.

4.8. RTS and CTS effect

As the number of workstations and the size of packets increase, the performance

will be reduced. In this section, the improvement in performance is observed by first

applying RTS (Request-to Send) threshold. Number of APs are set to and 10

workstations. The Applications used are Email, FTP, and Web Browsing.

The request-to-send mechanism is a handshaking procedure used by the IEEE

802.11 wireless network to reduce the possibility of collision. RTS threshold specifies a

threshold to determine whether RTS frames is required for a data frame.

As the number of workstations in the network increases, the wireless LAN

throughput will reduce. This problem can be solved by applying the RTS. The default

value for wireless LAN parameter RTS of the AP is none, change the RTS Threshold to

1024 bytes.

24

Figure 22. Throughput in RTS

It is a four-way handshaking technique instead of the basic two-way handshaking

technique for packet transmission. RTS frames are waiting to receive CTS (Clear-to-

Send) frame, it will take a certain period while data are waiting in the transmission buffer.

On the other side without using RTS, data are sent immediately once it is ready to send.

25

Chapter 5. Conclusion and Future Work

5.1. Conclusion

In this project, different scenarios has been created to analyze the reason of slow

Wi-Fi problem in SFU. By using the access point specifications of the real environment,

the effect of number of users, access points, user load, device performance,

simultaneous requests, etc. has been observed. The real time traffic data for the users

has been obtained by using the Wireshark. The applications used by the devices are

designed that run on top of TCP followed by UDP.

It is observed that with increase in the number of users on the same Access point

results in increase in delay and the average throughput decreases. It can be improved

by adding more access points to the network. When the devices are moving away from

the wireless coverage area, it leads to a huge increase in delay. Also, the device

throughput decreases when the device is moving away from the AP.

The decrease in the signal strength of Wi-Fi also depend on the device we are

using for communication. If we are using a legacy device which is operating on the old

technology, then it will take more time to communicate with the wireless access point.

This will result in long waiting time for all the other devices which are communicating

with the router.

When the students are entering the lecture theatre at the same time, they are

trying to connect to the router at the same time. That means they are trying to send data

simultaneously and it will decrease the average throughput. More the simultaneous

requests, more will be the delay in completing the requests.

The two users trying to send different loads are also compared. When the client

is dealing with heavy load(heavy web browsing, heavy file transfer, etc.), it needs more

bandwidth. As a result, it will decrease another client’s throughput bandwidth.

The effect of using RTS and CTS in the wireless network is also observed.

Request to send in the network helps to reduce the possibility of the data packet collision.

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In a large network where nodes are sending large size of data packets, it is advised to

use RTS. It will reduce the packet collisions and retransmission of the packets which

results in overall increase in the throughput.

Also, to avoid the problems of the co-channel interference, the access points

using the same channels should be placed far from each other and their power should

be optimized in such a way that there is no leakage of the power to the neighbour AP.

The coverage of the Access points can be increased by using the high gain antennas but

that would be in-breech of the Wi-Fi standards.

5.2. Future Work

In the Riverbed Modeler Academic edition, the nodes are limited to a fixed

number(80). So, the simulation scenarios used in the project are limited to 80 clients

while in the real world, more students are present in the classrooms. Also, the academic

edition does not include the support walls or other physical interference which will

responsible for Wi-Fi signal degradation. In future, all these should be taken into

consideration to produce more realistic scenarios.

Another tool which can be used is NS3. It is a network simulator tool and it

makes the use of Network Animator or NAM which would help to visualize the

transmission of packets in a much different way. It demonstrates the individual packets

being sent, dropped, received in real-time, versus a graph of statistics. Also, NS3 can

model 2 dimensional walls (infinite 3D height) which will provide the results closer to the

real world.

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References

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[7] Radio-electronics.com, 'IEEE 802.11ad | Microwave Wi-Fi, WiGig | Tutorial', 2015. [Online]. Available: http://www.radio-electronics.com/info/wireless/wi-fi/ieee-802-11ad- microwave.php. [Accessed: 19- Jun- 2015].

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