zohaib 3rd seminar report

8/3/2019 Zohaib 3rd Seminar Report

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SHIATS-Deemed to be University Allahabad

1Throughput and Delay Performance of Multi-Channel Multi-RadioWireless Ad hoc Network under IEEE802.11n

CHAPTER 1

INTRODUCTION


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Chapter 1

1. INTRODUCTION

Over the past decade, IEEE 802.11 technologies have been broadly applied to wireless local

area networks (WLANs) deployments. Since the IEEE 802.11 standard was specified, products

based on this standard have had a significant growth in sales all over the world. The IEEE

802.11 standard has allowed a better inter-operability among products from different vendors,

and also led to a large reduction on cost of these products. Therefore, many organizations are

taking advantage of WLAN benefits such as:

1. Mobility, that allows user to be truly mobile as long as the terminal is under the networkcoverage area.

2. Ease of use, because the WLAN is transparent to the users network operating system sinceapplications work in the same way as they do in wired LANs.

3. Installation simplicity and flexibility, since wireless LANs enable networks to be set upwhere wires might be impossible to install, and

4. Cost, which is on average lower than the cost of installing and maintaining a traditionalwired LAN, for two reasons. First, WLAN eliminates the direct costs of cabling and the

labor associated with installing and repairing it. Second, because WLANs simplify moving,additions, and changes, the indirect costs of user downtime and administrative overhead are

reduced.

For all the mentioned reasons and others, the dominant standard for WLANs is IEEE

802.11, which provides specifications for both the physical layer and the medium access

control (MAC) layer. The physical layer is the interface between the MAC and the wireless

media where data is transmitted and received,while the MAC layer provides functionality to

allow reliable data delivery for the upper layers over the wireless physical media.

By definition, a WLAN usually covers a small area, typically less than 500 meters in

diameter. To set up wireless ad hoc network with inexpensive, commercial off -the-shelf

(COTS) devices, the concept of wireless mesh network (WMN) has been proposed and is

considered as a cost-effective solution.


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Fig 1.1: Mesh router & mesh clients.

Mesh networks can be seen as one type of mobile ad hoc network (MANET), but the

later has to deal with problems introduced by the mobility of the nodes and the lack of

infrastructure. WMN differs from other networks in that the components can all connect to

each other via multiple hops, and the backbone nodes generally are not mobile, or support little

mobility.

In a WMN, nodes can automatically establish an ad hoc network and maintain the

connectivity; therefore the network is dynamically self-organized and self-configured.

According to I.F. Akyildiz et al [2005] there are two types of nodes in WMN: mesh routers

and mesh clients Figure1.1. Mesh routers are typically equipped with multiple radio interfaces

in order to provide a backbone for routing packets. Mesh clients, on the other hand, incorporate

network interface cards that connect them to the WMN through mesh routers. An example of

WMN is illustrated in Figure1.2, where mesh routers are set up on top of big buildings and


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mesh clients are deployed at the rooftop of residential houses.

Figure 1.2: An example of wireless mesh networks.

Moreover, real examples of operative WMN can be found in many cities throughout the United

States such as Los Angeles, Miami, and many others in which the so-called Municipal wireless

networks have been deployed.

Table 1. Status of Municipal Wireless Networks in USA until January, 2007.

As January, 2007, more than 190 cities in the United State have already deployed Municipal

Wireless Network as shown in Table 1 Also, many cities are requesting proposals from vendors

to conduct feasibility studies for implementing these networks, and others are already in

progress of deployment. Thus, the investment on Municipal Wi-Fi reached $235 million at the


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end of 2006 and doubled by 2007.

Many government agencies are interested in deploying IEEE 802.11 wireless networks

because of public and administrative advantages; moreover, they consider that municipal Wi-Fi

is a vital solution to last-mile broadband problems in many locations which are too far from

physical facilities of providers, or the costs for implementation are too high. Since the

deployment of wireless networks is relatively inexpensive and they can offer broadband

capabilities to businesses, residents, and tourists, they become important economy engines in

many scenarios.

Currently, there are already many applications for Municipal wireless networks which

can be categorized into two types 1) Municipal-related applications, and 2) Public access

applications. According to Muni wireless. Municipal wireless networks [2007] Survey

report, 80% of municipal networks utilize the first type of applications such as public safety,

building inspections, public works, supervisory control and data acquisition (SCADA) systems,

and parking meter and traffic management. And about 50% of the existing or deployed

networks are used to provide free public access to residents and visitors, and another 50% offer

paid public access to residents and visitors. Table 2 shows other most used applications in IEEE

802.11 municipal Wi-Fi.

Table 2: Deployed Municipal Wi-F i applications in 2007.

1.1 OBJECTIVE

Our objective is to investigate the performance of IEEE 802.11n in MCMR wireless ad hoc

networks. Particularly, we will focus on packet aggregation, which is the main feature of IEEE

802.11n compared to previous media access control (MAC) schemes.


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CHAPTER 2

REVIEW OF LITERATURE


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CHAPTER 2

2.1 REVIEW OF LITERATURE

I.F.Akyildiz et. al [2005] have discussed about Wireless mesh networks (WMNs) which

have emerged as a key technology for next-generation wireless networking. In order to

provide a better understanding of the research challenges of WMNs, this article presents a

detailed investigation of current state-of-the-art protocols and algorithms for WMNs. Open

research issues in all protocol layers are also discussed, with an objective to spark new

research interests in this field.

Kejie Lu et.al [2007] have discussed about Ultrawideband (UWB) communication that it is

an emerging technology that promises to provide high data rate communication for wireless

personal area networks. One of the critical challenges in UWB system design is the timing

acquisition problem, i.e., a receiver needs a relative long time to synchronize with transmitted

signals. Clearly, the timing acquisition overhead will significantly limit the throughput of high

data rate UWB ad hocnetworks.

A. Raniwala e t . a l [ 2005] ha ve p ro po s ed t h a t Even though multiple non-overlapped

channels exist in the 2.4GHz and 5GHz spectrum, most IEEE 802.11-based multi-hop ad hoc

networks today use only a single channel. As a result, these networks rarely can fully exploit

the aggregate bandwidth available in the radio spectrum provisioned by the standards. This

prevents them from being used as an ISP's wireless last-mile access network or as a wireless

enterprise backbone network.

S. Merlin et.al[2007] have discussed about a joint congestion control, channel allocation and

scheduling algorithm for multi-channel multi-interface multihop wireless networks is

discussed. The goal of maximizing a utility function of the injected traffic, while guaranteeing

queues stability, is defined as an optimization problem where the input traffic intensity,


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channel loads, interface to channel binding and transmission schedules are jointly optimized

by a dynamic algorithm.

A. K. Das et.al [2005] have discussed about the combination of multiple radio nodes in

conjunction with a suitably structured multi-hop or mesh architecture has the potential to solve

some of the key limitations of present day wireless access networks that are based on single-

radio nodes. This paper addresses the channel assignment problem for multi-channel multi-

interface (radio) wireless mesh networks.

Almeroth K.C. et.al [2006] have discussed about the capacity problem in wireless mesh

networks can be alleviated by equipping the mesh routers with multiple radios tuned to non

overlapping channels. However, channel assignment presents a challenge because co-located

wireless networks are likely to be tuned to the same channels. The resulting increase in

interference can adversely affect performance. This paper presents an interference-aware

channel assignment algorithm and protocol for multi-radio wireless mesh networks that

address this interference problem.


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CHAPTER3

MATERIAL AND METHOD


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CHAPTER 3

3.1 THE IEEE 802.11

In this section we present the basics of the IEEE 802.11 standard that we are going to use in the

rest of this thesis. Many concepts and definitions are needed in order to better understand and

propose enhancements to the IEEE 802.11 standard.

3.1.1 IEEE 802.11 Architectures

The IEEE 802.11 architecture comprises several components and services that interact to

provide wireless communication to stations which are any devices that incorporates the

functionality of the IEEE 802.11 protocol and can connect to the wireless media.

The IEEE 802.11 standard specifies three primary setups. The first setup is a Basic

Service Set (BSS), which is defined as a group of stations that communicates with each other in

a geographical area known as Basic Service Area (BSA). When these stations can communicate

without the aid of an infrastructure network, they are referred to as an Independent Basic

Service Set (IBSS) which is the formal name of an ad hoc network in the IEEE 802.11

standard. These stations operate in the ad-hoc mode because they communicate directly with

another station in its transmission range.

In comparison, in the infrastructure mode, a station in a BSS communicates with

another through a Base Station (BS) which is also called Access Point (AP) if it is connected

to a wired network. The BSS operating with a BS is known as the Infrastructure Basic Service.

In addition, another setup known as Extended Service Set (ESS) can be formed. In thissetup, BSs (or APs) provide the integration points for network connectivity among different

BSSs. Therefore, a network backbone, also known as distribution system (DS), is formed. The

DS is responsible for MAC level transport of MAC data units, and is implementation

independent meaning that the DS could be a wired Local area network (LAN), Metropolitan


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area network (MAN), or another IEEE 802.11 wireless medium.

In the infrastructure mode, a station needs to join a BSS to communicate. It obtains

synchronization information from periodic beacons from the BS. It can either obtain this

information by requesting it from the BS (active probing), or it can wait for the periodic

beacon from the BS. Before being able to send and receive data, the station has to go through

an authentication and association process. The IEEE 802.11 standard not only defines a

Medium Access Control (MAC), but also the related management protocols and services, and

the physical layer. Also, important timing intervals are specified by the standard.

Short Inter-frame space (SIFS). It is the shortest time interval. It is used between

a frame and its acknowledgment. It is long enough for the sender to switch to the

receiver mode.

Slot time (Slot). A little longer than SIFS, it is the basic time unit for the binary

exponential back-off algorithm spelled out in the standard. PCF inter-frame space (PIFS). It is equal to the SIFS plus one Slot. It is used by

the Point Coordinator to get higher priority in accessing the medium.

Distributed inter-frame space (DIFS). It is equal to the SIFS plus two Slots. It is

used before starting a new transmission.

3.2 The Distributed Coordination Function (DCF)The IEEE 802.11 MAC layer offers two types of service, the Distributed Coordination

Function (DCF), and the Point Coordination Function (PCF). The DCF protocol allows stations

to access the medium in a distributed manner. There is no central entity controlling the use of

the shared channel. The DCF defines two access mechanisms: The Basic Access and the

RTS/CTS.

3.2.1 Basic Access Mechanism

The Basic Access scheme is carrier sense multiple access with collision avoidance

(CSMA/CA). When the MAC needs to transmit a frame, it physically senses the medium to

check its status. If the medium is free, the station waits for an interval of DIFS to check that the

medium remains free. If it is still free, the station sends its frame. Otherwise, the MAC selects a


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back-o value randomly from a contention window. Figure 2.1 shows this scheme. If a collision

happens, the contention window is set to twice its size and a back-o value is chosen from the

new interval. After a successful transmission, the contention window is reset to a pre-set

minimum value. The random back-o is also called after each successful transmission and each

retransmission to reduce probability of collisions. The IEEE 802.11 MAC uses a positive

acknowledgment scheme to detect collisions. Each unicast frame sent by the MAC has to be

acknowledgment by the receiver; otherwise the frame is retransmitted by the MAC layer.

Broadcast packets are not acknowledged. Also, retransmissions are limited to a maximum

number of tries, after which a packet is dropped.

Figure 3.1: IEEE 802.11 DCF Basic Access Mechanisms.

3.2.2 The RTS/CTS Mechanism

In a wireless network, the sender node cannot detect a collision because it occurs at the receiver

side. When a packet collides at the receiver, the whole packet still needs to be transmitted and

then retransmitted if an acknowledgment packet is not received. In addition, stations in the

receivers surrounding may not sense a transmission from the sender. If any of these stations

transmits, there will be a collision at the receiver. This is referred to as the Hidden Terminal

problem. To overcome this issue and enable faster collision detection, the MAC specifies a

prior hand-shake. Whenever a station has data to send, it first sends a Request to Send (RTS)

frame. The destination replies with a Clear to Send (CTS) frame. These two frames contain

information about the duration of the next data frames. All neighbor stations hearing these

frames set a variable called Network Allocation Vector (NAV) to keep track of the availability


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of the medium. Checking the NAV before a trans-mission is also called a Virtual Carrier Sense

mechanism This protocol is depicted in Figure 3.2. The attribute dot11RTSThreshold in the

management information base (MIB) specifies the minimum size of the frame requiring a

RTS/CTS exchange.

Figure3.2:IEEE802.11DCF RTS/CTS Access mechanism.

3.3 IEEE 802.11 BASED WIRELESS MESH NETWORKS

The IEEE 802.11 is one of the most implemented standards when a deployment of wireless

local area networks is required. The current role of IEEE 802.11 is limited to mobile client to

AP communication. Currently, there is a big interest in expanding IEEE 802.11 networks to

large-scale enterprise scenarios to provide wide-area wideband access to a significant number

of users. This requires a proliferation of interconnected APs over the desired coverage area to

form a wireless mesh network as shown in Figure 3.3.

As a first step to support these deployments, the IEEE 802.11 has two additional modes

of operation: the ad hoc mode and the wireless distribution system (WDS) mode. In the ad hoc

mode a single-hop ad hoc network is formed. Here nodes communicate with each other directly


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without an AP. The WDS enables point-to-point AP relay links where each AP is not only a

base station, but also a wireless relay node.

Fig 3.3: IEEE802.11 based wireless mesh network

Traditional multi-hop wireless networks have almost exclusively comprised of single-

radio nodes. For various reasons, like the channel assignment problem for a single-radio mesh,

such networks cannot electively scale to take full advantage of the increasing available system

bandwidth. Therefore, the use of multiple radio nodes in a wireless mesh network appears to

provide one of the most promising avenues to network scaling. Multiple radios significantly

increase the potential for better channel selection and assignment techniques, and route

formation while the mesh allows improved interference management and topology control.

3.3.1 Multi-Channel Single-Radio (MCSR) Mesh Networks

Typically, wireless mesh networks make use of a single radio interface to communicate with

neighboring nodes. In a multi-hop environment, one approach is that all single-radio nodes use

the same channel to avoid the need for channel switching, even if multiple channels are

available. Clearly, single radio wireless devices have a limitation which is that they operate in

half-duplex mode, meaning that they cannot receive and transmit at the same time. However, a


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radio interface can be switched among different channels. Such interface switching technique is

often used to improve the channel utilization. In order to maximize the number of simultaneous

transmissions in the network, it should be possible to utilize all the available non interfering

channels.

Using multiple channels requires channel scanning, selection, and switching a radio

such that two adjacent nodes share a common channel. However, the inconvenient in a multi-

hop single-radio environment is that the frequently switching increments the end-to-end delay

as the number of available channels increases, as well as the number of nodes along the path.

3.3.2 Multi-Radio Wireless Mesh Networks

For all the reasons mentioned in the previous subsection, multi-radio mesh networks are

expected to be a key component in achieving both network scalability and adaptability in future

wireless networks, because they introduce several new degrees of freedom that overcome the

key limitations of single-radio wireless devices.

Fig3.4:Five-node Multi-Radio Wireless Mesh Network.


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Multiple radio nodes are effectively full duplex, meaning that one node can receive on channel

1 on one interface while simultaneously transmitting on channel 2 on another interface, thereby

doubling the node throughput, at least in theory.

In Figures 3.4 and 3.5, we show examples to motivate the improvement in throughputthat can be obtained with multiple radios and/or multiple channels. In Figure 3.5, with one

radio at node 2, each of the two flows, 1 2 3 and 4 2 5, receive an end-to-end

throughput of S/2 bps (where S is the source rate) if they are scheduled at different times.

However, if the two flows are simultaneous, the receive rate for both flows drops to S/4 bps.

With two radios and availability of two orthogonal channels, the receive rate for both flows

increases to S/2 bps, the same as each flow would have received if they were scheduled at

different times.

Figure 3.5 illustrates a scenario when having multiple orthogonal channels is helpful

even with one radio. For example, if two channels are available, then both of them can be used

for the two transmissions at the same time. The receive throughput for each flow in this case is

S/2 bps.

Fig3.5:Three-node Multi-Radio Wireless Mesh Network.

3.3.3 Channel Assignment

In this subsection we show various channel assignment approaches. Basically, the main issue

here is which radio a node should use to transmit to a particular neighbor and when to bind the

radio to a particular channel.


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The first approach is a simple one which is using a static binding channels to interfaces.

When the system initializes, each interface is assigned to a channel. Occasionally, this

assignment could change over time and the change should be slow of relatively compared to

packet transmission duration. Note that in the static binding approach, no change to the IEEE

802.11 standard is required unlike other more complex schemes that require some level of

coordination among nodes, involving a modification of the MAC protocol.

In MCMR networks, when two nodes can communicate over more than one interface, it

is not a trivial issue to answer which radio to use when nodes have more than one channel in

common. Then, it is possible to use the available interfaces in a round- robin manner or use the

stripping approach which consists in using the available interfaces in a packet-by-packet

base. However, packets can arrive out of order to the receiver which would require more

processing time leading to a low throughput in higher layers.

The Multi-radio Unification Protocol (MUP) which unifies multiple interfaces into a single

logical one as seen by the higher layer. This approach outperforms the previous because it

maintains a high throughput when packet reordering is needed at the receiver. This link layer

protocol named MUP coordinates multiple IEEE 802.11 radios operating in multiple channels

to exploit the available spectrum as efficiently as possible and achieve the highest throughput.

Nevertheless, MUP is not about assigning channels optimally, but using pre-assigned channels

efficiently in a multi-hop network.

Furthermore, there are other approaches that consider a hybrid manner of assigning

channels. For example, in one approach, one channel is assigned to a fixed interface in every

node as its desired channel for reception, and this is communicated to neighbor nodes by a

higher layer protocol. The other interfaces can dynamically switch to other channels, therefore

when a sender wants to send a packet; it switches one of its dynamic interfaces to the receivers

fixed channel and transmits the packet.

A variation of the previous approach is that all nodes share a common control channel,

and assign their fixed interface to this channel. The control channel is used to determine which

channel to use for the data transmission. However, the disadvantage of these approaches is that

the control channel becomes a bottleneck as the network scales. Further, if the data packets are


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short, then the control channel becomes inefficient for the overall network.

3.4 THE IEEE 802.11n

IEEE 802.11n is a proposed amendment to the IEEE 802.11 wireless networking standard to

improve network throughput over previous standards, such as IEEE 802.11a, and IEEE 802.11b

and IEEE 802.11g by adding multiple-input multiple-output (MIMO) and 40 MHz operation to

the physical (PHY) layer . The estimated throughput of IEEE 802.11n is expected to reach to

more than 500Mbps.

In this purpose, the following characteristics are considered:

1. Pre-coding and post-coding techniques. Pre-coding includes spatial beam forming toimprove the received signal quality, and spatial coding to increase data throughput by using

spatial multiplexing, and to increase range by exploiting spatial diversity.

2. Aggregation of MAC service data units (MSDUs) and aggregation of MAC protocol dataunits (MSPUs).

3. Backward compatibility. Ensure that new devices can work with legacy devices. Lastyear, the Draft 3.02 was approved and the final publication is expected to be ratified in July

2009. Currently, manufacturers are now releasing pre- N, draft n or MIMO-based

products based on early specs.

3.4.1 Multiple Input - Multiple Output (MIMO)

Currently, research on the WMNs mainly focuses on the media access control (MAC) protocol

and network layer, although the physical layer plays also an important role in the performance

of the WMNs. In the literature, we can find many physical layer techniques. One of the most

important techniques is the use of multiple antennas. It is possible to improve the WMN

capacity and throughput, and the routing performance by using multiple antenna techniques. Inaddition, other benefits can be achieved such as increased energy efficiency, better quality of

service (QoS), and improved location management.

Multiple antennas have been implemented in the BS side in recent years. This has lead

to the use of smart antennas to achieve high-rate multimedia transmissions over wireless


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channels, and overcome the limited channel bandwidth. Moreover, with the advances in

hardware, multiple antennas could also be implemented in the mobile station (MS) side. Thus,

the new technique of MIMO has arisen. In MIMO, channels are built between the transmitter

and the receivers as shown in Figure 3.7. MIMO systems can be seen as an extension of smart

antennas techniques. When multiple antennas are implemented in the mobile station side so

they form a MIMO link, the optimization of the transmitter and receiver antennas can be

maintained in a larger space, and also allows multipath propagation which improves the system

capacity. . In this way, the data rate could be increased. With MIMO, two pairs of nodes

located in each others radio vicinity may potentially communicate simultaneously, depending

on the directions of transmission.

Figure 3.6: Multiple Input Multiple Output (MIMO).

We can find two types of gains when using MIMO systems: diversity gain and spatial

multiplexing gain. Diversity gain reduces fading, by sending and receiving signals that carry

the same information through different paths, this is known as transmit and receive diversity. In

this way, the receiver can obtain independent replicas of the same data and thus reception could

be more reliable. Spatial multiplexing is the transmission of independent information streams in

parallel through the spatial channels.


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3.5 Simulation Tool

In order to reach our objectives we use the Network Simulator 2 (NS2) which has the

necessary base structure for simulating many kinds of computer networks including IEEE802.11 based wireless networks which is the framework for our thesis.

NS2 is written in C++ and OTcl (Tcl script with Object Oriented extensions). It can

interpret Tcl scripts and has a scheduler of simulation events and object libraries of network

components, and network setup module libraries that are referred as plumbing simulator

objects (Figure 4.a). Generally, to use NS2, we program in OTcl script language that has to

initiate an event scheduler, sets up the network topology using network objects and the

plumbing functions, where Plumbing means connect possible data paths among network

objects in order to set up a network. The power of NS2 comes from this plumbing because it

simplifies the simulation configuration. Moreover, it is possible to modify and implement

libraries in C++ which makes NS2 more efficient and powerful. In this manner we are able to

implement designs of new architectures by adding, modifying or creating new protocols and

functions which can be linked and called from Tcl scripts where different scenarios can be set

up.

Fig 3.7: Users view of Ns2


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Network simulator 2 (NS-2) is an open source discrete event simulation tool used for

simulating Internet protocol (IP) networks. It was developed by UC Berkeley and widely used

worldwide for network simulation purposes. The NS-2 software uses TCL as a front-end

interpreter and C++ as the back end network simulation engine. Network simulation scripts in

TCL are used to create the network scenarios and upon the completion of the simulation, trace

files that capture events occurring in the network are produced. The trace files would capture

information that could be used in performance study, e.g. the amount of packets transferred

from source to destination, the delay in packets, packet loss etc.

3.5.1 NS2 TRACE FILE

The trace data is in ASCII code and are organized in 12 fields as shown in Fig.3.8.

Fig3.8: Trace data fields

Each trace line starts with an event descriptor followed by the simulation time (in seconds) of

that event, and from and to node, which identifies the link on which the event occurred. The

next information in the line are for flags. Since no flags are set here we have ----". Then we

have the packet type and size (in Bytes). The next field is flow id (fid) of IP address that a user

can set for each flow. Even though fid field may not be used in a simulation, users can use this

field for analysis purposes. The next two fields are source and destination address in forms of

"node. port". The last field shows the network layer protocol's packet sequence number. Note

that even though UDP implementations do not use sequence number, NS-2 keeps track of UDP

packet sequence number for analysis purposes. The last field shows the unique id of the packet.

However, the trace file is just a block of ASCII data in a file and quite cumbersome to access

using some form of post processing technique.

In order to ease the process of extracting data for performance study, the NS-2 Trace

Analyzer is proposed. This software is a tool for extracting and presenting trace files for the

network simulation environment of NS-2. The NS-2 Trace Analyzer software consists of three


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layers as shown in figure 3.9. The first layer is the source layer which consists of the trace file

data. The second layer is the processing layer. This layer processes the data obtain from the

source and convert it to meaningful format for the third layer. The third layer is the

presentation layer. This layer presents meaningful data in the form of graph, table and report

for network performance study, i.e. throughput, end-to-end delay, packet loss and jitter.

Fig3.9 :NS2 trace analyzer layers

Through the NS-2 Trace Analyzer the user would be able to do performance study of anetwork scenario through interactive GUI. This will benefit the user since he or she can

concentrate on developing new algorithms or new architectures rather spending too much time

on post processing of data.


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CHAPTER 4

DISSERTATION WORK IN

PROGRESS


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Chapter 4

NS2 undoubtedly is a very powerful network simulator that has been used widely. However,

unfortunately it does not provide tools to represent results. To simulate a certain network

scenario, NS-2 users need to write a simulation script, save it and invoke the NS2 interpreter.

After that NS-2 will simply store the results in form of trace files. There are two types of trace

files.

This means that the NS-2 user will end up creating their own program to process the

trace files to represent it in a presentable form. One popular approach is to produce two types of

trace file, i.e. network animation (NAM) trace file and normal trace file. NAM trace file is used

for network animation purposes. While for trace file processing, a program can be coded using

the users own favorite software and graph plotters like GNU plot and xgraph can be used to

view the results. Fig.4.1 shows the approach taken.

Fig.4.1: Ns-2 Simulation Process Flow


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4.1 THE SIMULATION CONFIGURATION

In this section, we illustrate the network configuration of our simulation study. We consider a

25-node MCMR WMN backbone in which all nodes are stationary and they are not required

to have the same number of radio interfaces. All nodes are mesh routers and node 12 acts as a

central mesh router that could be connected to a wired network, as shown in Figure 4.2.Our

main goal is to evaluate the throughput and delay performance of packet aggregation under

MCMR wireless ad hoc networks. Our WMN design has the following assumptions and

features:

24 nodes transmit frames to the central mesh router through other mesh routers

in a multi-hop manner. The path or flow from any node to the central mesh router can be built using up

to four channels.

We consider four MCMR scenarios on the same network topology. In the first

scenario, we assign only one channel at each node. From the second to the fourth

scenario, two to four channels can be used, respectively.

Fig 4.2 Topology of a 25 node network


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CONCLUSIONS

We have studied the performance of MCMR wireless ad hoc network under IEEE

802.11n.Better network performance canbe

obtained by using more channels, aggregationof more packets per frame, and appropriate channel assignment. Then we have discussed the

mathematical tool which we will use to compare the performances of ad hoc network that is

Network Simulator 2(NS2). The NS-2 particularly popular in the ad hoc networking

community, and protocols used in ad hoc networks have been supported. The basic idea & use

of the simulator is studied .


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REFERENCES

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mac protocol for high-data-rate ultra wideband ad hoc networks in Vehicular Technology,

IEEE Transactions on, volume 56, pages 312321.

Raniwala A. and Chiueh T.C.[2005], Architecture and algorithm for an IEEE 802.11

based multi-channel wireless mesh network. in Proc. of IEEE INFOCOM05,volume 3,

pages 2223-2234.

S Merlin[2007], Resource allocation in multi-radio multichannel wireless ad hoc

networks. On line available http://www.dei.unipd.it/merlo/papers/mc4.pdf Technical

Report.

A.K. Das, H.M.K. Alazemi, R. Vijayakumar, and S. Roy[2005], Optimization models

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and Ad Hoc Communications and Networks, 2005. IEEE SECON 2005. Second Annual

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Almeroth K.C. ,Ramachandran K.N., Beldin E.M. and Buddhikot M.M [2006],

Interference-aware channel assignment in multi-radio wireless mesh network,

INFOCOM,2006.
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zohaib 3rd seminar report

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