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1

CONTENTS



























Page.
n
o


Chapter 1:

Introduction to Wireless Networks


1
-
13

1.1

Wireless networks






1
-
3

1.2

Topologies in Network Design




4
-
8

1.3

Mesh Network Configurations




8
-
9

1.4

Comparison of WMNs w
ith other Networks



9
-
13


Chapter 2:

Literature Survey on Wireless mesh networks


14
-
41



2.1

Description







14
-
22




2
.2




Case study on Wireless Mesh Networks : A survey


23
-
24

2.2
.
1


Network Architecture





24
-
27

2
.
2.2


Characteristics






28
-
29

2.
2.3


Application scenarios





29
-
36

2.
2.4


Critical factors






36
-
38

2
.
2.5


Multichanne
l wireless mesh
networks



39

2
.
2
.
6


MAC and Sma
rt antennas





39
-
40

2.2
.
7


Architecture







41
-
42


Chapter 3
:

Challenges in Different Layers





43
-
51



3
.1 Physical Layer







43


3
.1.1


Physical and logical meshes





43



3
.1.2

Intra

and Extra Mesh






44

3
.1.3 Advanced physical layer

Techniques




45
-
47

3
.1.4 Open research issues






47

Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25


3
.2 Medium Access Control




47
-
48

3
.3


Routing







48
-
50

3
.4

Transport and Applications





50
-
51

C
hapter 4
:

Summary of potential mesh pitfalls to avoid

52
-
57

4
.1 Capacity








52

4
.2 Infrastructure







53

4
.3 Efficiency







53

4
.4 Relay exhaustion






54

4
.5 Initial roll
-
out







54

4
.6 Upgradeability







54

4
.7

R
eliance of the system on user





55

4
.8 Adhoc versus quality of service





56

4
.9 Security and trust






56
-
57


Chapter 5
:

Successful Mesh Implementations




58
-
61

5
.1 Wireless cities







58

5
.2 Community Internet






59

5
.3 Vehic
ular Adhoc network





60
-
61


Conclusion

and Future Work




62
-
63

References








64
-
75

Publications







76





Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25


ABSTRACT

Wireless Mesh Networks is a new exciting technology that is anticipated to resolve the
limitations and to signif
icantly improve the performance of adhoc networks ,wireless
local area networks(WLANS),wireless personal area networks(WPANS), and wireless
metropolitan area networks(WMANs).Wireless Mesh Network is a decentralized
networking technology that is currently

being adapted to connect peer
-
to
-
peer clients
and large
-
scale backbone networks. It will deliver wireless services for a large variety
of applications in personal, local, campus, and metropolitan areas. Wireless Mesh
Networks (WMNs) consist of mesh router
s and mesh clients, where mesh routers have
minimal mobility and form the backbone of WMNs. They provide network access for
both mesh and conventional clients. Mesh routers have bridging and gateway
functionality that in turn helps in the integration of W
MNs with other existing networks
such as internet, cellular, IEEE 802.15, IEEE 802.16, sensor networks , etc. However
mesh clients can be either stationary or mobile and form a client mesh network among
themselves and with mesh routers.

In WMNs, nodes a
re comprised of mesh routers and mesh clients. Each node operates
not only as a host but also as a router, forwarding packets on behalf of other nodes that
may not be within direct wireless transmission range of their destinations. A WMN is
dynamically sel
f
-
organized and self
-
configured, with the nodes in the network
automatically establishing and maintaining mesh connectivity among themselves
(creating, in effect, an ad hoc network). This feature brings many advantages to WMNs
such as low up
-
front cost, ea
sy network maintenance, robustness, and

reliable service
coverage. Conventional nodes (e.g., desktops, laptops, PDAs, Pocket

PCs, phones, etc.)
equipped with wireless network interface cards (NICs) can connect directly to wireless
mesh routers. Customers w
ithout wireless NICs can access WMNs by connecting to

Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25


wireless mesh routers through, for example, Ethernet. Thus, WMNs will greatly help the
users to be always
-
on
-
line anywhere anytime.

Moreover, the gateway/bridge
functionalities in mesh routers enable
the integration of WMNs with various existing
wireless networks such as cellular, wireless sensor, wireless
-
fidelity (Wi
-
Fi)
,

worldwide
inter
-
operability for microwave access (Wi

MAX)
, Wi

Media

networks. Consequently,
through an integrated WMN, the users o
f existing network can be provided with
otherwise impossible services of these networks.


WMN is a promising wireless technology for
numerous applications
, e.g., broadband
home networking, community and neighbo
u
rhood networks, enterprise networking,
buildi
ng automation, etc. It is gaining significant attention as a possible way for cash
strapped Internet service providers (ISPs), carriers, and others to roll out robust and
reliable wireless broadband service access in a way that needs minimal up
-
front
inves
tments. With the capability of self
-
organization and self
-
configuration, WMNs can
be deployed incrementally, one node at a time, as needed.

Mesh networks provide a number of applications. For example in difficult environments
such as emergency situations,
tunnels, oil rigs, battlefield surveillance, high speed
mobile video applications on board public transport or real time racing car telemetry.
Some current applications are:

1.

U.S. militar
y forces are now using wireless mesh networking

to connect their
compu
ters, mainly ruggedized laptops, in field operations.

2.

Electric meters now being deployed on residences transfer the
ir readings from one
to another
and eventually to the central office for billing without the
need for human
meter readers or
the need to conn
ect the meters with cables
.

3.


The laptops in the
one laptop per child
program use wir
eless mesh networking to
enable


students to exchange files and get on the Internet even though they lack wired
or cell phone or other physical connections in their area.

4.

B
roadband home networking.

5.

Community and neighbourhood networking.

Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25


6.

Enterprise networking.

7.

Metropolitan area networks.

8.

Transportation systems

9.

Building automation


10.
Health and medical systems
.


11.

Security surveillance systems


12.

P2P Communications



H
owever, to make a WMN be all it can be, considerable research efforts are still
needed. For example, the available MAC and routing protocols applied to WMNs do
not have enough scalability; the throughput drops significantly as the number of nodes
or hops i
n a WMN

increases. Similar problems exist in other networking protocols.
Also a

number of research challenges remain in all protocol layers.
Consequently, all
existing protocols from the application layer to transport, network MAC, and physical
layers need

to be enhanced or re
-
invented. Researchers have started to revisit the
protocol design of existing wireless networks, especially of IEEE 802.11 networks, ad
hoc networks, and wireless sensor networks, from the perspective of WMNs. Industrial
standards gro
ups are also actively working on new specifications for mesh networking.
For example, IEEE 802.11, IEEE 802.15, and IEEE 802.16

all have established sub
-
working groups to focus on new standards for WMNs.

New modulation scheme
s need to be developed i
n orde
r to a
chieve higher transmission
rate. For e.g.,

new wideband transmission schemes other than
OFDM
and
UWB
are
needed.

Advanced antenna processing including
directional
,
smart

an
d multiple antenna

technologies is further investigated, since their complexit
y and cost are still too high for
wide commercialization.

Several other efforts are needed in fields like flexible spectrum management, cross
layer design etc.


Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25







CHAPTER
-
1


An Introduction to Wireless
networks








Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25




CHAPTER
-
1


An Introduction

to

Wireless networks



1.1
INTRODUCTION


Wireless network

refer to any type of computer network that is not connected by cables
of any kind. It is a method by which telecommunications network and enterprise
(business), installations avoid the costly proce
ss of introducing cables into to a building,
or as a connection between various equipment locations. Wireless telecommunications

networks are generally implemented and administered using a transmission system
called radio waves (
Radio waves

are a type of e
lectromagnetic radiation with
wavelengths in the electromagnetic spectrum longer than infrared light).


Wireless networking is used to meet many needs. Perhaps the most common use is to
connect laptop users who travel from location to location. Another co
mmon use is for
mobile networks that connect via satellite. A wireless transmission method is a logical
choice to network a LAN segment that must frequently change locations. The following
situations justify the use of wireless technology:



To span a distan
ce beyond the capabilities of typical cabling,



To provide a backup communications link in case of normal network failure,



To link portable or temporary workstations,



To overcome situations where normal cabling is difficult or financially impractical, or



To

remotely connect mobile users or networks.

Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25


Types of wireless connections

Wireless PAN:

Wireless Personal Area Networks (WPANs) interconnect devices
within a relatively small area, generally within a persons reach. For example, both
Bluetooth radio and in
visible Infrared light provides a WPAN for interconnecting a
headset to a laptop.

Wireless LAN:

W
ireless local area network (WLAN) links two or more devices using
a wireless distribution method, providing a connection through an access point to the
wide
r internet. The use of spread
-
spectrum technology also gives users the mobility to
move around within a local coverage area, and still remain connected to the network.
"Wi
-
Fi" is a term used to describe 802.11 WLANs, although it is technically a declared
s
tandard of interoperability between 802.11 devices.

Wireless MAN:

Wireless Metropolitan Area Networks are a type of wireless network
that connects several Wireless LANs. WiMAX is a type of Wireless MAN and is
described by the IEEE 802.16 standard.

Wireless

WAN:

Wireless wide area networks are wireless networks that typically
cover large areas, such as between neighboring towns and cities, or city and suburb.
These networks can be used to connect branch offices of business or as a public internet
access syst
em. The wireless connections between access points are usually point to
point microwave links using parabolic dishes on the 2.4

GHz band, rather than omni
directional antennas used with smaller networks. A typical system contains base station
gateways, acc
ess points and wireless bridging relays. Other configurations are mesh
systems where each access point acts as a relay also.


Uses

Wireless networks continue to develop, usage has grown in 2010. Some examples of
usage include Cellular phones which are par
t of everyday wireless networks, allowing
easy personal communications. Another example, Inter
-
continental network systems,
use radio satellites to communicate across the world. Emergency services such as the
police utilize wireless networks to communicate

effectively as well. Individuals and
businesses use wireless networks to send and share data rapidly, whether it be in a small

Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25


office building or across the world.

In a general sense, wireless networks offer a vast
variety of uses that are transmitted t
hrough different forms of media commonly used by
both business and home network. Some of the obvious uses of wireless networks are:

Space:

Space is just as important a characteristic of wireless networking uses as any of
the others mentioned in this sectio
n. Wireless networks offer many advantages when it
comes to difficult
-
to
-
wire areas trying to communicate such a
s across a street or river, a
ware
house on the other side of the premise or buildings that are physically s
eparated but
operate as one
. Wireless

networks allow for users to designate a certain space which the
network will be able to communicate with other devices through that network. Space is
also created in homes as a result of eliminating the clutters of wiring that

once
acquainted networking
.
This technology allows for an alternative to installing physical
network mediums such as TPs, coaxes, Fiber
-
optics, etc. which can also be extremely
expensive for large corporations.

Business:

Organizational e
nd users are continuing to inte
grate wireless L
ANs into
corporate information systems to support a broader base of applications. These uses of
wireless networking are now seen as practical and cost effective for companies to
compete in a global market. Wireless technologies are applicable to all indust
ries,
especially for those that stress immediate processing. These industries are finding
creative and innovating ways to place portable computers in industry
works

that are
hands on such as doctors, nurses, warehouse clerks, inspectors, claims adjustors,
real
estate
agents, and so on
.

By using wireless technology, businesses are able to couple
portable devices with a database and specific applications which

in turn meet mobility
needs
. Ultimately this eliminates paper work, decreases errors, reduces proces
s cost,
and improves efficiency which are all pluses in
today’s

economical climate.

Home:

For homeowners, wireless technology is an effective option as compared to
Ethernet

for sharing printers, scanners, and high speed internet connections. WLANs
help sav
e from the cost of installation of
cable

mediums, save time from physical
installation, and also creates mobility for devi
ces connected to the network
. Wireless
networks can make multi
-
tasking at home much more convenient or relaxing once the
network has b
een setup and configured to your liking. The best advantage of WLANs is
that they are simple and require one single access point connected directly to the
internet via a router.

Once a machine or device is connected to your wireless network
you can access the
World Wide Web

from anywhere in the house within the router's
range.

Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25


1.2
Topology in Network Design


In computer networking,
topology

refers to the layout of connected

devices. Following
are the standard topologies of networking. A topology may be thought of as a network's
virtual shape or structure.

Network topologies are categorized into the following basic
types:



Bus



Ring



Star



Tree



Mesh

More complex networks ca
n be built as hybrids of two or more of the above basic
topologies.

Bus Topology



Fig. 1

Bus networks use a common backbone to connect
all devices. A single cable which acts
as the backbone, functions as a shared communication medium that devices attach or
tap into with an interface connector. A device wanting to communicate with another
device on the network sends a broadcast message ont
o the wire that all other devices
see, but only the intended recipient actually accepts and processes the message.

Ethernet bus topologies are relatively easy to install and don't require much cabling
compared to the alternatives. However, bus networks wor
k best with a limited number

Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25


of devices. If more than a few dozen computers are added to a network bus,
performance problems will likely result. In addition, if the backbone cable fails, the

entire network effectively becomes unusable.

Ring Topology





Fig. 2


In a ring network, every device has exactly two neighbors for communication purposes.
All messages travel through a ring in the same di
rection (either "clockwise" or
"counterclockwise"). A failure in any cable or device breaks the loop and can take down
the entire network.


To implement a ring network, one typically uses FDDI, SONET, or Token Ring
technology. Ring topologies are found in

some office buildings or school campuses.

Star Topology

Many home networks use the star topology. A star network features a central
connection point called a "hub" that may be a hub, switch or router. Devices typically
connect to the hub with Unshielded
Twisted Pair (UTP) Ethernet.


Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25





Fig. 3


Compared to the bus topology, a star network generally requires more cable, but a
failure in any star network ca
ble will only take down one computer's network access
and not the entire LAN. (If the hub fails, however, the entire network also fails.)

Tree Topology




Fig. 4



Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25


Tree topologies integrate multiple star topologies together onto a bus. In its simplest
form, only hub devices connect directly to the tree bus and each hub functions as the
"root" of a tree of devices. This bus/star hybrid appr
oach supports future expandability
of the network much better than a bus (limited in the number of devices due to the
broadcast traffic it generates) or a star (limited by the number of hub connection points)
alone.

Mesh Topology



Fig. 5


Mesh topologies involve the concept of routes. Unlike each of the previous topologies,
messages sent on a mesh network can take any of several possible paths fr
om source to
destination. Some WANs, most notably the Internet, employ mesh routing. A mesh
network in which every device connects to every other is called a full mesh. Partial
mesh networks also exist in which some devices connect only indirectly to other
s.


1.3
Mesh networks

Mesh networking (topology)

is a type of networking where each node must not only
capture and disseminate its own data, but also serve as a
relay

for other sensor nodes,
that is, it must collaborate to propagate the data in the networ
k.

The core advantage of
wireless mesh networks is their inherent ability to form a network on power up.

The


Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25


nodes hear each other's broadcast and form a network.
Also when a node fails and
the
nodes discover an alternate routing path. This healing is f
ully automatic.

Over the years, wireless mesh networking has seen three unique deployments based on
radio technology, each incorporating iterative improvements allowing for greater
scalability and higher network performance .This early stage of pre IEEE st
andard
technological development is known as first Generation of Wireless Mesh. The
following deployments are briefly described of various configurations of first
generation Wireless Mesh Networking:


Configurations

1.

Radio Mesh
:

This configuration uses on
e radio

channel
(
Radio

is the transmission of signals by
modulation of electromagnetic waves with frequencies

below those of visible light)
,
both to service clients and to provide the mesh routing path back to a wired or satellite
link (backhaul). The sing
le mesh radio, provides both services
-

client access and
backhaul. Comparative performance analysis indicates this architecture provides the
worst performance of all configurations, because backhaul and service compete for
bandwidth. Also all single radio

mesh architectures suffer from the send
-
receive
-
wait
cycle. Since there is only radio, the mesh node has to listen, then send, then listen again.
This intermittent stop
-
and
-
go behavior adversely affects network performance
especially if the destination is

far away and the traffic has to be re
-
transmitted ("hop")
across many intermediate nodes first.


2.

Dual
-
Radio with 1
-
Radio backhaul mesh:

This configuration can also be referred to as a "1+1" network, since each node contains
two radios, one to provide serv
ice to the clients, and one for backhaul. The "1+1"
appellation indicates that these radios are separate
-

the radio providing service does not
participate in the backhaul, and the radio participating in the backhaul does not service
clients. These two rad
ios can operate in different bands. For example, a 2.4

GHz 802.11
b/g radio can be used for service and an 802.11a (5

GHz) radio can be used for
backhaul.


Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25


Most mesh products available today fall into this category. Separating service from
backhaul improv
es performance when compared with single
-
radio ad hoc mesh
networks. But since a single
-
radio mesh is still servicing the backhaul, packets traveling
toward
s

the Internet share bandwidth at each hop along the backhaul path with other
i
nterfering mesh backh
aul nodes,

all
-
operating on the same channel. This degrades
through

put, which are not as severe as for the single
-
radio mesh, but which are sizeable
nevertheless. Second generation mesh products are best employed in 1 or 2 hop
configurations.

3.

2
-
R
adio back
hauls

The last configuration is one that provides separate backhaul and service functionality
and dynamically manages channels of all of the radios so that all radios are on non
-
interfering channels. Performance analysis indicates that this provides the be
tter
performance than the other two methods considered here. Note that the two backhaul
radios for the 3
-
radio configuration are of the same type
-

not to be confused with 1+1
so
-
called dual radio meshes where one radio is typically of type 802.11 a (backh
aul)
and the other of type 802.11 b/g (service). In the 3
-
radio configuration, 2 radios provide
up link and down link backhaul functionality, and the other radio services clients.


1.4

Comparison of

WMNs
with other Networks

When we access the Internet via

WLAN (wireless local area network) at an airport, or
in our office, the device that we may use, such as a laptop or PDA, wirelessly connect
to one of many APs (access points) on the WLAN where each AP must have a physical,
wired connection to a network. T
he difference in a wireless mesh
network

is
,

the
majority of the APs don't have a hard
-
wired connection
.

Instead, they route traffic
wirelessly, and are connected to the network through a few, select, wired nodes.

In a large city, hundreds or even thousan
ds of nodes would be needed. A significant
amount of time and expense may be involved in installing all the cabling to create a
wired connection for each of the APs. Conversely, all that's needed for a mesh network
is installation of the AP. In most cases,

they're quickly and easily mounted on light
poles or traffic signals, which have ready supplies of power. The ease of installation and
low cost make wireless mesh networks an attractive choice; however, the ultimate
success of these installations lies in
the planning and design of the network.

Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25


Difference between Adhoc networks and WMNs

Based on their characteristics, WMNs are generally considered as a type of

adhoc
-
networks due to the lack of wired infrastructure that exists in cellular or Wi
-
Fi networks
through deployment of base stations or access points. While adhoc
-
networking
techniques are required by WMNs, the additional capabilities necessitate more
sophisticated algorithms and design principles for realization of WMNs. More
specifically instead bei
ng a type of adhoc networking, WMNs aim to diversify the
capabilities of adhoc networks. Consequently adhoc
-
networks can be considered as a
sub
-
set of WMNs. To illustrate this point, the differences between WMNs and adhoc
networks are outlined below.

1.4.1

Wirel
ess infrastructure/backbone:

As discussed before, WMNs consist of a wireless backbone with mesh routers. The
wireless backbone provides large coverage, connectivity, and robustness in the wireless
domain. However the connectivity in adhoc networks depends

on the individual
contributions of end
-
users which may not be reliable.

1.4.2

Integration:


WMNs support conventional clients that use the same radio technologies as a mesh
router. This is accomplished through a host
-
routing function available in mesh routers.
WMNs also enable integration of various existing networks such as Wi
-
Fi, the Internet,
cellular, and sensor networks through gateway/bridge functionalities in the mesh
routers. Consequently users in one network are provided with services on other
networks,

through the use of wireless infrastructure. The integrated wireless networks
through WMNs resemble the internet backbone, since the physical location of network
nodes becomes less important than the capacity and network topology.

1.4.3

Dedicated routing and con
figuration:


In adhoc networks, end
-
user devices also perform routing and configuration
functionalities for all other nodes. However, WMNs contain mesh
-
routers for these
functionalities. Hence, the load on the end
-
user is significantly decreased, which
pro
vides lower energy consumption and high
-
end application capabilities to possibly
mobile and energy constrained end
-
users. Moreover, the end
-
user requirements are
limited which decreases the cost of devices that can be used in WMNs.


Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25


1.4.4

Multiple radios:

Mesh
routers can be equipped with multiple radios to perform routing and access
functionalities. This enables separation of two main types of traffic in the wireless
domain. While routing and configuration are performed between mesh
-
routers, the
access to the n
etwork by end
-
users can be carried out on a different radio. This
significantly improves the capacity of the network. On the other hand, in adhoc
networks, these functionalities are performed in the same channel, and as a result, the
performance decreases.


1.4.5

Mobility:


Since adhoc networks provide routing using the end user
-
devices, the network topology
and connectivity depend on the movement of users. This imposes additional challenges
on routing protocols as well as on network configuration and deployment.

Mesh
networking is

a way to route data, voice and instructions between nodes.

It allows
for continuous connections and reconfiguration around broken or blocked paths by
hopping from node to node until the destination is reached. Mesh networks
differ from

other networks in that the component parts can all connect to each other via multiple
hops,

and they generally are not

mobile.

Mesh

networks can be seen as a type of adhoc
networks.

Mobile adhoc networks (MANETS), and mesh networks are therefore closely
re
lated, but
Manets

also have to deal with the problems introduced by the mobility of
the nodes.



Mesh networks are
self
-
healing: the

network can still operate even when a node breaks

down or a connection goes bad. A
s a
result, a

very reliable network is
fo
rmed.
Depending

on the way the nodes are
connected,

mesh networks are classified
as:

(1)

F
ully connected
,

(2) Partially connected


(1)Fully connected: it is

a

type of network topology in which each of the nodes of the
network is

connected to each of the
other nodes in the network

with a point
-

to
-

point
link. This makes it possible for data to be simultaneously transmitted from any single
node to all of the other
nodes. The

physical fully connected mesh topology is generally
too costly and complex for pra
ctical
networks, although

the topology is
used when there

are only a small number of nodes to be interconnected.

(2)

Partially
connected: it

is a type of network topology in which some of the nodes of
the network are connected to more than one other node i
n the network with a point
-

to
-
point link
. This makes it possible to take advantage of some of the redundancy that is

Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25


provided by a physical fully connected mesh topology without the expense and
complexity required for a connection between every node in
the network.


In most practical networks that are based upon the physical partially connected mesh
topology, all of the data that is transmitted between nodes in the network takes the
shortest path (or an approximation of the shortest path) between nodes,
except in the
case of failure or break in one of the links, in which case the data takes an alternate path
to the destination. This requires that the nodes of the network possess some type of
logical

‘routing’ algorithm to determine the correct path to use

at any particular time.

In a partially connected mesh topology, there are at least two nodes with two or more
paths
between them to provide redundant paths to be used in case the link providing one
of the
paths fails. This

decentralisation is often used t
o
compensate for

the single
-
point
-
failure disadvantage that is
present when

using a single device as a central
node (
e.g.in
star and tree networks.).
A

special kind of
mesh, limiting

the number of hops between
two nodes, is a
hypercube. The numbers of arbit
rary forks in mesh

networks

makes
them more difficult to design and implement, but their decentralization nature makes
them very useful. This is similar in some ways to a grid network, where a ring or linear
topology is used to connect systems in multiple
directions.


A fully connected network, complete topology or full mesh topology is a network
topology in which there is a direct link between all pair of nodes. In a fully connected
network with n
nodes, there are n

(n
-
1)/2 direct links. Networks designed
with this
topology are usually very expensive to set up, but provide a very high degree of
reliability due to the multiple paths for data that are provided by the large number of
redundant links between nodes. This topology is mostly seen in military appli
cations.
However,

it can also be
seen in the file sharing protocol Bit Torrent in which users
connect to other users in the “swarm” by allowing each user sharing the file to connect
to other users also involved. Often
in actual

usage of Bit Torrent any giv
en individual
node is rarely connected to every other single node as in a true fully connected network
but the protocol does allow for the possibility foe any one node to connect to any other
node when sharing files.


Mesh networking is a way to route dat
a, voice and instructions between nodes. It
a
llows

for
continuous connections and reconfiguration around broken or blocked paths
by “hopping” from node to node until the destination is reached. Mesh networks differ
from other networks in that the component

parts can all connect to each other via
multiple hops, and they generally are not mobile. Mesh networks can be seen as a type
of adhoc networks. Mobile adhoc networks (MANETS) and mesh
networks are,


Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25


therefore

closely
related, but

MANETs
also have

to de
al with the problems introduced
by
the mobility of the nodes.



F
ig
. 5


Wireless mesh connectivity






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ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25







CHAPTER
-
2


Literature Survey on Wir
eless mesh
networks












Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25


CHAPTER
-
2

Literature Survey on

Wireless mesh
networks


2.1

Description


In recent years, many researchers have done research on wireless mesh networks.

Following are some

articles/journals highlighting research on various fa
cts on WMN.


Wireless mesh networks
(WMNs) have emerged as a promising concept to meet the
challenges in next
-
generation networks such as providing flexible, adaptive, and
reconfigurable architecture while offering cost
-
effective solu
tions to the service
p
roviders
. Unlike traditional Wi
-
Fi networks, with each
access point
(AP) connected to
the wired network, in WMNs only a subset of the APs are required to be connected to
the wired network. The APs that are connected to the wired network are called the
Int
ernet gateways
(IGWs), while the APs that do not have wired connections are called
the
mesh routers
(MRs).The MRs are connected to the IGWs using multi
-
hop
communication. The IGWs provide access to conventional clients and interconnect ad
hoc, sensor, cell
ular, and other networks to the Internet.

Some of the important challenges in designing routing protocols for WMNs are
discussed in the literature. At the top layer, are the
Internet gateways
(IGWs) which are
connected to the wired Internet. They form the

backbone infrastructure for providing
Internet connectivity to the elements in the second level. The entities at the second level
are called wireless
mesh routers
(MRs) that eliminate the need for wired infrastructure
at every MR and forward their traffic

in a multi
-
hop fashion towards the IGW. At the
lowest level are the
mesh clients
(MCs) which are the wireless devices of the users.
Internet connectivity and peer
-
to
-
peer communications inside the mesh are two
important applications for a WMN. Therefore,
design of an efficient and low overhead
routing protocol that avoids unreliable routes, and accurately estimate the end
-
to end
delay of a flow along the path from the source to the destination is a major challenge.

Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25


Some of the major challenges in designin
g routing protocol for WMNs are discussed. It
has been observed by Lundgren and Nordstorm in 2002 that in wireless ad hoc networks
like WMNs, nodes receiving broadcast messages introduce communication gray zones.
In such zones, data messages cannot be exch
anged although the hello messages reach
the neighbours. This leads to disruption in communication among the nodes. Since the
effective bandwidth of wireless channels vary continuously, reduction of control
overhead is important in order to maximize through
put in the network. Extensive work
has been done in the area of secure unicast routing in multi
-
hop wireless networks by
Hu in 2002a; Hu in 2002b; Sanzgiri in 2002; Marti in 2000;Papadimitratos in 2003a;
Awerbuch in 2002; Awerbuch in 2005).

The typical wo
rk on WMNs started in 2005 with

a publication of Akyildiz, I.F. and
Xudong Wang in 2005
. According to their publication

Wireless mesh networks
(WMNs) consist of mesh routers and mesh clients, where mesh routers have minimal
mobility and form the backbone
of WMNs. They provide network access for both mesh
and conventional clients. The integration of WMNs with other networks such as the
Internet, cellular, IEEE 802.11, IEEE 802.15, IEEE 802.16, sensor networks, etc., can
be accomplished through the gateway a
nd bridging functions in the mesh routers.
WMNs are anticipated to resolve the limitations and to significantly improve the
performance of ad hoc networks, wireless local area networks (WLANs), wireless
personal area networks (WPANs), and wireless metropol
itan area networks (WMANs).
WMNs will deliver wireless services for a large variety of applications in personal,
local, campus, and metropolitan areas. This paper presents a detailed study on recent
advances and open research issues in WMNs. System archite
ctures and applications of
WMNs are described, followed by discussing the critical factors influencing protocol
design. Theoretical network capacity
is

explored with an objective to point out a number
of open research issues.
WMN can be considered as a typ
e of wireless ad
-
hoc network
because nodes can automatically establish network and maintain the connectivity in an
ad
-
hoc manner. In addition, the WMN can also be dynamically self
-
organized and self
-
configured.



WMNs have become the focus of research in r
ecent years, owing to their great promise
in realizing numerous next
-
generation wireless services. Driven by the demand for rich
and high
-
speed content access,
mechanisms for WMNs are presented in the literature. A
few novel secure routing mechanisms that
take into account application QoS while
detecting malicious and selfish nodes are also discussed.

In many deployment
situations, WMNs are designed to be integrated with other types of networks, such as
wired networks and cellular networks.

Recent

research
on WMNs has focussed on
developing high performance communication protocols. However, given the wireless

Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25


and multi
-
hop nature of the communication, WMNs are subject to a wide range of
security threats. A large number of security issues at various layers
of WMNs have been
presented with a particular focus on the network layer.

In 2006
Bo Han and Weijia Jia

proposed a

collision
-
free centralized scheduling
algorithm for IEEE 802.16 based Wireless Mesh Networks (WMN) to provide high
-
quality wireless multimed
ia services. They designed a relay strategy for the mesh nodes
in a transmission tree, taking special considerations on fairness, channel utilization and
transmission delay. They evaluated the proposed algorithm with four selection criteria
through exte
nsive simulations and the experimental results were instrumental

for
improving the performance of IEEE 802.16 based WMNs in terms of link scheduling.


In 2006 Aoun, B.;

Boutaba, R.

and


Youssef Iraqi presented a paper on
Gateway
-
Placement Optimization i
n Wireless Mesh Networks With QoS Constraints. According
to their journal i
n a wireless mesh network (WMN), the traffic is aggregated and
forwarded towards the gateways. Strategically placing and connecting the gateways to
the wired backbone is critical to

the management and efficient operation of a WMN. In
this paper, they address the problem of gateways placement, consisting in placing a
minimum number of gateways such that quality
-
of
-
service (QoS) requirements are
satisfied. T
hey

proposed a polynomial ti
me near
-
optimal algorithm which recursively
computes minimum weighted Dominating Sets (DS), while consistently preserving QoS
requirements across iterations. They evaluated the performance of their algorithm using
both analysis and simulation, and showed t
hat it outperforms other alternative schemes
by comparing the number of gateways placed in different scenarios.

In 2006 yet another paper was presented by
Yanchao Zhang and Yuguang Fang in which
they proposed
an Attack
-
Resilient Security Architecture for M
ultihop Wireless Mesh
Networks.

This paper addresses the security of WMNs, which is a key impediment to
wide
-
scale deployment of WMNs. They first thoroughly identify the unique security
requirements of WMNs for the first time in the literature. Then prop
ose
d

ARSA, an
attack
-
resilient security architecture for WMNs. In contrast to a conventional cellular
-
like
solution, ARSA eliminates the need for establishing bilateral roaming agreements and
having real
-
time interactions between potentially numerous WMN o
perators. With ARSA
in place, each user is no longer bound to any specific network operator, as he or she ought
to do in current cellular networks. Instead, he or she acquires a universal pass from a
third
-
party broker whereby to realize seamless roaming a
cross WMN domains
administrated by different operators. ARSA supports efficient mutual authentication and
key agreement both between a user and a serving WMN domain and between users


Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25


served by the same WMN domain. In addition, ARSA is designed to be resi
lient to a
wide range of attacks.

Due to the recent research advances in WMNs as presented by Franklin and C. R. Murthy
in 2007, these networks have been used in numerous applications such as in home
networking, community and neighbourhood monitoring, secu
rity surveillance systems,
disaster management and rescue operations etc. As there is no wired infrastructure to
deploy in the case of WMNs, they are considered cost
-
effective alternative to
wireless
local area networks
(WLANs) and backbone networks to mob
ile clients. The existing
wireless networking technologies such as IEEE 802.11, IEEE 802.15, IEEE 802.16, and
IEEE 802.20 are used in the implementation of WMNs.

As WMNs become an increasingly popular replacement technology for last
-
mile
connectivity to th
e home networking, community and neighbourhood networking, it is
imperative to design an efficient resource management system for these networks.

Routing is one of the most challenging issues in resource management for supporting
real
-
time applications wi
th stringent
quality of service
(QoS) requirements. However,
most of the existing routing protocols for WMNs are extensions of protocols originally
designed for
mobile ad hoc networks
(MANETs) and thus they perform sub
-
optimally.
Moreover, most routing pro
tocols for WMNs are designed without security issues in
mind, where the nodes are all assumed to be honest. In practical deployment scenarios,
this assumption does not hold. In a community
-
based WMN, a group of MRs managed
by different operators form an ac
cess network to provide last
-
mile connectivity to the
Internet. Preserving scarce access bandwidth and power, as well as security concerns
may induce some selfish users to avoid forwarding data for other nodes, even as they
send their own traffic through t
he network. The selfish behaviour of an MR degrades the
performance of a WMN since it increases the latency in packet delivery and packet
drops and decreases the network throughput.

In 2007 H Skalli, S Ghosh, SK Das presented a journal on
Issues and Solut
ions for


Channel Assignment Strategies for Multiradio Wireless Mesh Networks. They presented
that

n
ext
-
generation wir
eless mobile communications would

be driven by converged
networks that integrate disparate technologies and services. The wireless mesh ne
twork
is envisaged to be one of the key components in the converged networks of the future,
providing flexible high
-

bandwidth wireless backhaul over large geographical areas.
While single radio mesh nodes operating on a single channel suffer from capacity

constraints, equipping mesh routers with multiple radios using multiple non
-
overlap
-

ping channels can significantly alleviate the capacity problem and increase the aggregate

Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25


bandwidth available to the network. However, the assignment of channels to the

radio
interfaces poses significant challenges. The goal of channel assignment algorithms in
multiradio mesh networks is to minimize interference while improving the aggregate
network capacity and maintaining the connectivity of the network. In this articl
e we
examine the unique constraints of channel assignment in wireless mesh networks and
identify the key factors governing assignment schemes, with particular reference to
interference, traffic patterns, and multipath connectivity. After presenting a taxon
omy of
existing channel as
signment algorithms for WMNs, they

describe a new channel
assignment scheme called MesTiC, which incorporates the mesh traffic pattern together
with connectivity issues in order to minimize interference in multi
-

radio mesh
networ
ks.

In
M
ay 2008 ,

Soumendra Nanda and David Kotz.

presented a journal on
Mesh
-
Mon:

A
Multi
-
Radio Mesh Monitoring and Management System
.
They presented that m
esh
networks are a potential solution for providing communication infrastructure in an
emergency. T
hey can be rapidly deployed by first responders in the wake of a major
disaster to augment an existing wireless or wired network. We imagine a mesh node
with multiple radios embedded in each emergency vehicle arriving at the site to form the
backbone of a
mobile wireless mesh. The ability of such a mesh network to monitor
itself, diagnose faults and anticipate problems are essential features for its sustainable
operation. Typical SNMP
-
based centralized solutions introduce a single point of failure
and are u
nsuitable for managing such a network. Mesh
-
Mon is a decentralized
monitoring and management system designed for such a mobile, rapidly
-
deployed,
unplanned mesh network and works independently of the underlying mesh routing
protocol. Mesh
-
Mon nodes are des
igned to actively cooperate and use localized
algorithms to predict, detect, diagnose and resolve network problems in a scalable
manner. Mesh
-
Mon is independent of the underlying routing protocol and can operate
even if the mesh routing protocol completely

fails. A novel aspect of our approach is
that we employ mobile users of the mesh, running software called Mesh
-
Mon
-
Ami to
ferry management packets between physically
-
disconnected partitions in a delay
-
tolerant network manner. The main contributions of thi
s paper are the design,
implementation and evaluation of a comprehensive monitoring and management
architecture that helps a network administrator proactively identify, diagnose and
resolve a range of issues that can occur in a dynamic mesh network. In exp
eriments on
Dart
-
Mesh, ou
r 16
-
node indoor mesh testbed, they

found Mesh
-
Mon to be effective in
quickly diagnosing and resolving a variety of problems with high accuracy, without
adding significant management overhead.

In 2008 another journal presented by L
iu Zhimin, Yang Yi, Xu Yingqing with the
increasing popularity and rising demand for high
-
rate wireless Internet access,

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ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25


traditional wireless access networks such as cellular network and Wireless Local Area
Network (WLAN) are facing some challenges. The
Wireless Mesh Network (WMN) is
emerging as a flexible and low
-
cost alternative to provide multi
-
hop communications,
supporting applications such as last
-
mile Internet delivery. The WMN has also become
a promising technology in the merging of wireless netwo
rks. Some key technologies for
the WMN networking, including network configuration, power control, mobility
management, access control, and routing protocols, are analyzed; the routing protocol
design in WMN and mobile Ad hoc network are compared. An examp
le of WMN
testbed based on WLAN and second
-
layer switching technology is given.

In 2008 another paper was presented by
Akyildiz, I.F. and Xudong Wang on Cross
-
Layer Design in Wireless Mesh Networks. According to their survey t
he conventional
layered
-
protoc
ol architecture does not provide optimal performance for wireless mesh
networks (WMNs). The method of optimization decomposition of the protocol stack can
achieve optimal network performance. This method usually results in a clean
-
slate
protocol architectu
re that is different from the protocol architecture of WMNs. Such a
difference actually demonstrates the need for a cross
-
layer design. Specific features
pertaining to WMNs also show the need for cross
-
layer optimization across different
protocol layers. I
n this paper, motivations for cross
-
layer design in WMNs are stated
first. Moreover, cross
-
layer optimization schemes and algorithms between different
protocol layers are investigated with an objective of shedding light on open research
problems and new ap
proaches. Guidelines for carrying out cross
-
layer design in WMNs
are also provided in this paper
.

According to survey of Dong in 2009, enforcing cooperation among the nodes in WMNs
is a critical issue and a routing protocol should make use of such a cooper
ation
enforcement scheme in order to ensure efficiency in packet forwarding and minimizing
packet drops. To enforce cooperation among nodes and detect malicious and selfish
nodes in self
-
organizing networks such as MANETs, various collaboration schemes
hav
e been proposed in the literature of Santhanam in 2009. Most of these proposals are
based on trust and reputation frameworks which attempt to identify misbehaving nodes
by an appropriate detection and decision making system, and then isolate or punish
them
. Unfortunately, most of these schemes are not directly applicable for WMNs due
to inherent differences in characteristics between MANETs and WMNs. Efficient,
reliable and secure routing protocols for WMNs are clearly in demand.

Several security vulnerabil
ities exist in the protocols for WMNs. According to the
literature presented by Shi in 2009, these vulnerabilities can be exploited by the
attackers to degrade the performance of the network. As with any radio
-
based medium,

Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25


the possibility of jamming att
acks in physical layer of WMNs is always there. Jamming
is a type of attack which interferes with the radio frequencies that the nodes use in a
WMN for communication. A jamming source may be powerful enough to disrupt
communication in the entire network.

In 2009 yet another paper was presented by
A N Le, D W Kum, Y Z Cho, and C K Toh
on Routing with Load
-
Balancing in multi
-
radio Wireless Mesh Networks.

This paper
addresses the interference and load imbalance problems in multi
-
radio infrastructure
mesh netw
orks, where each mesh node is equipped with multiple radio interfaces with a
subset of nodes serving as Internet gateways. To provide backbone support, it is
necessary to reduce interference and balance load in Wireless Mesh Networks (WMNs).
In this paper,

we proposed a new Load
-
Aware Routing Metric, called LARM, which
captures the differences in transmission rates, packet loss ratio, intra/inter
-
flow
interference and traffic load in multi
-
radio mesh networks. This metric is then
incorporated into their pro
posed load
-
balancing routing protocol, called LBM, so as to
provide load balancing for multi
-
radio mesh networks. Simulation results show that
LARM provides better performance when compared to WCETT and hop
-
count routing
metrics.

According to

the article of Ritu Malik and Meenakshi Mittal.published in February
2010, Wireless Mesh Network (WMN) is one of emerging technology of the next
generation networks, and it is going to address the internet provision to users at low cost
anytime from anywh
ere. Being a broadband wireless network of the future, still it is
facing a lot of technical and critical issues which are prohibiting it from the world wide
deployment and acceptance. Multi
-
hop nature of this broadband wireless technology
increases routin
g overhead and poor packet delivery ratio. In this paper, we present
firstly the detailed architecture of IEEE 802.11 WMN, and then a new architecture for
WMN is proposed, which consists two components, one is Mesh Backbone, the other is
Mesh Domain. Then
some security attacks on WMN and then a proposed architecture
which will solve most of the existing and the future problems. The main concerns of this
architecture is that its multi
-
hop nature and ad hoc connectivity amongst the nodes of
WMN with current a
s well as future prospective.

In may 2010
Nikhil Saxena and Mieso Denko
1
presented that

Wireless mesh networks
(WMNs) consist of dedicated nodes called mesh routers

which relay the traffic
generated by mesh clients over multi
-
hop
paths. According
to them in a community
WMN, all mesh routers may not be managed by an Internet Service Provider (ISP).
Limited capacity of wireless channels and lack of a single trusted
authority in such
networks can motivate mesh routers to behave selfishly by dropping relay traffic in

Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25


order to provide a higher throughput to their own users. Existing solutions for
stimulating cooperation in multi
-
hop networks use promiscuous monito
ring or exchange
probe packets to detect selfish nodes and apply virtual currency mechanism to
compensate the cooperating nodes. These schemes fail to operate well when applied to
WMNs which have a multi
-
radio environment with a relatively s
tatic top
ology. They

propose
d

architecture for a community WMN which can detect selfish behaviour

in the network and enforce cooperation among mesh routers. The architecture adopts a
decentralized detection scheme by dividing the mesh routers into manageable c
lusters.
Monitoring agents hosted on managed mesh routers monitor the


behaviour of mesh
routers in their cluster by collecting periodic reports and sending them to the sink
agents hosted at the mesh gateways.


In January 2011 Longjam Velentina and Shee
ba Praveen presented a journal on
Standard Activities of Wireless Mesh Networks .according to them Wireless Mesh
Networks (WMNs) are gaining increasing popularity due to its features like self
organization, self
-
configuration and self
-
healing. WMNs reduces

the authentication time
by up to a factor of 3 compared to WLAN, while allowing mobile stations to move
without performing additional authentications. Wireless Mesh Networks have been
envisioned as an important solution to the next generation wireless net
working.

As various standards are being specified for different mesh networking technologies in
many application areas. Among the various standard organizations, the IEEE standards
committee is the most enthusiastic at promoting WMN as a networking techno
logy in
all its aspects. IEEE 802 standards committee includes different working groups for
Personal Area Network (PAN), Local Area Network (LAN) and Metropolitan Area
Network (MAN) based WMNs. In this paper, we focus on IEEE 802 standards.


In 2011,

Luke Shillington

and
Daoqin Tong

presented that

wireless mesh netwo
rk
(WMN) technology allows data transmission from one node to another without
extensive cabling. In this article, spatial characteristics of maximal covering problems
are explored, and a novel spatial optimization model is proposed for WMN topology
plannin
g. The model selects the optimal locations for network infrastructure to achieve
the maximal coverage of spatial demand. Additionally, important WMN design
requirements have been accounted for, including network topology and throughput
capacity. The validi
ty of the model is tested through a WMN deployment developed
for an emergency medical service application in Tucson, Arizona.

In
April

2011 Zhuang Wang and Cungang Yang presented a paper on secure routing

for wireless mesh networks. This paper describes

a S
ecurity Enhanced AODV rout
ing


Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25


protocol for wireless mesh networks (SEAODV).SEAODV employs Blom’s key pre
-
distribution scheme to compute the pair
-
wise transient key (PTK) through the flooding
of enhanced HELLO message and subsequently uses the establ
ished PTK to distribute

the group transient key (GTK). PTK and GTK are used for authenticating

U
ni
-
cast and
broadcast routing messages respectively. In wireless mesh networks, a unique PTK is

shared by each pair of nodes, while GTK is shared secretly bet
ween the node and all
its one
-
hop neighbours. A message authen
tication code (MAC) is attached as the
extension to the original AODV routi
ng message to guarantee the mes
sage’s
authenticity and integrity in a hop
-
by
-
hop fashion.


Security analysis and perfor
mance evaluation show that SEAODV is more effectiv
e in
preventing identified rout
ing attacks and outperforms ARAN and SAODV in terms of
computation cost and route acquisition latency.


Apart from these a number of researches are still being carried out to
address the
issues still remaining in WMNs .












Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25


2.2
Case study on Wireless Mesh Networks:



A Survey

Wireless mesh
networks is

a most typical application of mesh
architectures.

As various
wireless networks evolve into the next gener
ation to provide better services, a key
technology, wireless mesh networks has emerged recently.

Wireless

mesh was
originally developed
for military

applications but has
undergone significant

evolution in
the past
decade. As

the cost of the radios plummete
d, single radio products evolved to
support more radios per mesh node with the additional radios providing specific
functions
-
such as client access, backhaul service or scanning radios for high speed
handover in

mobility applications. The mesh node design
also became modular
-
a single
box could support multiple radio cards
-
each operating at a high frequency.


A wireless mesh network is a communications network made of radio nodes organised
on a mesh topology. The coverage area of the radio nodes working
as

a

single network
is sometimes called a cloud. Access to this mesh cloud is dependent on the radio nodes
working in harmony with each other to create a radio network. A mesh network is
reliable and offers redundancy. When one node can no longer operate, the
rest of the
nodes can still communicate with each other, directly or through one or more
intermediate nodes.


A wireless mesh network can be seen as a type of wireless adhoc
network, where all the nodes are static and doesn’t experience direct mobility.

In

WMNs, nodes are comprised of mesh routers and mesh
clients. Each

node operates

not only as a
host but also as a router forwarding packets on behalf of other nodes that
may not be within the direct transmission range of their destinations.

A

WMN

is dynami
cally
self
-
organised and self
-
configured, with the nodes in the
network automatically establishing and maintaining mesh connectivity among
themselves. This feature brings many advantages to WMNs such as low upfront cost,
easy network maintenance, robustnes
s, and reliable service coverage.

Conventional
nodes equipped with network interface cards (NICs) can directly communicate to the
wireless mesh networks. Customers
without wireless NIC

can communicate with mesh
network by connecting to wireless mesh
router
s, for

e.g., through
Ethernet. Thus, WMN
will greatly help people to be online anywhere anytime. Moreover, the gateway and
bridging functionalities of mesh routers enable the integration of WMNs with various
existing networks such as cellular, wireless sen
sor, wireless
-
fidelity

[
114
]
, world
-
wide
interoperability for microwave access
[
117
], Wi

media

[118
]

networks.


Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25


WMN is a promising technology for numerous applications

[77
]
, e.g. Broadband home
networking, community and neighbourhood networking, enterprise

networking,
building automation, etc.it is gaining significant attention as a possible way for the cash
strapped Internet service providers(ISPs),carriers, and others to roll out to robust and
reliable wireless broadband service access in a way that needs

minimal upfront
investments. With the capability of self
-
organisation and self
-
configuration, WMNs can
be deployed incrementally one node at a time as needed.as more and more nodes are
installed, the reliability and connectivity for users increase accordi
ngly.

Deploying a WMN is not too difficult since all the required components are already
present in form of adhoc network routing protocols, IEEE 802.11 MAC protocol, etc.
Several companies have already realised the potential of this technology and offer
w
ireless mesh networking products. However, to make WMN be it all can be
considerable research efforts are still needed. For example, the available MAC and
routing protocols applied to WMNs do not have enough scalability: the throughput
drops significantly
as the number of nodes or hops in a network increases. Similar
problems exist in other networking protocols. Consequently, all existing protocols from
the application layer to transport, network MAC, physical layers need to be enhanced or
re
-
invented.





2.2.1
NETWORK ARCHITECTURE

Wireless mesh architecture is quite different from a cellular or wireless LAN
architecture. All nodes are equal so there is no centralized control and, therefore, each
node must participate in networking as well as be
a source or sink of traffic. Rather than
a single hop to a base, multi
-
hopping amongst nodes is a common capability. All this
brings the promise of great flexibility, particularly when we wish to create a new
network, or expand an existing one.

Wireless me
sh architecture is a first step towards providing high bandwidth network
over a specific coverage area. Wireless mesh architecture’s infrastructure is, in effect, a
router network minus the cabling between nodes. It’s built of peer radio devices that
don’t

have to be cabled to a wired port like traditional WLAN access points (AP) do.
Mesh architecture maintains the signal strength by breaking the long distances into a
series of shorter hops. Intermediate nodes not only boost the signal, but cooperatively
ma
ke forwarding decisions based on their knowledge of the network, i.e. performing
routing.

Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25


WMNs consist of two types of nodes: mesh routers and mesh
clients. Other

than the
routing capability for gateway repeater functions as in a conventional router, a wi
reless
mesh router contains additional routing functions to support mesh networking. To
further improve the flexibility of mesh networking, a mesh router is usually equipped

with

multiple wireless interfaces built on either the same or different wireless a
ccess
technologies. Compared

with a conventional wireless router, a wireless mesh router can
achieve the same coverage with much lower transmission power through multi
-
hop
communications. Optionally MAC: medium

access control

protocol in a mesh router is
e
nhanced with better scalability in a multi
-
hop mesh environment.


In spite all these differences, mesh and conventional wireless routers are usually built
based on a similar hardware platform. Mesh routers can be built based on dedicated
computer systems (
embedded systems) and look compact. They can also be built on
general
-
purpose computer systems (e.g., laptop, desktop PC).

Mesh clients also have necessary functions for mesh networking, and thus, can also
work as a
router. However
, gateway or bridge funct
ions do not exist in these nodes.

I
n
addition mesh clients usually have only one wireless
interface. As

a consequence, the
hardware platform and the software for mesh clients can be much simpler than those for
mesh routers. Mesh clients can have a higher v
ariety of devices compared to mesh
routers. They can be laptop, desktop PC, pocket PC, PDA, IP phone and many other
devices.

Many researchers have worked on
proposing various architectures

that are
related to
improving coverage and data rates i
n wireless n
etworks

[
91
]
[
54
]
.

The architecture of WMNs can be classified into three main groups based on the
functionality of nodes:

ACCESS
/BACKBONE NETWORK:


It is a

mesh with hierarchy of node types that supports both intra

as well as extra mesh
traffic. I
n other
words, the overlay

routing network also has gateways to other, external
networks such as internet.
This type of WMNs includes mesh routers forming an
infrastructure for the clients that connect to them.
The mesh routers form a mesh of self
-
configuring,

sel
f
-

healing links among themselves. With gateway functions, mesh
routers can be connected to the
internet. This approach
, also referred to as infrastructure
meshing provides backbone for conventional clients and enables integration of WMNs
with existing wir
eless networks, through gateway/bridge functionalities

in mesh
routers.
Conventional

clients with Ethernet interface can be connected to mesh routers

via
Ethernet
links. For

conventional clients with the same radio technologies as mesh
routers, they can di
rectly communicate with the mesh routers. If different radio
technologies are used, clients must communicate with the base stations that have

Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25


Ethernet connections to mesh routers.

Access
/ backbone WMNs are the most
commonly used type. For example, commun
ity and neighbourhood networks can be
built using infrastructure meshing. The mesh routers are placed on the roof tops of
houses in a neighbourhood, which serve as access points for users inside the homes and
along the roads. Typically two types of radios
are used in the routers, i.e. for backbone
communication and for user communication, respectively. The mesh backbone
communication can be established using long range communication techniques such as
directional antennas.




Fig.6 Access/Backbone archi
tecture

(
I.F. Akyildiz et al. / Computer Networks 47 (2005)
)


Client/Pure WMNs:


All traffic in a pure mesh is intra
-
mesh, i.e. the mesh is isolated. Client meshing
provides peer
-
to peer networks among client devices. In this type of architect
ure; client
nodes constitute the actual network to perform routing and configuration functionalities
as well as providing end
-
user applications to customers. Hence, a mesh router is not
required for these types of
networks. In

Client WMNs a packet destined

to a node in the
network hops through multiple nodes to reach the destination. Client WMNs are usually
formed using one type of radios on devices. Moreover, the requirements on end
-

user
devices is increased when compared to infrastructure meshing, since
, in client WMNs,
the end
-
users must perform additional functions such routing and self
-
configuration.

Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25


Fig.7 Client Architecture



(
I.F. Akyildiz et al. / Computer Networks 47 (2005)
)


Hybrid WMNs:

This architecture is the combination of infrastructu
re and client meshing .Mesh clients
can access the network through, mesh routers as well as directly meshing with other
mesh clients. While the infrastructure provides connectivity to other networks such as
internet, WIFI, Wi MAX, cellular, and sensor netw
orks: the routing capabilities provide
improved connectivity and coverage inside the WMN.



Fig.8

Hybrid architecture



(
I.F. Akyildiz et al. / Computer Networks 47 (2005)
)


Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25


2
.
2.
3
CHARACTERISTICS


Multihop wireless networks:


An objective to dev
elop WMNs is to extend the coverage range of current wireless
networks without sacrificing the channel capacity. Another objective is to provide non
-
line
-
of
-
sight (NLOS
) connectivity among the users without direct line
-
of
-
sight (LOS)
links. To meet these r
equirements, the mesh style mul
ti
-
hopping
is indispensable

[120
]
,
which achieves higher throughput without sacrificing effective radio range via shorter
link distances, less interference between the nodes, and more efficient frequency re
-
use.

Support for
adhoc

-
networking,

and capability
of self
-
forming, self
-
healing, self
-
organization:

WMNs enhance network
performance,

because of flexible network architecture
, easy
deployment and configuration, fault
-
tolerance, and mesh
-
connectivity, i.e., multipoint
-
to
-
m
ultipoint communications

[106
]
. Due to these features, WMNs have low upfront
investment requirement, and the network can grow gradually as needed.

Mobility dependence on the type of mesh nodes
:

M
esh routers usually have minimal mobility, mesh
-

clients can
be stationary or mobile
nodes.

Multiple types of network access:


In WMNs, both backhaul access to the internet and peer
-
to
-
peer (P2P) communications
are supported

[59
]
. In addition, the integration of WMNs with other wireless networks
and providing servic
es to end
-
users of these networks can be accomplished through
WMNs.

Dependence of power
-

consumption constraints on the type of
mesh nodes:

M
esh routers usually do not have strict constraints on power
consumption. However,
mesh clients may require power ef
ficient protocols. As an example, mesh
-
capable
sensor requires its communication protocols to be power efficient. Thus, the MAC or
routing protocols optimized for mesh routers may not be appropriate for mesh clients
such as sensors, because power efficienc
y is the primary concern for wireless sensor
networks

[48
]
.

Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25


Compatibility and interoperability with existing wireless
networks:

For example, WMNs built based on IEEE 802.11
technologies.
It m
ust
be
compatible
with

IEEE 802.11 standard
in the sense of
supp
orting both

mesh
-
capable and
conventional Wi
-
Fi clients. Such WMNs need to be interoperable with other wireless
networks such as Wi
-
MAX
, Zig
-
Bee

[
124
]
, and cellular networks.


2
.
2.
4

Application scenarios

Research and development of WMNs is motivated
by sev
eral applications which clearly
demonstrate the promising market while at the same time these applications cannot be
supported directly by other wireless networks such as cellular networks, adhoc
networks, wireless sensor networks, standard IEEE 802.11.

Br
oadband home networking:

Currently broadband home networking is
realized through IEEE 802.11WLA
Ns.an obvious problem is that o
f

the access
points.
Without

a site
survey, a

home (
even a small one) usually has many dead zones without
service coverage.

Soluti
ons

based on site survey are expensive and not practical for
home
networking, while

installation of multiple access points is also expensive and not
convenient because of Ethernet wiring for access points to backhaul network access
modem.

Moreover communi
cations between
end
nodes under two

different

access points have to
go all
the way back to the access
hub. This

is obviously not an efficient solution,
especially for broadband
networking. Mesh

networking can resolve all these issues in
home networking.

Th
e access points must be replaced by wireless mesh routers with mesh connectivity
established among them. Therefore, the communication between these nodes becomes
much more flexible and more robust to network faults and link failures. Dead zones can
be elim
inated by adding mesh routers, changing locations of mesh routers, or
automatically adjusting power levels of mesh routers. Communication within home
networks can be realized through mesh networking without going back to the access
hub all the time. Thus,
network congestion due to backhaul access can be
avoided. In

this application, wireless mesh routers have no constraints on power consumption and
mobility. Thus, protocols proposed for mobile adhoc networks and wireless sensor

Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25


networks are too cumbersome

to achieve satisfactory performance in this application.
On the other hand, Wi
-
Fi’s are not capable of supporting adhoc
-

Multihop networking.




Fig.
9

WMNs for Broadband Home Networking


(
I.F. Akyildiz et al. / Computer Networks 47 (2005)
)

Community and neighbourhood
networking:


I
n

a community the common architecture for netwo
rk access is based on cable or DSL

connected to the
internet, and

the last hop is wireless by connecting a wireless router to
a cable or DSL
modem. This

type of netw
o
rk access has several drawbacks:

(1)Even if the information must be shared within a community or neighbourhood, all
traffic must flow through internet. This significantly reduces network resource
utilization.

(2) Large percentage of areas in between house
s is not covered by wireless services.

(3
) An

expensive but high band
-
width gateway between multiple homes and neighbours
may not be shared and wireless services must be set up individually.
as a result network
service costs may increase.

(4
) Only

a single
path may be available for one home to access the internet or
communicate with neighbours.

Literat
ure survey on Wireless Mesh Networks


Asma Rafiq,

P. G .Department of Computer Sciences


25


WMNs mitigate the above disad
vantages through flexible mesh connectivity

between
homes.

WMNs can also enable many applications such as distributed file
storage,
dist
ributed

file access, and video streaming.



Fig.10

WMNs for Community neighbourhood networking

(
I.F. Akyildiz et al. / Computer Networks 47 (2005)
)

Enterprise
networking
:

T
his

can be a small network within an office or a medium sized network for all of
fices
in an entire
building, or

a large scale network among offices in multiple
buildings.
Currently
, IEEE

802.11 networks are used widely in various
offices. However

these
networks are still isolated
islands. Connections

among them have to be achiev
ed
thr
ough Ethernet connections
, which is a key reason for the high cost of
enterprise
networks.in addition adding more backhaul access modems only increases capacity
locally, but does not improve robustness to link failures, network congestion and other
problem
s of the entire enterprise
network. If

the access points are replaced by mesh