21nodes_Rural Mesh_VoIP Project

8/11/2019 21nodes_Rural Mesh_VoIP Project

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Designing of a Rural Wireless Mesh Network of 21 Nodes

Final Assignment (Optional)

WIRELESS COMMUNICATIONS [MTEL] [A]

Corse Teacher: SHARMIN, AFSAH

Submitted By:

Fuad, Kazi Ahmed Asif

ID: 14-97541-1

Masters in EEE

American International University-Bangladesh(AIUB)


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Wireless Mesh Network:

Wireless Mesh Network (WMN) Multi-hop peer-to-peer wireless network in which nodes connect with

redundant interconnections and cooperate with one another to route packets .Wireless Mesh Network

(WMN) relies on all the nodes to propagate signals. The term 'wireless mesh networks' describes wireless

networks in which each node can communicate directly with one or more peer nodes. The term 'mesh'

originally used to suggest that all nodes were connected to all other nodes, but most modern meshes

connect only a sub-set of nodes to each other. The nodes are able to configure automatically and re-

configure dynamically to maintain the mesh connectivity. This gives the mesh its self-forming and self-

healing characteristics. Still, this is quite different than traditional wireless networks, which require

centralized access points to mediate the wireless connection. Although the wireless signal may start at

some base station (access point) attached to a wired network, a wireless mesh network extends the

transmission distance by relaying the signal from one computer to another. WMN provides Wi-Fi

connectivity within an urban or suburban environment. It comprises "mesh routers/nodes" which are a

combination of base station (access point) and router in one device. 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 direct wireless transmission range of their destinations. A

WMN is dynamically self-organized and self-configured, with the nodes in the network automaticallyestablishing and maintaining mesh connectivity among themselves.

Extend the range and link robustness of existing Wi-Fis by allowing mesh-style multi-hopping. A user

finds a nearby user and hops through it - or possibly multiple users - to get to the destination. Every user

becomes a relay point or router for network traffic. Mesh networks consist of multiple wireless devices

equipped with COTS802.11 a/b/g cards that work in ad-hoc fashion. 802.11 capable antennas placed on

rooftops allow large area coverage.

Figure 1: A simple WMN.

In short: WMN is Multi-hop network built from wireless routers.

Wireless Mesh Node & Access Point

Both wireless mesh node & access point consist of a wireless router and an antenna. These could be

installed indoors or in a weather-proof enclosure outdoors. The antenna could be the standard indoor

omnidirectional antenna or it could be an externally mounted omnidirectional or directional antenna. A

mesh node communicates only with other wireless mesh nodes. On the other hand wireless access point

creates a hotspot where any Wi-Fi enabled device can connect to the wireless access point.


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Mesh Networking

Network Topologies: In Full mesh each node is directly connected to all other nodes on the other hand Partial mesh not all

nodes are directly interconnected. Figure 2 shows different types of mesh networking.

Figure 2: Types of Mesh Networking/

Characteristics of a WMN:

WMNs are considered to be a subclass of ad hocnetworking--> Routing nodes are stationary (unlike in Mobile Ad Hoc Networks,MANETs)

WMNs have properties of an autonomic system:- Self-Configuration- Self-Healing (redundant, decentralized, no central point of failure)- Self-Management- Self-Optimization--> Challenging tasks for a good system design

High overall capacity:- Spatial diversity- Power management

Important constraints:- Shared bandwidth & interference- Number and location of nodes

Network Architecture

WMNs consist of two types of nodes: Mesh Routers and Mesh Clients

Mesh router

Additional routing functions to support mesh networking. Multiple wireless interfaces with same or

different wireless access technologies. The gateway/bridge functionalities enable the integration of WMNs

with existing wireless networks (cellular, sensor-net, Wi-Fi, WiMAX).

Mesh Clients

Conventional nodes (e.g., desktops, laptops, PDAs, Pocket-PCs, phones, etc.) equipped with wireless

network interface cards (NICs), and can connect directly to wireless mesh routers. Customers without

wireless NICs can access WMNs by connecting to wireless mesh routers through, e.g., Ethernet.

Figure 3 shows the examples of mesh routers based on different embedded systems: (a) PowerPC and

(b) Advanced RISC Machines (ARM).

Figure 4 shows the examples of mesh clients: (a) Laptop, (b) PDA, (c) Wi-Fi IP Phone and (d) Wi-Fi RFID

Reader.


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Figure 3: WMN Routers

Figure 4: WMN Clients

WMN Architecture Classifications

Infrastructure Meshing

Client Mesh Networking

Hybrid Mesh Networking

Infrastructure Meshing

Mesh routers form a mesh infrastructure among themselves.

Provides backbone for clients and enables integration of WMNs with existing wireless networks

and Internet through gateway/bridge functionalities.

Clients connect to mesh router with wireless link or Ethernet

Figure 5 Shows Infrastructure Meshing

Client WMNs

Client nodes constitute peer-to-peer network, and perform routing and configuration

functionalities as well as provide end-user applications to customers, mesh routers are not

required.


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Multi-hop routing.

Client nodes have to perform additional functions such as routing and self-configuration.

Figure 5:

Figure 6

Hybrid WMNs

A combination of infrastructure and client meshing.

Infrastructure provides connectivity to other networks such as the Internet, Wi-Fi, WiMAX,cellular, and sensor networks;

Mesh clients can access the network through mesh routers as well as directly meshing with other

mesh clients.

The routing capabilities of clients provide better connectivity and coverage


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Figure 7

Important Network Management Protocols

Mobility Management

Distributed scheme for WMNs can besimpler because the existence of backbonenodes.

Take advantages of the network backboneto design a light-weight distributed mobilitymanagement scheme for WMNs.

Location service is a desired feature byWMNs.

Power Management

For mesh routers, power managementaims to control connectivity, interference,spectrum spatial-reuse, and topology.

For mesh clients, protocols should bepower efficient.

Network Monitoring

Report statistics in the MIB to one or several servers.

Data processing algorithms analyze these statistical data and determine potential abnormality. To reduce overhead, schemes for efficient transmission of network monitoring information are

expected.

To accurately detect abnormal operation and quickly derive network topology of WMNs, effectivedata processing algorithms need to be developed.

Security

WMNs lack efficient and scalable security solutions

Distributed network architecture

Vulnerability of channels and nodes in the shared wireless medium

Dynamic change of network topology.

Two strategies

Embedding security mechanism into network protocols

Developing security monitoring response systems


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How to design and implement a practical security system, including cross-layer secure network

protocols and various intrusion detection algorithms, is a challenging research topic.

WMNs Standards

WPAN: Bluetooth, Zigbee

WiFi: 802.11a, b, g, n

WiMAX: 802.16

Figure 8: Data rates of different Standards.

Wireless Mesh Networking Principles

Communication between mesh nodes are based on Wi-Fi radios (IEEE 802.11 a/b/g) attached to

directional or Omni-directional antennas.

All radios are set to ad-hoc mode (not client mode or infrastructure (access point) mode).

Each node in the WMN has the same ESSID (name) and BSSID (number) - the BSSID should be

fixed to prevent partitioning of the wireless network.

All nodes in the WMN will operate on the same channel (frequency).

In an ideal WMN, each node should be able to see at least two other nodes in the WMN.

This allows full fail-over in case any node goes out of commission (e.g. due to a hardware failure

or power failure).

A mesh routing protocol, like OLSR, will route IP traffic between the wireless interfaces of the

mesh nodes. It learns the potential routes by listening to the routing information exchanged in the

network and maintains routing tables dynamically. This feature provides routing fault-tolerance by

providing an alternative route when a node fails, if one is available.

No non-mesh wireless device connects directly to a wireless mesh node (mesh nodes provide awireless back-bone). This infrastructure is considered critical infrastructure and should be

managed for the highest availability as the rest of the network depends on the availability of each

node. The login on the mesh nodes should only be available to the technical team and not to all

users of the mesh network.

Each IP address in the mesh network should be unique to allow any computer in the network to

connect to any other computer in the network.


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A computer can connect to the mesh network via LAN cables connected to the mesh node or via

a wireless connection to a separate access point (hotspot) connected to the LAN side of a mesh

node.

One or more mesh nodes may be connected to a specially prepared node linking into a distant

network. This node may also be a mesh node, but will not be configured the same as the local

mesh nodes.

Advantages of Wireless Mesh Networking

Price: 802.11 radios have become quite cheap, but the radios are often still amongthe most expensive elements of such a network. The fact that each meshnode runs both as a client and as a repeater potentially means saving on thenumber of radios needed and thus the total budget.

Ease and simplicity: If you have a box that is pre-installed with wireless mesh software and usesstandard wireless protocols such as 802.11b/g, the setup is extremelysimple. Since routes are configured dynamically, it is often enough to simplydrop the box into the network, and attach whatever antennas are required forit to reach one or more existing neighboring nodes (assuming that we cansolve the issue of IP address allocation).

Self-forming & Self-healing

The wireless mesh network forms automatically once the mesh nodes havebeen configured and activated. Once restored, a node rejoins the meshnetwork seamlessly.

Organization andbusiness models

The decentralized nature of mesh networks lends itself well to adecentralized ownership model wherein each participant in the network ownsand maintains their own hardware, which can greatly simplify the financialand community aspects of the system.

Network robustness The character of mesh topology and ad-hoc routing promises greater stabilityin the face of changing conditions or failure at single nodes, which will quitelikely be under rough and experimental conditions.

Power The substrate nodes of a mesh network can be built with extremely lowpower requirements, meaning that they can be deployed as completelyautonomous units with solar, wind, or hydro power.

Power generating units are typically connected to points of infrastructureand human presence. This makes them valid locations for network nodes. Asa secondary benefit, the presence of integrated network nodes within powernetworks may allow for better monitoring and management.

Integration Mesh hardware is typically small, noiseless, and easily encapsulated inweatherproof boxes. This means it also integrates nicely outdoors as well asin human housing.

Reality fit Reality rarely comes as a star, ring, or a straight line. In difficult terrain -- bethat urban or remote -- where not every user can see one or few centralpoints, chances are one can see one or more neighboring users.

Ease of deployment With little training members of a community can build their own nodes,configure and deploy them in the community.

Drawbacks

Radio is a shared medium and forces everyone to stay silent while one person holds the stage. Wired

networks, on the other hand, can and do hold multiple simultaneous conversations. In a single radio ad

hoc mesh network, the best you can do is (1/2)nat each hop. So in a multi hop mesh network, the max

available bandwidth available to you degrades at the rate of 1/2, 1/4, 1/8. By the time you are 4 hops

away the max you can get is 1/16 of the total available bandwidth. That does not sound too bad when you

are putting together a wireless sensor network with limited bandwidth and latency considerations. It is


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DISASTROUS if you wish to provide the level of latency/throughput people are accustomed to with their

wired networks. Consider the case of just 10 client stations at each node of a 4 hop mesh network. The

clients at the last rung will receive -at best- 1/(16,0000) of the total bandwidth at the root.

IEEE 802.11: Wi-Fi

Wi-Fi is defined as any "wireless local area network (WLAN) products that are based on the IEEE 802.11standards. Popular technology that allows an electronic device to exchange data wirelessly (using radio

waves) over a computer network. IEEE established the 802.11 Group in 1990. Specifications for standard

ratified in 1997. Initial speeds were 1 and 2 Mbps. IEEE modified the standard in 1999 to include 802.11a

(54 Mbps) and 802.11b (11 Mbps). Incidentally, 802.11b equipment was available before 802.11a.

802.11g (54 Mbps) was added in 2003. In many respects, the IEEE 802.11b wireless LAN (WLAN)

standard is similar to that of classic IEEE 802.3 (Ethernet) LANs.

Wi-Fi Features

Infrastructure mode vs ad hoc mode:

Devices in a wireless network are set up to either communicate indirectly through a

central place an access point or directly, one to the other.

Access Point (AP) sends beacon frames all the information about the network (e.g.

Timestamp Capability information)

Mobiles choose AP based on signal strength

Multiple channel access protocols supported

CSMA/CA (DCFDistributed coordination function); PCF (Point Coordination Function);

RTS/CTS (Request to Send/Clear to Send)

MAC-layer can provide error control, retransmission, rate adaptation, etc.

Direct Sequence Spread Spectrum (DSSS)

Modulation technique

Signal spread across 22 MHz with each channel based around a center frequency. There

are fourteen 22-MHz channels.


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Medium Access Control (MAC)

Carrier Sense Multiple Access with Collision Avoidance (CSMA-CA)

Device wanting to transmit senses the medium (air)

If medium is busy, it defers

If medium is free for certain period (DIFS Distributed Inter-Frame Space), it transmits

frame

DIFS is approximately 128 s

Latency can increase if air is very busy since devices will have a hard time finding open

air to send frames!

DIFSDistributed Inter-Frame Space (approx. 128 s)

SIFSShort Inter-Frame Space (approx. 28 s)

Every frame is ACKed except broadcast/multicast

If no ACK received right away, then the sender retransmits the frame again at the MAC

layer

indicates frame (or ACK) was lost/corrupted

very short timeout (e.g., 1 ms)

exponential back off (doubling) if repeated loss

Typically recovers before TCP would notice

Max retransmission limit (e.g., 8)

May do MAC-layer rate adaptation or frame fragmentation if channel error rate is high

Other Wi-Fi Features:Power Management

Mobile nodes can sleep to save

power

Accomplished by using DTIM

(Delivery Traffic Indication Message)

Security

Wired Equivalent Privacy (WEP)

Not very secure at all!

To address this weakness, there is WPA2 (IEEE

802.11i)


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intervals

AP will buffer frames until client

requests them

AP can use virtual bitmap field in

beacons to indicate which stationshave data waiting.

Uses CCMP, an AES-based encryption mode

with strong security

What is a Softswitch?

A soft switch is a centrally located device within a telephone network that is used to link calls from one telephone line to the

other, through the use of specialized software. The functions of the softswitch were earlier undertaken by hardware, with

physical switches being used for the routing of calls. In short, the basic function of the soft switch is to separate the

hardware and software of a circuit switched network.

Soft Switch Architecture

Wireline & wireless industry see the softswitch architecture as a key component in the next generation telecommunication

network. In fact, several operators and vendors see the advent of the softswitch architecture as pivotal for continued cost

efficiency and revenue growth.The term softswitch was coined by one of the founders of the Softswitch Consortium, Ike

Elliott, in the late nineties. Although frequently used, the term is quite elusive. In fact, to our knowledge, there exists no

precise definition of the term. The principal idea behind the softswitch architecture is to separate the control and media

functions of a traditional telecom switch. In particular, as illustrated in Figure 19, the softswitch architecture prescribes a

separation and/or distribution of the application, call control, and media transport functions of legacy telecom switches.

That is, the architecture decouples the underlying switching hardware from the control, service, and application functions.

Figure 20 illustrates the distributed architecture that is generally agreed upon as the softswitch architecture. The archi-

tecture is bearer independent, and could be applied to both packet- and circuit-switched networks. However, given that the

next-generation telecommunication networks are assumed to be packet switched, the softswitch architecture is almost

exclusively applied to packet-switched networks. In fact, in the contexts used, it is often tacitly assumed that the underlying

network is either IP-based or based on Asynchronous Transfer Mode.

Figure 1: The Principal idea behind the softswitch.

As follows from Figure 2, the principal components of the softswitch architecture are softswitch, Media Gateway (MG),

Signaling Gateway (SG), and Feature/Application Server (AS). The softswitch constitutes the intelligence that coordinates

all signaling such as call-control signaling, operations and management signaling, and bearer signaling. The name


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softswitch originates from the fact that the majority of signalingfunctionality in a softswitch resides in software as

compared to hardware in traditional telecom switches.

Figure 2: Softswitch architecture components.

Figure 3: Primary function of Softswitch


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How does it work?

There are different components in the system that manages the different functions. The Softswitch is controlled by the Call

Agent. This is a sort of administrator that regulates applications such as services, billing, signaling and routing of calls. The

Call Agent has the capacity to monitor a number of Media Gateways over areas that are separated by considerable

distance. This has become possible through the use of a Transmission Control Protocol/Internet Protocol or TCP/IP

connection. The Media Gateway functions by linking different kinds of media streams to set up an end-to-end pathway for

the voice and data transmission in the call. It may be equipped with a number of interfaces of different kinds, allowing for

connection to different kinds of networks conventional Public Switched Telephone Network or PSTN systems involving

DS1 or DS3 (Digital Signal) ports. On the other hand, it may be equipped to accommodate interfaces linking up to ATM

(Asynchronous Transfer Mode) or IP systems. Modern systems will also accommodate Ethernet interfaces for VoIP

applications. The Call Agent directs the media gateway to link media streams between the interfaces, making it possible to

connect the call. The Media Gateway may also be linked to any number of accessing gadgets. These could be analog

telephone adaptors or ATAs (Analog Telephone Adaptor) with a single RJ (Registered Jack) 11 socket for the telephone

jack; the Media Gateway could also be connected to a PBX (Private Branch Exchange)or an Integrated Access Device

(IAD), which has the capacity to accommodate hundreds of telephone connections. Normally the larger access devices are

housed in buildings in close proximity to the clients for whom they are intended. All it takes is a pair of copper wires to link

the end user to the IAD. PBXs and devices of medium size would be suitable for use on commercial properties. Single line

devices would be more suitable for residential premises.

Figure 4: Process of Softswitch


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Advantages of VSATs

If by now you believe that VSATs provide an edge over terrestrial lines only in cases where the land linesare difficult to install, say in the case of remote locations, then consider this. Close to 50 percent of thetotal VSAT population is installed in the US which also boasts of world's best terrestrial communications.

Networking of business activities, processes and divisions is essential to gain a competitive edge in anyindustry. VSATs are an ideal option for networking because they enable Enterprise Wide Networking withhigh reliability and a wide reach which extends even to remote sites.

Access Technologies

The primary objective and advantage of these networks is to maximise the use of common satellite and

other resources amongst all VSAT sites. The method by which these networks optimise the use of

satellite capacity, and spectrum utilisation in a flexible and cost effective manner are referred to as

satellite access schemes. Each of the above topologies is associated with an appropriate satellite access

scheme. The most commonly used satellite access schemes are:

Time Division Multiple Access(TDMA)

Frequency Division Multiple Access(FDMA)

Code Division Multiple Access(CDMA)

Demand Assigned Multiple Access(DAMA)

Pre-Assigned Multiple Access(PAMA)

Frequency-Time Division Multiple Access(FTDMA)

Advantages of Satellite Communication

The advantages of satellite communication over terrestrial communication are:

The coverage area of a satellite greatly exceeds that of a terrestrial system.

Transmission cost of a satellite is independent of the distance from the center of the coverage

area.

Satellite to Satellite communication is very precise.

Higher Bandwidths are available for use.


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Important FactsRF Communications BasicsTransmission Formula (ideal conditions) Friis transmission formula (free space, ideal isotropic antennas):

[1]

Pr: Signal power available at receiver antenna output [W]Pt: Signal power fed to transmitter antenna input [W]d: Distance between antennas [m]f: Frequency [Hz]c: Speed of light (3 x 108 m/s)

Where Does Wireless RF Live?ISM (Industrial, Scientific, Medical) Band

Multipath Fading and Shadowing

Multipath fading: diffraction, reflection, scattering Shadowing: absorption

Transmissions under Non-ideal ConditionsEffects to consider Distance between transmitter and receiver (Friis transmission law): Path loss Receiver sensitivity: Thermal noise Multipath fading: Reflection (eg. ground, buildings, water surface), diffraction, refraction

Shadowing: Absorption (e.g. walls, buildings, rain, windows) Interference: same source or different source- May annihilate signal (same frequency & amplitude, 180o fixed phase relation)- May amplify signal (same frequency, 0o fixed phase relation)


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- May be caused by other radio sources (e.g. microwave oven, WLAN, WPAN)

Technical: Antenna Gains, Cable Losses

Communication Range CalculationsUse of the Decibel (dB)Ratio between two quantities expressed by a dimensionless logarithmic unit [dB] May be used in different application areas (acoustics, physics, electronics) Usage in calculations for RF communications:Ratio between two power values = 10 log10(P2/P1) Special use: [dBm] = Power level relative to a reference value of 1 mWExamples:- Typical 802.11 receiver sensitivity -60...-80 dBm

- Typical 802.11 maximum transmitter power ~14 dBm- Typical minimal Signal-to-Noise (S/N, SNR) values for BPSK modulation ~6 dB Special use: [dBi] = Antenna gain relative to an isotropic antenna (one-point source)Examples: 2 dBi (simple antenna), 5 dBi (omnidirectional), 18-27 dBi (parabolic)

Communication Range CalculationsStrength of received signalReceive signal strength expressed in dBm (non isotropic antennas):

Pr: Signal power available at receiver antenna outputPt: Signal power fed to transmitter antenna input

Lfs: Free space lossGt, Gr: Gain of transmit antenna, of receive antenna

Path loss (free space)

d: Distance between antennasf: Frequencyc: Speed of light

Communication Range Calculations Maximum usable communication range is given by:- Signal strength at receiver- Noise level at receiver- Minimum required S/N (given by modulation and coding used) Signal-to-Noise Ratio (SNR):

Thermal noise level:


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kB: Boltzmanns constant [J/K]T: Temperature [K]fbw: Bandwidth [Hz] Formula for room temperature (20o C equiv. 293 K) for a non-ideal receiver:

NF (Noise Figure): Ratio of actual receiver noise to ideal receiver noise

Antenna Types Many different forms:- omnidirectional radiation pattern- sectorial radiation pattern- directive radiation patternsAntenna: reciprocity property (same behavior for transmit/receive) Basic reference is ideal isotropic antenna (radiates equally in all directions)Antenna gain: expressed in dBi relative to an ideal isotropic antenna Example Cantenna:- Uses a tin can as a wave guide

- Cheap solution for developing countries

MIMO (Multiple-Input Multiple-Output) Antennas

MIMO is a promising multi-antenna systems approach to:- increase link capacity (eg. 802.11n)- improve robustness- benefit from constructive interference- avoid destructive interference

MIMO allows for:- multiple radio links (spatial multiplexing)- space-time coding

Routing in Wireless Mesh NetworksDifferences to Wired Networks Topology changes related to environmental fluctuations- new nodes may join- nodes may leave network- link qualities may vary over time (movement)--> Dynamics may prevent convergence of routing algorithm Limited bandwidth and battery life--> periodic updates are unattractive

Partly unidirectional links--> computed routes may not work Many redundant links--> increase routing updatesAdditional factors to consider for path selection- link quality (stability, BER, bandwidth, ...)- interference

IMPORTANT CONSIDERATIONS


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Cost of planning versus the cost of supportThere is a trade-off between the cost of planning and building of a network well at the start of the projectand the cost of maintaining a badly designed network. It is worth the effort to plan thoroughly, get theappropriate equipment and to create redundant routes in the wireless mesh network wherever possible.

Telecommunications Regulations

Each country has a regulatory body that regulates the use of wireless equipment. Check with your localregulator for any specific regulations regarding Wi-Fi equipment, the use of the 2.4 GHz and 5.8 GHzbands, and maximum power output for wireless equipment.

Wireless network planning (channels)The only three non-overlapping (non-interring) bands in the IEEE 802.11 b/g standards and they arechannels 1, 6, and 11.

Ethernet network planning (subnets)IP4 addresses are assumed but IPv6 is also possible. This document will not deal with IPv6.

Wi-Fi is a line-of-sight technologyVarious obstructions may interfere with the signals and should be considered:

- Trees and plantswater on leaves negatively impact on signal strength

- Construction materialsmetal objects like roofs or reinforcing in concrete walls affect the signalstrength.

Sources of interferenceMicrowave ovens, air-conditioners and other radio equipment could interfere with Wi-Fi equipment. It isbest to avoid interference in order to secure a good link.

LightningElectronics are susceptible to lightning damage and lightning protection should be considered, especiallyfor outdoor installations of Wi-Fi equipment.


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PLANNING THE WIRELESS MESH NETWORK

Planning should be done carefully otherwise when the network starts to grow it becomes a night mare. The following stepsmight help.

Creating the Map

> Identify and plot the sites (houses/offices) that will receive a mesh node (Linksys): Usually one would get the GPScoordinates of these sites in order to plot them on Google Earth. The GPS coordinates can also be used when doing radioplanning with specialized tools which can give a digital terrain elevation model of each link. As a minimum requirementone should have at least a schematic plot of the sites. The position of each node does not need to be very accurate,although the position of nodes relative to each other is helpful when assigning channels and IP addresses.>Plan the wireless mesh network (radio links): The sites can now be linked together using the plot. Each link is defined asthe straight line between two wireless nodes. The length of each link should reflect the distance between the sites. Manypossible links exist with a mesh networkdrawing all possible combination is not necessary. Also draw the location of theinternet gateway site. The main aim of the plot is to get an overall picture of the network. The picture will give informationon the network topology and number of hops between sites and the internet gateway.

Topology:This is the simplest topology to configure in mesh networks. The sites are fairly uniformly distributed and every node can

see every other node. If the area becomes too large, some sites might be too far away from the internet gateway andtherefore needs to hop through many other mesh nodes before reaching the gateway. This will slow down theirconnection. One solution would be to add gateways throughout the mesh (also uniformly distributed across the mesh). Thedisadvantage is the high cost associated with an internet gateway. The preferable solution would therefore be to build aso-called backbone reaching from the gateway throughout the mesh network.If the gateway is in the middle, several backbones might be needed (e.g. star topology) to ensure that everyone gets thesame bandwidth. Figure 1 gives an example of a simple mesh network plot requiring no backbone.

Figure: Basic Wireless Mesh Network

In our system we used both wireless & optical network. For node to node connect Wifi has been used.


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References:

[1] faculty.wiu.edu/Y-Kim2/pd4-1.ppt

[2] netlab.csie.ntut.edu.tw/seminar/year2005/SHC_20060411.ppt

[3] users.crhc.illinois.edu/nhv/09spring.439/slides/ko.lecture.28.ppt

[4] www.cas.mcmaster.ca/~rzheng/course/.../cunqing.ppt

[5]www.ece.gatech.edu/.../CHAPTER12.ppt

[6] www.iaria.org/conferences2009/.../EugenBorcociTutorial.pdf

[7] fif.kr/fiwc2008/docs/3-9.pdf

[8] http://www.cisco.com/web/PT/assets/docs/wireless_mesh.pdf

[9] www.csg.ethz.ch/.../ws06.../WMN-BasicsWS0607-print.pdf

[10] http://www.pcmag.com/encyclopedia/term/54776/wireless-mesh-network


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This portion is directly copied from

Building a Rural Wireless Mesh Network

A do-it-yourself guide to planning and buildinga Freifunk based mesh networkVersion: 0.8David Johnson, Karel Matthee, Dare Sokoya,Lawrence Mboweni, Ajay Makan, and Henk KotzeWireless Africa, Meraka Institute, South Africa30 October 2007


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6. BUILDING THE WIRELESS MESH NETWORK

6.1 Where to Start

Start building the wireless mesh network by configuring all the mesh nodes and wireless

access points in a central location according to the network design document. Mark eachmesh node and wireless access point with the configuration details written on a piece ofpaper and stuck to the device. In this way the later configuration steps will be much easier.It is also good practice to keep a log book with the configuration details and location of eachnode and to record the history of the node. See Appendix G for a form for the planningdetails required for a node, which can also be used as a log sheet for record keeping.

While still at the same central location, test all equipment to ensure that everything isworking correctly. Connect a PC to a mesh node with a LAN cable. Ensure that the PC willrequest an IP address by DHCP. Ping every other mesh node. If the ping is successful,then the mesh node attached to the PC and the other mesh nodes are working. If it is notsuccessful, check the configurations.

Start installing the mesh nodes from the gateway the point where the internet will beconnected to the mesh network. In this way you can confirm that the network is still workingas you install each new mesh node. Connect a PC to the mesh node with a LAN cable.Simply ping the gateway first, and if that is successful, ping any site on the internet toensure that the PC can access the internet.

6.2 Prepare a Wireless Mesh Node

Opening the Linksys package, the contents are as shown in Figure 7 below:

Building a Rural Wireless Mesh Network - A DIY Guide 15

Figure 7: Linksys WRT54GL and package contents

LAN cable

Power supply unit

Linksys

WRT54GL routerLinksys Documentation

(Not needed)


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The following steps are needed to prepare a wireless mesh node:

Upgrading the firmware this will be done for all backbone and normal mesh nodes

Configuration of:

System settings

Wireless settings

LAN settings

OLSR settings

NOTE

1. At anytime during the configuration, you can place the mouse on any text field and a popup window will appear to explain the meaning of the field. For more information you canalso press F1 with the cursor at the text field you want more information about.

2. For each of the four configuration sections (System, Wireless, LAN and OLSR settings)that follow, there is a requirement to restart the Linksys after completing each sectionssettings. You can however choose to complete all four section settings, skipping therestart after each section, before restarting the Linksys. Although skipping the restartafter each section is not advisable, unless you know what you are doing , it saves aconsiderable amount of time as you have to wait a few minutes for the Linksys to restart

each time.


Figure 8: Linksys WRT54GL Wireless Broadband Router

Reset Internet PowerEthernet Ports 1-4


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The first step is to upgrade the Linksys firmware with the Freifunk firmware. That isaccomplished by following the steps outlined below.

UPGRADING THE FIRMWARE - Freifunk

Step 1: Download the Freifunk firmware (see section 4.2)

Step 2: Connect the LAN cable (blue cable found in your Linksys packaging) to yourPC/laptop and to the back of the Linksys on one of the ports labeled 1-4. PleaseDO NOTuse the port labeled Internet.

The LAN cable does not have to be the one that came with the Linksys, anystraight through (not cross-over) LAN cable would do.

Step 3: Ensure that your machine is set to obtain an IP address automatically. (SeeAppendix B Configuration Steps)

Step 4: Connect the Linksys to the power cable (found in the Linksys packaging) andswitch on the power source.

Step 5: Depending on which LAN port of the Linksys you used, the front LEDcorresponding to the port number at the back should be light green. That is, ifyou used port 1 then LED 1 should be on.

If the LED is not on, then please go to Appendix C Troubleshooting FAQ

Step 6: Repair your LAN connection so that you get a 192.168.1.x IP address. (See

Appendix B Configuration Steps)

To check that you have a 192.168.1.xIP address:

In the Network Connections window: right click on Local Area Connection select Status click on the Support tab. You should see an IP address of192.168.1.x, (where 1 x< 255) else go to Appendix C Troubleshooting FAQ

Step 7: Open a web browser and ensure that your browser is NOT set to make webconnections via a proxy. In the address field of the web browser type:192.168.1.1and press [Enter]

This will take you to the setup page of the Linksys router

Note: When requested for a User name andPassword use:

User name: root

Password: admin

Step 8: Click on Administration Firmware Upgrade click on Browse anduse the Choose file window to select the Freifunk firmware (openwrt-g-freifunk-1.4.5-en.bin ) you downloaded click on Upgrade.

During this time the power LED will start blinking and the DMZ LED will be solid

ON or blinking.Note:The message on the screen will say Upgrade is successful. DO NOT



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react to this screen. DO NOT click on Continue. WAIT for 4-6 minutes.Interrupting the upgrading process might cause the Linksys to becomeunuseable!

After about 4-6 minutes the power LED should be permanently ON (NOTblinking) and the DMZ LED should be permanently OFF.

Step 9: Click on Continue

This will/should open the Freifunk.Net Hello! page

Once the Linksys firmware has been upgraded to the Freifunk firmware we can start theconfiguration of the mesh node. As indicated before the following settings need to beconfigured:

System settings

Wireless settings

LAN settings

OLSR settings

Mesh node with wireless IP address 10.1.1.4, as shown in Figure 9 (excerpt from Figure 6)is used as an example.


Figure 9:Configuration of a mesh node


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SYSTEM SETTINGS

Refer to Figure 10 below as an example.

Step 1: Click on the Admin link

Step 2: Click on the System link to configure the system settings

Step 3: Type in your choice of Host Name (Any unique descriptive name to identifythis Linksys with this name the device can be addressed by name)

Step 4: You MUST select a country where you are using the Linksys, so that theacceptable country setting can be determined.

Step 5: Leave all other options untouched. Click on Apply. The following message willappear:

Step 6: Click on the Restart link Click on Restart

The restart process will take a few minutes and automatically refresh when theLinksys is done with the restarting process. This will/should open theFreifunk.Net Hello! page but note that it is now called [Host Name] Hello!page


Figure 10: Freifunk firmware - System settings


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WIRELESS SETTINGS

Refer to Figure 11 below as an example


Step 2: Click on the Wireless link to configure the wireless interface

Step 3: Select Static for the WLAN Protocol

Step 4: Type in your choice of WLAN-IP Address

Step 5: Type in your choice of WLAN Netmask

Step 6: Type in your choice of WLAN Default Route(if any, default is blank)

Step 7: Select Ad Hoc (Peer to Peer)for the WLAN Mode

Step 8: Type in the ESSIDof your choice

Step 9: Type in the BSSIDof you choice.

Note:Always lock the BSSID. You can choose the MAC address of one Linksysand use this for all the other Linksys(es) in the mesh network.

The BSSID is important to specify to allow rejoining mesh networks should themesh ever breaks into at least 2 networks due to a connection going down andlater coming back on.

Step 10: Type in the channel of your choice, usually numbers from 1-13 however,channels available depending on the country selected under the System setting.From the discussion in section 5.3, this can be 1, 6 or 11.

Step 11: Select Auto for both the RX Antenna and TX Antenna, unless you arecertain which antenna you want to use.

Step 12: Leave all other options untouched. Click on Apply. The following message will

appear:


The restart process will take a few minutes and automatically refresh when theLinksys is done with the restarting process.

NOTE The settings in steps 7-10MUSTbe the same for all Linksys(es) on the same

network.



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Figure 11: Freifunk firmware - Wireless settings


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LAN SETTINGS



Step 2: Click on the LAN link to configure the LAN interface

Step 3: Select Static for LAN Protocol

Step 4: Type in your choice of LAN-IP Address

Step 5: Type in your choice of LAN Netmask (use 255.255.255.0unless you havespecial cases for any other netmask)

Step 6: Type in your choice of LAN Default Route (if any)

Step 7: Disable NAT by clicking the check box next to it

Step 8: Disable the Firewall by clicking the check box next to it

Step 9: Click on Apply. The following message will appear:



Step 11: (Skip this step if you skipped step 10)

After the restart the connection is no longer valid. After 10-15 seconds repair theconnection. (See Appendix B Configuration Steps)

Step 12: (Skip this step if you skipped step 10 )

In the address field of the browser, type the in the LAN IP address you specifiedunder LAN IP and press [Enter]



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Figure 12: Freifunk firmware - LAN settings


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OLSR SETTINGS



Step 2: Click on the OLSR link to configure the OLSR settings

Step 3: Under the HNA4text field type in the first three octets of your LAN IP addressfollowed by 0/24. (e.g. If your LAN IP address is 10.2.4.1, then type in10.2.4.0/24

Step 4: If this Linksys is connected to the internet and you want to enable other nodesto access the internet then click on Enable to enable the dynamic gateway -DynGW

Step 5: Leave all other options untouched. Click on Apply. The following message willappear:



NOTE IMPORTANT: Whether you skipped the restart steps during the previoussection settings or not, at this point you MUSTRESTARTthe Linksys.



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6.3 How to configure OLSR to join two distinct mesh networks

In this case we have two disjointed mesh networks, both running OLSR. We use two Linksysboxes to join the two networks. In Figure 14 above (excerpt from Figure 6) we refer to nodes withEthernet addresses 10.3.1.2 and 10.3.1.1.

We assume the following:

The two networks have unique IP addresses; otherwise they can't be joined.

That at MOST one of the networks has an internet gateway (later we will discuss how toensure that a mesh node with internet access advertises it's internet default route to therest of the mesh network).

Software setup

Step 1 Connect the LAN cable (blue cable found in your Linksys packaging) to yourPC/laptop and to the back of the Linksys on one of the ports labeled 1-4. PleaseDO NOTuse the port labeled internet.

Step 2: Log on to the Linksys using ssh or Putty (if using Windows).

Step 3: Edit file /etc/olsrd.conf, Type vi /etc/olsrd.conf

Step 4: Change the interfaces section to the following:

interface eth1 br0

Step 5: Repeat the above steps on the second Linksys


Figure 14:Joining two distinct mesh networks


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Figure 13: Freifunk firmware - OLSR Settings


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Hardware setup

Take a straight (as opposed to crossed) cable, and connect the two Linksyses back-to-back, i.e. connect one end of the cable to one of the 4 network ports labeled 1-4 and the

other end to the corresponding network port 1-4 on the other Linksys. Thus, from ourexample above connect one end of the LAN cable to port 1-4 of node 10.3.1.2 and the otherend to port 1-4 of node 10.3.1.1.

6.4 How to configure a gateway


Figure 15:Configuring a Gateway


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WAN SETTINGS

Refer to Figure 16 below as an example. If your gateway server (10.4.1.2 in theexample above) does not run DHCP then follow steps 1,2,3(a), 4, 5. and 6. Ifyour server does run DHCP then only follow steps 1,2 and 3(b).


Step 2: Click on the WAN link to configure the WAN settings

Step 3: (a) Select Static for WAN Protocol

(b) Select Dynamic for WAN Protocol

Step 4: Under WAN IP, typein an IP address that is within the DHCP IP range of theother Linksys. From the example above, you'd type in 10.4.1.1

Step 5: Under WAN Netmask type in 255.255.255.0

Step 6: Under Default Route, type in the IP address of the firewall. From the exampleabove, you'd type in 10.4.1.2


Figure 16: Freifunk firmware - WAN settings


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6.5 Linking a Mesh Node and an Access Point Back-to-Back

The wireless access point is used to create a hotspot.

The following steps are needed to prepare a wireless access point:

Upgrading the firmware (DD-WRT)

Configuration of:

Setup Basic Setup settings

Wireless - Basic settings

The first step is to upgrade the Linksys firmware to the DD-WRT firmware. That is accomplished byfollowing the steps outlined below.

UPGRADING THE FIRMWARE - DD-WRT

Step 1: Download the DD-WRT firmware (see section 4.2)

Step 2: Connect the LAN cable (blue cable found in your Linksys packaging) to yourPC/laptop and to the back of the Linksys on one of the ports labeled 1-4. PleaseDO NOTuse the port labeled Internet.

The LAN cable does not have to be the one that came with the Linksys, anystraight through (not cross-over) LAN cable would do.

Step 3: Ensure that your machine is set to obtain an IP address automatically. (See

Appendix B Configuration Steps)


Figure 17:Creating a wireless access point


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Step 4: Connect the Linksys to the power cable (found in the Linksys packaging) andswitch on the power source.

Step 5: Depending on which LAN port of the Linksys you used, the front LEDcorresponding to the port number at the back should be light green. That is, ifyou used port 1 then LED 1 should be on.

If the LED is not on, then please go to Appendix C Troubleshooting FAQ

Step 6: Repair your LAN connection so that you get a 192.168.1.x IP address. (SeeAppendix B Configuration Steps)

To check that you have a 192.168.1.xIP address:

In the Network Connections window: right click on Local Area Connection select Status click on the Support tab. You should see an IP address of192.168.1.x, (where 1 x< 255) else go to Appendix C Troubleshooting FAQ

Step 7: Open a web browser and ensure that your browser is NOT set to make webconnections via a proxy. In the address field of the web browser type:192.168.1.1and press [Enter]

This will take you to the setup page of the Linksys router

Note: When requested for a User name andPassword use:

User name: root

Password: admin

Step 8: Click on Administration Firmware Upgrade click on Browse anduse the Choose file window to select the DD-WWRT firmware (dd-wrt.v23_wrt54g.bin) you downloaded click on Upgrade.

During this time the power LED will start blinking.

Note: WAIT for 4-6 minutes. Interrupting the upgrading process mightcause the Linksys to become unuseable!

After about 4-6 minutes the power LED should be permanently ON (NOTblinking) and the DMZ LED should be permanently OFF.

Click on Continue

This will/should open the WRT54GL - Setup page

Once the Linksys firmware has been upgraded to the DD-WRT firmware we can start theconfiguration of the wireless access point. As indicated before the following settings need to beconfigured (in this order):

Wireless - Basic settings

Setup Basic Setup settings



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DD-WRT Wireless Settings


Step 1: Click on Wireless click on Basic Setup

Step 2: Under Basic Settings select AP for Wireless Mode

Step 3: Type in the SSID of the local hotspot under Wireless Network Name (SSID)

Step 4: Under Wireless Channelselect the channel number

Step 5: Leave the rest of the settings as default. Click on Save Settings


Figure 18: Access Point - Wireless setup


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DD-WRT Basic Setup Settings


Step 1: Click on Setup click on Basic Setup

Step 2: Under Internet Connection Type select disabled for Connection Type

Under Network Address Server Settings (DHCP) select DHCP Forwarder forDHCP Type

NOTE: This will automatically reduce the menu options to the ones required frothis configuration.

Step 3: Under Router IP, type in your choice for the LAN IP addressof your accesspoint in the Local IP Addressfield.

Step 4: Type in your choice of Subnet Mask (use 255.255.255.0 unless you havespecial cases for any other netmask)

Step 5: Under Network Address Server Settings (DHCP) and set the DHCP Server tothe LAN IP address of the mesh node

Step 6: Select the appropriate time zone setting under the Time Setting

Step 7: Leave the rest of the settings as default. Click on Save Settings The unit willnow reboot. This will take a few minutes.



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Figure 19: Access Point Basic setup


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APPENDIX A: Acronyms

ATA Analog Telephone Adapter

BSSID Basic Service Set Identifier (this is the MAC address of the wireless interface)

CD Client Device

DHCP Dynamic Host Configuration Protocol

DMZ DeMilitarized Zone

DNS Domain Name System

ESSID Extended Service Set Identifier

GPS Global Positioning System

IP Internet Protocol

LAN Local Area Network

LED Light Emitting Diode

MAC Media Access Control

MN Mesh Node

OLSR Optimized Link State Routing (protocol)

PBX Private Branch eXchange

PC Personal Computer

RFC Request for comment

SSH Secure SHell

SSID Service Set Identifier (Network name - All mesh nodes attempting tocommunicate with each other must share the same SSID)

VSAT Very small aperture terminal

VoIP Voice over internet protocol

WAN Wide Area Network

WAP Wireless Access Point

Wi-Fi IEEE 802.11 wireless standards. Trademark of the Wi-Fi Alliance

WMN Wireless Mesh Network



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APPENDIX B: Configuration Steps

1. Setting up your machine to obtain an IP address automatically

FOR WINDOWS USERS

Click on start

click on Control Panel

click on Network Connections

rightclick on Local Area Connection select Properties select the General tab scroll down the list and select Internet Protocol TCP/IP click on Properties select the General tab select Obtain an IP address automatically click onOK on the Internet Protocol (TCP/IP) Properties window click on OK on the LocalArea Connection Properties window.

2. Repairing your LAN connection

FOR WINDOWS USERS:

Click on start click on Control Panel click on Network Connections rightclick on Local Area Connection select Repair

or for help on repairing a connection:

Click on start click on Help and Support in the search box type Repairing

LAN connection and follow the instructions.

FOR LINUX USERS:

Open a terminal, grant yourself root privileges (e.g. on Ubuntu, type sudo or simply sudo

dhclient eth0 and press [Enter]) and type dhclient eth0, and press [Enter]; eth0is your LAN interface name. You should see an IP address of 192.168.1. x, (where 1 x

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