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Ad hoc- chapter 1

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Khoula Al Sadi

on 30 October 2013

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Transcript of Ad hoc- chapter 1

Heinrich Hertz (1857 to 1894) built on the discoveries of Maxwell by proving that electromagnetic waves travel at the speed of light and that electricity can be carried on these waves.
How Bandwidth Is Achieved from RF Signals
Ad Hoc Mobile Wireless Networks
Chapter I

Is a global professional society with over 350,000 members. The IEEE’s mission is to “promote the engineering process of creating, developing, integrating, sharing, and applying knowledge about electro and information technologies and sciences for the benefit of humanity and the profession.”

To networking professionals, that means creating the standards that we use tocommunicate.

The IEEE is probably best known for its LAN standards, the IEEE 802 project.

Is a global, nonprofit industry trade association with over 200 member companies.

The Wi-Fi Alliance is devoted to promoting the growth of wireless LANs (WLANs).

One of the Wi-Fi Alliance’s primary tasks is
to ensure the interoperability of WLAN products by providing certification testing

During the early days of the 802.11 standard, the Wi-Fi Alliance further defined it and provided a set of guidelines to assure compatibility between different vendors.

Products that pass the Wi-Fi certification process receive a Wi-Fi Certified certificate
Commonly known as the ISO
is a global, nongovernmental organization that identifies business, government, and society needs and develops standards in partnership with the sectors that will put them to use.

The ISO is responsible for the creation of the Open Systems Interconnection (OSI) model,which has been a standard reference for data communications between computers since the late 1970s.

The OSI model is the cornerstone of data communications, and learning to understand it is one
of the most important and fundamental tasks a person in the networking industry can undertake. ?????

(( Wireless Standards and Regulatory Committees ))
Differentiate wireless and wired networks.

Explain the advantages and disadvantages of wireless technology.

Identify and understand the different Wireless Standards and Certifications.
Wireless Standards and Committees.

Wireless Local-Area Networks

How Bandwidth Is Achieved from RF Signals

Modulation Techniques and How They Work

General Wireless Technologies

Original 802.11 Topologies

Federal Communications Commission (FCC)

Most Computer-related Hardware and technologies are based on some standards, an wireless LAN are no exception.

IEEE 802.11, also referred to as
Wireless Fidelity (Wi-Fi)
, is the standard for providing local area network (LAN) communications using radio frequencies (RF).

IEEE 802.11 is actually a group of standards that work together to provide wireless networking.

There are organizations that define and support the standards that allow hardware from different manufactures to function seamlessly

Is independent United states government agency, directly responsible to Congress.

It was established by the communication Actof 1934 and is charged with regulating interstate and international communications by radio, television, wire, satellite, and cable.

Most Countries have govering bodies that function similary to the FCC
The FCC and the respective controlling agencies in the other countries typically regulate two categories of wireless communications:
licensed and unlicensed

Unlicensed users do not have to go through the license application procedures before they can install a wireless system.

ISM and UNII Bands
The FCC makes establishes rules limiting which frequencies Wireless LANs can use and the output power on each of those frequency bands.

The FCC has specified that wireless LAN can use the Industrial, Scientific, and Medical (ISM) bands, which are License free.

ISM bands are located starting at 902MHz, and 5.8 GHz and vary in width from about 26 MHz to 150 MHz
Both licensed and unlicensed communications are
typically regulated in the following five areas:


Maximum power of the intentional radiator

Maximum equivalent isotropically radiated power (EIRP)

Use (indoor and/or outdoor)
International Telecommunication Union
Radiocommunication Sector (ITU-R)
A global hierarchy exists for management of the RF spectrum worldwide.

The ITU-R maintains a database of worldwide frequency assignments and coordinates spectrum management through five administrative regions.
The ITU-R maintains a database of worldwide frequency
assignments and coordinates spectrum management through five administrative regions.

Region A: North and South America
Inter-American Telecommunication Commission (CITEL)

Region B: Western Europe
European Conference of Postal and Telecommunications Administrations (CEPT)
Region C: Eastern Europe and Northern Asia
Regional Commonwealth in the field of Communications (RCC)
Region D: Africa
African Telecommunications Union (ATU)
Region E: Asia and Australasia
Asia-Pacific Telecommunity (APT)
Region B: Western Europe
European Conference of Postal and Telecommunications
Administrations (CEPT)
Region C: Eastern Europe and Northern Asia
Regional Commonwealth in the field of
Communications (RCC)
Region D: Africa
African Telecommunications Union (ATU)
Region E: Asia and Australasia
Asia-Pacific Telecommunity (APT)
Within each region, local government RF regulatory bodies such as the following manage the RF spectrum for their respective countries:

Australia, Australian Communications Authority (ACA)

Japan, Association of Radio Industries and Businesses (ARIB)

New Zealand, Ministry of Economic Development

United States, Federal Communications Commission (FCC)
Institute of Electrical and Electronics Engineers (IEEE)
Wi-Fi Alliance
The Wi-Fi Alliance has certified over 1,500 Wi-Fi products for interoperability since testing began in April 2000.

Certification includes three categories:
Wi-Fi products based on IEEE radio standards

Wi-Fi wireless network security

Support for multimedia content over Wi-Fi networks

Wi-Fi products based on IEEE radio standards
, 802.11
, 802.11
in single-mode,
dual-mode (802.11b and 802.11g), and multiband (2.4 GHz and 5 GHz) products
Wi-Fi wireless network security
Wi-Fi Protected Access (WPA), Personal and Enterprise;
Wi-Fi Protected Access 2 (WPA2), Personal and Enterprise
Support for multimedia content over Wi-Fi networks
Wi-Fi Multimedia (WMM)
Wi-Fi Alliance’s WPA2 security standard mirrors the IEEE’s
security standard.

The Wi-Fi Alliance’s WMM standard mirrors theIEEE’s

Quality of Service (QoS) standard.
International Organization for Standardization
Wireless Local-Area Networks
How Bandwidth Is Achieved from RF Signals
Lesson two
WLAN is a LAN that does not need cables to transfer data between devices.

This is accomplished by way of Radio Frequencies (RF).

With RF, the goal is to send as much data as far as possible and as fast as possible.
To achieve bandwidth from RF signals, you need to send data as electrical signals using some type of
emission method.
One such emission method is known as
Spread Spectrum.

To place data on the RF signals, you use a
modulation technique
. Modulation is the addition of data to a carrier signal.
To send music, news, or speech over the airwaves, you use frequency modulation (FM) or amplitude modulation (AM). The last time you were sitting in traffic listening to the radio, you were using this technology.

Is Communication technique characterized by wide bandwidth and low peak power.

Spread spectrum technology allows us to take the same amount of information that we previously would have sent using a narrow band carrier signal and spread it out over a much larger frequency range

For example, we may use 1 MHz at 10 Watts with narrow band, but 20 MHz at 100mW with spread spectrum.

By using a wider frequency spectrum, we reduse the prbability that the data will be corrupted or jammed.
Unlicensed Frequency Bands Used in WLANs
In wireless networking, when you refer to bandwidth it refer to the
width of an RF channel.
not to data rate.

When referring to bandwidth in a wireless network, the standard unit of measure is the
Hertz (Hz). A Hertz measures the number of cycles per second. One Hertz is one cycle
per second
Extremely Low Frequency
Extremely High Frequency
In fact, the data you send using WLANs is either in the 900-MHz, 2.4-GHz, or 5-GHz frequency ranges.
This places you in ........???.............
and ............???.................

Band starts at 902 MHz and goes to 928 MHz

It is the most widely used frequency range in WLANs.
It is used by the 802.11, 802.11b, 802.11g, and 802.11n IEEE standards. The 2.4-GHz frequency range that can be used by WLANs is subdivided into channels that range from 2.4000 to 2.4835 GHz.
Examples: cordless phone.
Some channels overlap with others and cause
With 802.11b and 802.11g, the energy is spread out over a wide area of the band.
With 802.11b or 802.11g products, the channels have a bandwidth of 22 MHz.
This allows three nonoverlapping, non interfering channels to be used in the same area.

The 2.4-GHz range uses direct sequence spread spectrum (
) modulation.
Data rates of 1Mbps, 2Mbps, 5.5Mbps,
and 11Mbps are defined for this range.
900 MHz
The 5-GHz range is used by the 802.11a standard and the new 802.11n draft standard.

In the 802.11a standard, data rates can range from 6 Mbps to 54 Mbps. 802.11a devices were not seen in the market until 2001, so they do not have quite the market penetration as 2.4-GHz range 802.11 b devices.

The 5-GHz range is also subdivided into channels, each being20-MHz wide. A total of 23 nonoverlapping channels exist in the 5-GHz range.
The 5-GHz ranges use Orthogonal Frequency Division Multiplexing (OFDM)
Modulation Techniques and How They Work
What is Modulation?

Modulation is the process of adding data to carrier by altering the amplitude, frequency, or phase of the carrier in a controlled manner
Is the physical Layer Function
Is the process which the radio tranceiver prepare the digital signal within the NIC for transmission over the airwave.
The volume of the signal

The timing of the signal between peaks

The pitch of the signal
Wireless networks use a few different modulation techniques, including these:
Multiple-Input Multiple-Output (MIMO)
Direct Sequence Spread Spectrum

IS very widely known and the most used of the Spread spectrum types, owing most of its popularity to its ease of implementation and high data rates.

The majority of wireless LAN equipment on the market now a days use DSSS technology.

DSSS is the method of sending data in which the transmitting and receiving system are both on 22 MHz-wide set of frequencies.

The wider channel enable device to transmit more information at higher data rate compare with FHSSS.
Multiple In, Multiple Out.

MIMO is a technology that is used in the new 802.11n specification.

A device that uses MIMO technology uses multiple antennas for receiving signals (usually two or three) in addition to multiple antennas for sending signals.

With the use of MIMO technology, an access point (AP) can talk to non-MIMO-capable devices and still offer about a 30 percent increase in performance of standard 802.11a/b/g networks.

How DSSS works
DSSS combines a data signal at the sending station with the higher data rate bit sequence, which refer as
Chiping code
or processing gain
A high processing gain increase the signal resistance to interference

OFDM is not considered a spread spectrum technology Using OFDM

OFDM is not used in 802.11b because 802.11b devices use DSSS.

802.11g and 802.11a both used OFDM.

The way they are implemented is a little different because 802.11g is designed to operate in the 2.4-MHz range along with 802.11b devices.
How OFDM works
You can achieve the highest data rates with the maximum resistance to corruption of the data caused by interference.

OFDM defines a number of channels in a frequency range. These channels are further divided into a larger number of small-bandwidth subcarriers. The channels are 20 MHz, and the subcarriers are 300 kHz wide. You end up with 52 subcarriers per channel. Each of the subcarriers has alow data rate, but the data is sent simultaneously over the subcarriers in parallel.
How MIMO works
MIMO technology can offer data rates higher than 100 Mbps by multiplexing data streams simultaneously in one channel. In other words, if you want data rates higher than 100-Mbps, then multiple streams are sent over a bonded channel, not just one.

Using advanced signal processing, the data can be recovered after being sent on two or more
spatial streams.
Wireless Personal Area Network
A WPAN is a network that is designed to operate within a 20-foot range.

The most common WPAN is Bluetooth where communication occur on the 2.4-GHz spectrum
■ The range is short—about 20 feet.
■ Eight active devices
■ Unlicensed 2.4-GHz spectrum
■ Called a piconet
A WPAN has the following characteristics:
Bluetooth uses Frequency Hopping Spread Spectrum (FHSS).
It operates on the same frequency as 802.11b and 802.11g.
Bluetooth piconets
consist of up to eight active devices but can have many inactive devices.

WPANs usually fall into the unlicensed 2.4-GHz spectrum and are standardized by the 802.15 IEEE workgroup.
WLANs have the following characteristics:
■ 2.4-GHz or 5-GHz spectrum.
■ A larger range than a WPAN—close to 100 meters from AP to client.
■ To achieve further distance, more power output is required.
■ It’s not personal; rather, more clients are expected.
■ WLANs are very flexible, so more than eight active devices/clients are expected, unlike
It can scale from very small home offices to large enterprise network
Normally you find a mix of dual-band wireless access points, laptops, and desktops in a WLAN.

A WLAN operates in either the 2.4-GHz spectrum for 802.11b/g or the 5-GHz
spectrum for 802.11a.

The frequency spectrums used by 802.11a/b, g, and n are all unlicensed.

What makes WLANs flexible is the fact that the APs and clients are dual-band.

This makes it easy to deploy different transmission methods in different areas, and most clients can still operate.
A wireless metropolitan-area network (WMAN)

covers a large geographic area and has the following characteristics:

■ Speeds decrease as the distance increases.

■ Close to broadband speeds versus Ethernet speeds.

■ Used as a backbone, point-to-point, or point-to-multipoint.

■ Most well-known is WiMax
WMANs are used as
backbone services, point-to-point, or even point-to-multipoint links
Sometimes, a WMAN can use unlicensed frequencies.
It’s normal for the speeds in a WMAN to decrease with distance.
The most widely known WMAN is WiMax (802.16b).
WiMax can be used to offer last-mile access as an alternative to broadband services such as DSL or cable connections.

WiMax is an excellent solution where facilities or distance are a limitation. With WiMax, you pay a service provider for access, because the cost of deployment is normally very high.
A wireless wide-area network (WWAN) covers a large geographic area.

WWANs have the following characteristics:
■ Low data rates
■ Pay-for-use
■ High cost of deployment
WWANs usually are very expensive to deploy.

To better understand what a WWAN is, consider your cellular service. Your cell service is a WWAN and probably offers data access as well as voice access.

The data rates are probably around 115 kbps, although some providers offer higher data rates. The most widely deployed WWAN technologies are Global System for Mobile Communication (GSM) and Code Division Multiple Access (CDMA).

Payment for data access or even voice access is typically based on usage.

The original topologies, defined by the 802.11 committees, including the following:
■ Ad hoc mode
■ Infrastructure mode

Original 802.11 Topologies
Ad Hoc Networks

Ad hoc networks don’t require a central device to allow them to communicate. Rather, one device sets a group name and radio parameters, and the otheruses it to connect.
This is called a Basic Service Set (BSS)
, which defines the area in which a device is reachable.

Because the two machines don’t need a central device to speak to each other, it is called an
Independent Basic Service Set (IBSS)
. This type of ad hoc network exists as soon as two devices see each other.
Infrastructure Mode
In ad hoc network:
Each computer has only one radio.

Because there is only one radio, the throughput is lower and acts as a half-duplex device, because you can’t send and receive at the same time.

issue refering the less control .
Infrastructure mode wireless networking bridges (joins) a wireless network to a wired Ethernet network.

Infrastructure mode wireless also supports central connection points for WLAN clients.
A client is called a station (STA), and an AP is called an infrastructure device.

An AP is actually a cross between
a hub and a bridge:

There is one radio, which cannot send and receive at the same time. This is where the AP is likened to a hub. It’s a half-duplex operation.

APs have some intelligence that is similar to that of a bridge. That is how an AP cansee a frame and decide to forward it based on MAC addresses.

To join the WLAN, the AP and all wireless clients must be configured to use the same SSID.

Wireless frames are more complex:
Wireless frames can have three or 4 MAC addresses. 2 of them are the source and destination MAC addresses, and 1 is the AP’s MAC address that is tied to a workgroup

Wireless Cell

The client traffic is passed through the controller and then is forwarded to the wired network, called the
distribution system.
Is how a client accesses the Internet, file servers, printers, and anything else available
on the wired network.
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