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4. Wireless Networking Technologies Unlike wired networking that is dominated by a single technology, many wireless networking

technologies have been created, and new variants appear continually.

Wireless technologies can be classified according to network type as follows:

Personal Area Networks (PANs)

Local Area Networks (LANS)

Metropolitan Area Networks (MANs), and

Wide Area Networks (WANs)

Personal Area Networks (PANs)

In addition to the three main network types, wireless networking includes Personal Area Networks.

A PAN technology provides communication over a short distance and

is intended for use with devices that are owned and operated by a single user.

Examples:

Communication between a wireless headset and a cell phone.

Communication between a wireless mouse and a keyboard.

The following three major types of PAN technologies are created:

Type Purpose

Bluetooth Communication over a short distance between a small peripheral device such as a

headset or mouse and a system such as a cell phone or a computer.

Infrared Line-of-sight communication between a small device, often a hand-held controller

and a nearby system such as a computer or an entertainment center.

ZigBee Communication over distances about as large as a residence which allows electrical

appliances to connect to the Smart Grid.

Another type of PAN technology is referred to as Industrial, Scientific, and Medical (ISM) groups.

Governments have reserved three areas of the electromagnetic spectrum for use by these groups as

follows:

26 MHz bandwidth 902 MHz - 928 MHz

83.6 MHz bandwidth 2.4 GHz - 2.484 GHz

125 MHz bandwidth 5.725 GHz - 5.850 GHz

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Characteristics of Bluetooth Technology

Wireless replacement for cables (e.g. headphones or mouse)

Uses 2.4 GHz frequency band

Short distance (up to 5 meters, with variations that extends the range to 10 or 50 meters)

Device is master or slave

Master grants permission to slave

Data rate is up to 721 Kbps

Characteristics of ZigBee Technology

Wireless standard for remote control (low data rate)

Target is industry as well as home automation

Three frequency bands used (869 MHz, 915 MHz, and 2.4 GHz)

Data rate of 20, 40, or 250 Kbps depending on frequency band

Low power consumption

Multiple levels of security being defined

Characteristic of Infrared Technology

Family of standards for various speeds and purposes

Practical systems have range of one to several meters

Directional transmission with a cone covering 30

Data rates between 2.4 Kbps (control) and 16 Mbps (data)

Generally low power consumption with very low power versions

Signal may reflect from surfaces but cannot penetrate solid objects.

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Radio Frequency Identification (RFID)

With the RFID technology, a small tag that contains some identification information that a receiver can

pull (extract) from the tag.

It has the following characteristics:

Over 140 RFID standards exist for a variety of applications

Passive RFIDs draw power from the signal sent by the reader

Active RFIDs contain a battery which may last up to 10 years

Limited distance (active RFIDs extend farther than passive RDFIs)

Can use frequencies from less than 100 MHz to 868-954 MHz

Used for inventory control, sensors, passports, and other applications.

Wireless LAN Technologies and Wi-Fi

IEEE provides most of the standards for wireless LAN technologies which are categorized as IEEE

802.11.

In 1999, a group of vendors who build wireless equipment formed the Wi-Fi Alliance, a non-profit

organization that tests and certifies wireless equipment using the IEEE 802.11 standards.

Today, most consumers associate wireless LANs with the term Wi-Fi because the alliance has received

extensive marketing.

However, a variety of wireless LAN technologies that use various frequencies, modulation techniques

and data rates exits.

In Wi-Fi communications, techniques known as Spread Spectrum techniques are used to do the

following:

Increase overall performance, and

Make transmissions more immune to noise.

With these techniques, the sender of a message uses multiple frequencies to send the different part of a

message (frequency multiplexing).

The major multiplexing techniques used with Wi-Fi are listed as follows:

DSSS (Direct Sequence Spread Spectrum)

FHSS (Frequency Hopping Spread Spectrum), and

OFDM (Orthogonal Frequency Division Multiplexing).

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Wireless LAN Architecture

A wireless LAN consists of three building blocks:

Access points informally called base stations

An interconnection mechanism such as a switch or a router used to connect access points.

A set of wireless hosts also called wireless nodes or wireless stations

There are in principle two types of wireless LANs:

Ad hoc:

Wireless hosts communicate among themselves without a base station

Infrastructure:

a wireless host only communicates with an access point and the access point relays all

packets.

However, in practice, few ad hoc networks exist.

In general, an organization or a service provider deploy a set of access point and each wireless host

communicates through one of the access points

Refer to Figure 16.7 (page 270)

The wired connections that extend to access points usually consist of twisted pair Ethernet.

The set of computers within the range of a given access point is referred to as Basic Service Set (BSS).

Overlap, Association, and 802.11 Frame Format

Issues with a wireless LAN architecture:

1. If a pair of access point are too far apart, a dead zone (a location with no wireless connectivity) will

exist between them.

2. If a pair of access points are too close together, an overlap will exist in which a wireless host can

reach both access points.

3. Most wireless LANs connect to the Internet: an additional wired connection to a router is therefore

needed.

To handle overlaps, IEEE 802.11 networks require a wireless host to associate with a single access point:

a wireless host sends frames to a particular access point,

which then forwards it across the network.

The corresponding frame is provided in Figure 16.9 in page 271.

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Coordination among Access Points

The issue here is about how access points have to behave when a wireless computer moves from the

region of one access point to the region of another.

Two approaches are used:

1. The access points communicate among themselves to ensure a smooth handoff as a wireless

computer moved from the region of one access point to the region of another.

2. Access points operate independently and rely on wireless computers to change their association from

one access point to another.

Wireless WAN Technologies

There are two major categories of Wireless WAN technologies:

Cellular communication systems, and

Satellite communication systems.

Cellular Communication Systems

Cellular communication systems were originally designed to connect the region reached by an access

point (a.k.a. cell) to the public telephone network.

That means to provide voice services to mobile customers.

Today, cellular systems are being used to provide

data services and

internet connectivity.

A cellular architecture is designed as follows:

Each cell contains a tower, and

A group of (usually adjacent) cells is connected to a Mobile Switching Center.

The center tracks a mobile user and manages handoff as the user passes from one cell to another.

When a user moves between two cells that connect to the Mobile Switching Center, the switching center

handles the change, and

When a user passes from one geographic region to another, two Mobile Switching Centers are involved

in the handoff.

Figure 16.14 (page 279) illustrates how cells might be arranged along a highway.

Perfect cellular coverage occurs when each cell forms a hexagon because cells can be arranged in a

honeycomb.

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However, cellular coverage is imperfect:

Most cell towers use omnidirectional antennas that transmit in a circular pattern

Obstructions and electrical interference can attenuate a signal or cause an irregular pattern.

As a result,

o Cells overlap, or

o Gaps exist with no coverage.

Figure 16.15 illustrates ideal and realistic coverage.

Another issue with the uniform honey comb visualization of cells is the fact that a cell size varies

according to the density of cell phones in one area.

For example, in a rural area where the expected density of cell phones is low, a cell size is large

Whereas it is small in an urban setting where many cell phones have to be handled.

Cell Clusters and Frequency Reuse

Cellular communications minimize interference by making sure that pairs of adjacent cells do not

communicate at the same frequency as follows:

Cellular planners employ a cluster approach in which a small pattern of cells is replicated, and

Each cell in a cluster is assigned a unique frequency.

Clusters of size 3, 4, 7, and 12 are commonly used.

Examples of clusters are provided in Figure 16.16 and Figure 16.17shows how a cluster of 7 cells is

replicated.

Generations of Cellular Technologies

The telecommunication industry divides cellular technologies into four generations that are labeled:

1G (1970 – 1980) used analog signal to carry voice.

2G and 2.5G (1990 - ) uses digital signal to carry voice. 2.5G includes some 3G features

3G and 3.5G (2000 - )

focuses on the addition of higher speed data services.

A 3G system offers download rates of 400 Kbps to 2 Mbps and

is intended to support applications such as web browsing and photo sharing

3G allows a phone to roam across North America, Japan, and Europe.

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4G (2008 - )

Focuses on support for real-time multimedia such as television programs or high-speed video

download

4G phones include multiple connection technologies such as Wi-Fi and satellite

communications.

4G systems

o use packet switching, and

o voice transmission is one specific application.

o But in practice, many cellular phone providers still send voice over 3G systems and

o only use 4G protocols for data.

The fact that 4G uses packet switching makes it easy for a cell phone to communicate with an arbitrary

site on the Internet.

VSAT Satellite Technology

A communications satellite is an artificial satellite that relays and amplifies radio telecommunications

signals via a transponder;

A transponder creates a communication channel between a source transmitter and a receiver at different

locations on Earth.

Communications satellites are used for

television,

telephone,

radio,

internet, and

military applications.

There are over 2,000 communications satellites in the Earth’s orbit which are used by both private and

government organizations.

Wireless communication uses electromagnetic waves to carry signals.

These waves require line-of-sight, and are thus obstructed by the curvature of the Earth.

The purpose of communications satellites is to relay the signal around the curve of the Earth allowing

communication between widely separated points.

Communications satellites use a wide range of radio and microwave frequencies.

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To avoid signal interference, international organizations have regulations for which frequency ranges or

"bands" are set for certain organizations to use.

This allocation of bands minimizes the risk of signal interference

A very small aperture terminal (VSAT) is a two-way satellite ground station with a dish antenna that is

smaller than 3.8 meters.

The majority of VSAT antennas range from 75 cm to 1.2 m.

Data rates in most cases, range from 4 kbit/s up to 16 Mbit/s.

VSATs access satellites to relay data from small remote Earth stations (terminals) to other terminals

In a mesh topology, or

master Earth station "hubs" (in star topology).

Some of the uses of VSAT technology follows:

point-of-sale transactions using credit cards,

Internet access

polling of RFID data,

VoIP or video

Many businesses also use VSAT technology to link all their stores.

For example, CVS, Walgreens, Pizza Hut, Taco Bell, and Walmart.

Network Address Translation (NAT)

Page 406 – 408

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Exercises:

1. What are the four categories wireless technologies in use today?

o Personal Area Networks (PANs)

o Local Area Networks (LANS)

o Metropolitan Area Networks (MANs), and

o Wide Area Networks (WANs)

2. Name the three major types of wireless PAN technologies and give a brief description of each.

Type Purpose

Bluetooth Communication over a short distance between a small peripheral device such

as a headset or mouse and a system such as a cell phone or a computer.

Infrared Line-of-sight communication between a small device, often a hand-held

controller and a nearby system such as a computer or an entertainment center.

ZigBee Communication over distances about as large as a residence which allows

electrical appliances to connect to the Smart Grid.

3. What are the characteristics of the Bluetooth technology?

Wireless replacement for cables (e.g. headphones or mouse)

Uses 2.4 GHz frequency band

Short distance (up to 5 meters, with variations that extends the range to 10 or 50 meters)

Device is master or slave

Master grants permission to slave

Data rate is up to 721 Kbps

4. what is ZigBee, and where is it used?

ZigBee is a personal Area Network (PAN) technology . It is used for communication over distances about

as large as a residence which allows electrical appliances to connect to the Smart Grid.

5. what is RFID and where is it used?

Radio Frequency Identification (RFID) technology consists of a small tag that contains some identification

information that a receiver can pull (extract) from the tag.

Passive RFIDs draw power from the signal sent by the reader, and

Active RFIDs contain a battery which may last up to 10 years

Limited distance (active RFIDs extend farther than passive RDFIs)

Can use frequencies from less than 100 MHz to 868-954 MHz

It is used for inventory control, sensors, passports, and other applications.

6. Describe the spread spectrum technique used in Wi-Fi communications.

With spread spectrum technique, the sender of a message uses multiple frequencies to send the different

part of a message (frequency multiplexing).

The major multiplexing techniques used with Wi-Fi are:

DSSS (Direct Sequence Spread Spectrum)

FHSS (Frequency Hopping Spread Spectrum), and

OFDM (Orthogonal Frequency Division Multiplexing).

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7. What are the three building blocks of a wireless LAN?

The building blocks of a wireless LAN are:

o Access points informally called base stations

o An interconnection mechanism such as a switch or a router used to connect access points.

o A set of wireless hosts also called wireless nodes or wireless stations

8. What are the two types of wireless LANs?

The two types of wireless LAN are: Ad hoc and infrastructure.

9. Give a description of each of the types of wireless LANs.

o Ad hoc: Wireless hosts communicate among themselves without a base station, and

o Infrastructure: a wireless host only communicates with an access point and the access point relays all

packets.

10. What are the two major issues with a wireless LAN architecture?

The two major issues with a wireless LAN architecture are signals overlaps and dead zones.

11. How did the IEEE 802.11 recommend handling overlaps?

IEEE 802.11 networks require a wireless host to associate with a single access point in order to handle

overlaps,: a wireless host sends frames to a particular access point, which then forwards it across the

network.

12. What are the two approaches used for coordinating among access points?

The two approaches used for coordinating among access points are:

o The access points communicate among themselves to ensure a smooth handoff as a wireless computer

moved from the region of one access point to the region of another.

o Access points operate independently and rely on wireless computers to change their association from

one access point to another.

13. An 802.11 header contains two destination addresses. Explain the purpose of each.

One destination address is the access point’s MAC address and the other is the router’s MAC address.

14. What are the two major categories of wireless WAN?

The two major categories of Wireless WAN technologies are cellular communication systems, and satellite

communication systems.

15. What are the primary usages of cellular systems today?

The primary usages of cellular systems today are to provide voice services, data services, and internet

connectivity to mobile customers.

16. Give a brief description of a cellular architecture.

A cellular architecture is designed as follows:

Each cell contains a tower, and

A group of (usually adjacent) cells is connected to a Mobile Switching Center.

The center tracks a mobile user and manages handoff as the user passes from one cell to another.

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17. In a cellular system, what happens when a user moves between two cells?

When a user moves between two cells that connect to the Mobile Switching Center, the switching center

handles the change and when he passes from one geographic region to another, two Mobile Switching

Centers are involved in the handoff.

18. When do you have a perfect cellular coverage in a cellular system?

Perfect cellular coverage occurs when each cell forms a hexagon because cell can be arranged in a

honeycomb.

19. Why are cellular coverages not perfect?

Cellular coverages are imperfect because most cell towers use omnidirectional antennas that transmit in a

circular pattern and obstructions and electrical interference can attenuate a signal or cause an irregular

pattern. As a result, cells overlap or gaps exist with no coverage.

20. How do cellular communications minimize interference?

Cellular communications minimize interference by making sure that pairs of adjacent cells do not

communicate at the same frequency.

21. What is a cell cluster, and how does a designer use clusters?

A cell cluster is a group of 3, 4, 7, or 12 adjacent cells in which each cell is assigned a unique

frequency.

A cellular designer replicates cell clusters over a geographic region.

22. Give a brief description of each of the four generations of cellular technologies.

1G (1970 – 1980) used analog signal to carry voice.

2G and 2.5G (1990 - ) uses digital signal to carry voice. 2.5G includes some 3G features

3G and 3.5G (2000 - )

focuses on the addition of higher speed data services.

A 3G system offers download rates of 400 Kbps to 2 Mbps and

is intended to support applications such as web browsing and photo sharing

3G allows a phone to roam across North America, Japan, and Europe.

4G (2008 - )

Focuses on support for real-time multimedia such as television programs or high-speed video

download

4G phones include multiple connection technologies such as Wi-Fi and satellite communications.

4G systems use packet switching, and voice transmission is one specific application. But in practice,

many cellular phone providers still send voice over 3G systems and only use 4G protocols for data.

23. What is a communication satellite?

A communications satellite is an artificial satellite that relays and amplifies radio telecommunications

signals via a transponder

24. What is a transponder?

A transponder is a device that creates a communication channel between a source transmitter and a

receiver at different locations on Earth.

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25. What are the different usages of communications satellites?

Communications satellites are used for television, telephone, radio, internet, and military applications.

26. What types of signals are used in a communication satellite?

Communication satellite uses electromagnetic waves to carry signals.

27. What is the purpose of communications satellites?

The purpose of communications satellites is to relay the signal around the curve of the Earth allowing

communication between widely separated points.

28. How are the signal interferences avoided in communications satellites?

To avoid signal interference, international organizations have regulations for which frequency ranges or

"bands" are set for certain organizations to use.

29. What is a VSAT?

A very small aperture terminal (VSAT) is a two-way satellite ground station with a dish antenna that is

smaller than 3.8 meters.

30. What is the purpose of a VSAT?

The purpose of VSATs is to access satellites to relay data from small remote Earth stations (terminals) to

other terminals in mesh topology, or master Earth station "hubs" (in star topology).

31. What are the different uses of VSAT technology?

Some of the uses of VSAT technology follows:

point-of-sale transactions using credit cards,

Internet access

polling or RFID data,

VoIP or video

Many businesses also use VSAT technology to link all their stores.

32. How many satellite are used in GPS and how accurate is a GPS system?

24 satellites are used, and the accuracy is between 20 and 2 meters.

33. Give a brief description of NAT.