Guide to

Wireless Communications

2

Objectives

Explain how the major wireless technologies are used today - WiFi

Describe the applications used in wireless technology

List and explain the advantages of wireless technology

List and explain the disadvantages of wireless technology

3

Wireless – the hype?

Wireless communications is the next major event in the history of technology

Wireless communications will revolutionize how we live

Users will be able to access digital resources no matter where they find themselves

4

How Wireless Technology Is Used

Wireless refers to any device that does not use wires

Wireless communications refers to the transmission of user data without wires

5

Wireless Applications

Wireless applications are found anywhere employees need mobility, including in the following industries:EducationMilitaryBusiness EntertainmentTravelConstructionWarehouse managementHealth care

6

Wireless Communications in Industries

Education—classrooms, presentations, libraries, access anywhere on campus

Military—Universal Handset, a 1.5 lb. device allows full motion video, cellular and satellite communications, and Internet access

Business—office space where traditional infrastructure does not exist, such as conference room or hotel room

7

Wireless Communications in Industries

Entertainment—barcodes on tickets validated by handheld readers; fans accessing game statistics, watching replays, ordering concessions through notebook computers or PDAs

Travel—global positioning systems (GPS) providing emergency roadside assistance; airline passengers using wireless notebooks or PDAs

8

Wireless Communications in Industries

Construction—scheduling construction phases and employee travel, completing payroll, diagnosing equipment

Warehouse Management—inventory, shipping, reading bar-coded pallet labels

Health Care—tracking dispensed medicine, verifying patients’ bar-coded armbands, accessing patient records

9

Current Wireless Systems

Fixed Wireless Access (last mile)

Wide Area Wireless Data Services (WWANs)Cellular Systems

Satellite Systems & Paging Systems

HomeRF (SWAP) (now dead?)

Bluetooth

Wireless LANs (WiFi)

WiFi5

10

SWAP

Shared Wireless Access Protocol (SWAP) defines wireless computer networks Allows wireless data and voice communication

from distances up to 150 feet at speeds up to 10 million bits per second (megabits or Mbps)

Established by HomeRF Working Group, comprised of over 50 different companies

Uses wireless home networking adapter that sends data over radio waves throughout the home, as seen in Figure 1-1

11

Home Wireless Network

12

HomeRF

Shared Wireless Access Protocol (SWAP), Home RF is an open industry specification that allows wireless devices to share information around homeOperates in license-free 2.4 GHz frequency and

uses frequency-hopping spread spectrum (FHSS)Provides quality-of-service (QoS) that prioritizes

time-sensitive transmissionsVersion 1.0, introduced in 2000, transmits at

1.6 Mbps, but version 2.0, released in 2001, transmits at 10 Mbps

13

14

Bluetooth

Uses devices with small radio transceivers, called radio modules, built onto microprocessor chips

Special software, called a link manager, identifies other Bluetooth devices, creates links with them, and sends and receives data

Transmits at up to 1 Mbps over a distance of 33 feet and is not impeded by physical barriers

Bluetooth products created by over 1500 computer, telephone, and peripheral vendors

15

Bluetooth Headset

The Bluetooth headset automatically establishes a connection with the telephone

16

Piconet

Two or more Bluetooth devices that send and receive data make up a personal area network (PAN), also called a piconet

Figure 1-3 shows a Bluetooth network

Bluetooth was named after the 10th century Danish King Harold Bluetooth, who was responsible for unifying Scandinavia

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Bluetooth Network

18

Network Topology

Two types of Bluetooth network topologies PiconetScatternet (collection of piconets)

Two Bluetooth devices within range automatically connectOne device is the master, controlling all wireless

trafficThe other is the slave, taking commands from

the master.

19

Piconets

A piconet is one master and at least one slave using the same channel

An active slave is sending transmissions

A passive slave is not actually participating

20

Bluetooth Issues

Many challenges face BluetoothCostLimited supportShortcomings in protocol itselfPositioning in marketplaceConflicts with other devices in radio spectrum

21

Cost

Chips have decreased in price to about $15 from a high of over $75Not advantageous to replace a $7 cable with a

$15 chip Many think cost must come down to about

$5 before Bluetooth reaches competitive advantage

22

Limited Support

Bluetooth is caught in “chicken or egg” scenarioBecause of low market penetration, Bluetooth

is not fully supported by hardware and software vendors

Users reluctant to purchase technology that is not fully supported

Microsoft is “straddling the fence”Provides Bluetooth support for Pocket PC 2002 Does not support Bluetooth in Windows XP

23

Protocol Limitations

Major limitation is no hand-off between piconetsUnlike cell phone switching, Bluetooth

connection is broken and must be restored with new master when device moves from one piconet area to another

Bluetooth provides less than optimal security by authenticating devices instead of users

Devices cannot determine how function of other devices can be used in cooperating setting

24

Market Position

Current position is between IEEE 802.11x WLANs and cell phonesWLAN is preferred technology for connecting

wireless devices to form networkWLAN is mature, robust, flexible, popular

technologyTrend today is fewer devices instead of more,

and cell phones have integrated capabilities that Bluetooth lacks

25

Spectrum Conflict

The 2.4 GHz band that Bluetooth uses conflicts with IEEE 802.11b WLANsWLAN may drop connection when detects

another device sharing its frequencyMost obvious fix is moving Bluetooth device

away from WLANMany vendors offer products that let Bluetooth

and 802.11b WLANs share spectrumNew 802.11a WLAN standard uses a different

frequency, eliminating the conflict

26

Wireless Local Area Network (WLAN)

Based on the Institute of Electrical and Electronic Engineers (IEEE) 802.11b networking standard

WLAN computers transmit up to 11 Mbps at distances of 375 feet

IEEE 802.11a standard increases bandwidth to 54 Mbps

Figure 1-8 shows a WLAN warehouse network

802.11 often called wireless ethernet

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WLAN Warehouse Network

28

WLAN Applications

Almost nonexistent until 2000, WLANs have experienced astonishing growth, with sales expected to top $34 billion by 2004

WLANs have broad range of uses including colleges and schools, businesses, airports, warehouses, shopping malls, and stadiums

WLANs have taken the world by storm and the list of users grows daily

29

How WLANs Operate

Although a variety of radio frequency WLANs exist, different products share similarities and operate similarly

Only two components are required for a wireless networkWireless network interface (NIC) cardsAccess points (AP)

30

Wireless NIC and Access Point (AP)

Each computer on WLAN uses wireless network interface card (NIC) with built-in antenna

Wireless NIC sends signals through radio waves to a fixed access point (AP)AP point may be attached to a wired LANFigure 1-9 shows an AP and wireless NIC

WLANs also used in office environments, as shown in Figure 1-10

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Access Point and Wireless NIC

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Office WLAN

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Wireless Network Interface Card

NIC connects computer to network so it can send and receive data

On wired network, NIC has a port for a cable connector, as seen in Figure 6-1

On wireless network, the NIC has an antenna to send and receive RF signalsNIC changes internal data from parallel to

serial, divides data into packets with sending and receiving addresses, determines when to send packet, and transmits packet

34

Integrated Wireless NICs

Some vendors plan integrating components of wireless NIC onto single chip on motherboard

Some notebook manufacturers will integrate wireless NIC into top of notebook behind LCD displayThis will keep RF waves away from

motherboard

35

Software for Wireless NICs

Software may be part of operating system itselfWindows XP has software integrated while

previous versions of Windows do notSoftware may be separate program loaded

into the computerAll operating systems before Windows XP,

including Linux, require loading softwareOperating systems for PDAs may soon

integrate software to recognize a wireless NIC

36

Access Point

An access point (AP) has three main parts An antenna and a radio

transmitter/receiver An RJ-45 wired

network interface to connect to a wired network

Special bridging software

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Access Point

38

Functions of an Access Point

Access point has two basic functionsActs as base station for wireless networkActs as bridge between wireless and wired

networkBridges are LAN connectors at MAC level

See Figure 6-7

39

Access Point as a Bridge

40

Characteristics of an Access Point

Range approximately 375 feet (115 meters)Generally supports over 100 users

One access point for each 50 users with light email and basic Internet access

One access point per 20 users for heavy network access and large file transfer

APs typically mounted on ceiling, but AC power may be a problemPower over Ethernet feature delivers DC power

through standard unshielded twisted pair (UTP) Ethernet cable

41

Ad Hoc Mode

Ad Hoc Mode or peer-to-peer mode lets wireless clients communicate among themselves without an access pointOfficially called Independent Basic Services

Set (IBSS), this mode is easy to set up, but it does not have access to a wired network

See Figure 6-8

42

Ad Hoc Mode

43

Infrastructure Mode

Infrastructure Mode, also called Basic Service Set (BSS), has wireless clients and an access point

More access points can be added to create an Extended Service Set (ESS)See Figure 6-9

44

Extended Service Set (ESS)

45

Features of Access Points

Coverage area should overlap when using multiple access pointsWireless clients survey radio frequencies to

find an AP that provides better serviceA seamless handoff occurs when client

associates with new AP

46

ESS and Subdivided Networks

Drawback of ESS WLANs is that all wireless clients and APs must be part of same network to allow roaming

Network managers like to subdivide networks into subnets, but this prevents clients from roaming freelyAlternative may be software that tricks network

into seeing subnets as one network

47

Wireless Gateway

Devices that follow 802.11 standard are becoming less expensive and more popular

Wireless Gateway has made future of HomeRF very shaky

Wireless gateway has wireless access point, Network Address Translator (NAT) router, firewall, connections for DSL and cable modems, and other features

48

IEEE 802.11

Introduced in 1990Defines cable-free local area network with

either fixed or mobile locations that transmit at either 1 or 2 Mbps

Uses OSI model with functions of PHY and MAC layer performing WLAN featuresSee Figure 6-10

Slow bandwidth insufficient for most network applications

49

WLAN features in PHY and MAC layers

50

IEEE 802.11b

1999 amendment to 802.11 standardAdded two higher speeds: 5.5 and 11 MbpsCalled Wi-FiQuickly became standard for WLANs

51

Wireless changes to layers

PhysicalData Link

52

Physical Layer

Physical layer that sends and receives signals from network is divided into two partsSee Figure 6-11

Physical Medium Dependent (PMD) sublayer defines how data is transmitted and received through the medium

Physical Layer Convergence Procedure (PLCP) performs two basic functions, as seen in Figure 6-12 Reformats data into frame PMD sublayer can

transmitListens to determine when data can be sent

53

PHY Sublayers

54

PLCP Sublayer

55

Physical Layer Convergence Procedure Standards

Based on direct sequence spread spectrum (DSSS)

Reformats data from MAC layer into frame that PMD sublayer can transmitSee Figure 6-13

Frame has three parts Preamble and Header transmit at 1 MbpsData portion, containing from 1 to 16,384 bits,

may be sent at faster rate

56

PLCP Frame

57

Physical Medium Dependent Standards

Frame created by PLCP passes to PMD sublayer where binary 1’s and 0’s are translated into radio signals for transmission

802.11b standard uses Industrial, Scientific, and Medical (ISM) band for transmissionsMay use 14 frequencies, beginning at 2.412

GHz and incrementing in .005 GHz stepsSee Table 6-1

58

802.11b ISM Channels

59

Medium Access Control Layer Changes

802.11 Data Link layer has two sublayersLogical Link Control (LLC), used in 802.11b

wireless networks with no change from wired network functions

Media Access control (MAC) contains all changes necessary for 802.11b WLANs

60

Two Kinds of Coordination

Coordination necessary among devices sharing same RF spectrum

Two kinds of coordinationDistributed coordination function is 802.11b

standardPoint coordination function is optional

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Distributed Coordination Function

Channel access methods refer to different ways of sharing

ContentionComputers compete for use of networkMay cause collisions that result in scrambled

messages, as seen in Figure 6-14Must first listen to be sure no other device is

transmitting

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Collision

63

CSMA/CD

802.3 Ethernet standard uses contention with “listening” as channel access methodCarrier Sense Multiple Access with Collision

Detection (CSMA/CD) After a collision, each computer waits a random

amount of time, called backoff interval, before attempting to resend

See Figure 6-15

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CSMA/CD

65

Distributed Coordination Function (DCF)

802.11b wireless networks cannot use CSMA/CD because radio signals drown out ability to detect collisions

802.11b uses Distributed Coordination Function (DCF) with modified procedure known as Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA)Following collision, clients wait random

amount of slot time after medium is clearThis technique helps reduce collisions

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Packet Acknowledgement (ACK)

CSMA/CA also reduces collisions by using explicit packet acknowledgement (ACK)Receiving client must send back to sending

client an acknowledgement packet showing that packet arrived intact

If ACK frame is not received by sending client, data packet is transmitted again after random waiting time

Figure 6-16 illustrates CSMA/CA

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CSMA/CA

68

Point Coordination Function

Polling, an orderly channel access method, prevents collisions by requiring device to get permission before transmittingEach computer is asked in sequence if it wants

to transmit, as shown in Figure 6-18802.11b uses an optional polling function

known as Point Coordination Function (PCF)Beacon frame indicates how long PCF will be

used If client has nothing to transmit, it returns a null

data frame

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Polling

70

Association and Reassociation

MAC layer uses association and reassociation to make sure client joins WLAN and stays connectedUses either active or passive scanning process

Passive scanning has client listen for signal containing AP’s Service Set Identifier (SSID

Active scanning has client send out probe frame and wait for probe response frame from AP

After locating AP, client sends associate request frame and may join network after receiving frame with status code and client ID number

71

Reassociation

Reassociation involves dropping connection with one access point and establishing connection with another APAllows mobile clients to roam beyond coverage

area of single APAllows client to find new AP if original one

becomes weak or has interferenceClient scans to find new AP and sends

reassociation request frameNew AP then sends disassociation frame to

old AP as shown in Figure 6-19

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Reassociation Process

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MAC Frame Formats

802.11b specifies three different MAC frame formats Management frames—set up initial

communication between client and AP, as seen in Figure 6-21

Control frames—provide assistance in delivering frame that contains data, as seen in Figure 6-22

Data frames—carry information to be transmitted to destination client, as seen in Figure 6-23

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Management Frame

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Control Frame

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Data Frame

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High Speed WLANs

Three standards for high-speed WLANs that transmit at speeds over 15 MbpsIEEE 802.11aIEEE 802.11gHiperLAN/2

All WLANs are concerned with securityHow to prevent unauthorized access

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IEEE 802.11a

Approved in 1999, 802.11a transmits at speeds of 5.5 Mbps and 11 Mbps

Great demand for 802.11a WLANS, also called Wi-Fi5, with maximum speed of 54 MbpsDevices use gallium arsenide (GaAs) or silicon

germanium (SiGe) rather than CMOS semiconductors

Increased speed achieved by higher frequency, more transmission channels, multiplexing techniques, and more efficient error-correction

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Summary

Radio Frequency (RF) wireless local area networks (WLANs) have wide range of uses

Wireless NIC performs same functions as wired NIC, but it uses antenna to send and receive signals

Wireless NIC may be PCI (Peripheral Component Interface) expansion card for desktop PC, Type II PC Card for notebook computer, or Compact Flash (CF) Card for smaller device like PDA

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Summary

Access point (AP) contains three major partsAntennaRadio transmitter/receiverRJ-45 interface to connect by cable to standard

wired network by using special bridging software

AP has two basic functions Acts as base station for wireless networkActs as bridge between wireless and wired

networks

81

Summary

RF WLAN sends and receives data in two different modesAd hoc mode lets wireless clients communicate

among themselves without an access pointBasic Service Set (BSS) infrastructure mode

consists of wireless clients and at least one access point

Can add more access points to increase coverage area and create Extended Basic Service Set (ESS), consisting of two or more BSS wireless networks

82

Summary

HomeRF, also known as Shared Wireless Access Protocol (SWAP) defines how wireless devices such as computers and cordless phones can share and communicate around the homeHome RF version 1.0 products, introduced in

2000, transmit at 1.6 MbpsVersion 2.0, released in 2001, transmits at 10

Mbps

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Summary

IEEE 802.11 standard defines wireless network, either mobile or fixed, that transmits up to 2 MbpsMuch too slow for most network applications

IEEE 802.11b standard quickly became standard for wireless networks when it added two higher speeds: 5.5 Mbps and 11 Mbps

Physical Layer Convergence Procedure Standard (PLCP) for 802.11b uses direct sequence spread spectrum (DSSS)

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Summary

The PLCP reformats data from MAC layer into frame that PMD sublayer can transmit.

Frame has three parts: preamble, header, and data

802.11b uses Industrial, Scientific, and Medical (ISM) band for transmission at 11, 5.5, 2, or 1 Mbps

85

Summary

802.11b uses Distributed Coordination Function (DCF) access method that specifies a modified Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) procedureCDMA/CA makes all clients wait random

amount of time following collisionReduces collisions by using explicit packet

acknowledgements (ACK)

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Summary

MAC layer of 802.11b standard uses association and reassociation to allow client to join WLAN and stay connectedAssociation uses either passive or active

scanning to determines whether wireless client or access point should be accepted as part of network

Reassociation means client drops connection with one access point and reestablishes connection with another AP

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Summary

802.11b defines power management to conserve battery power without missing data transmissions

802.11b specifies three different types of MAC frame formatsManagement frames set up communications

between client and access pointControl frames assist in delivering data framesData frames carry information being transmitted

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Summary

802.11 standard defines three different interframe spaces (PFS) or time gapsRather than being “dead space,” these standard

spacing intervals or time gaps between transmission of data frames are used for special types of transmissions

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The Wireless Landscape

Wireless communication is standard means of communication for people in many occupations and circumstances

Table 1-1 summarizes wireless technologies, transmission distance, and speed

Figure 1-14 shows a wireless landscapeJob market to support wireless technology

is already exploding

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Wireless Technologies

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The Wireless Landscape

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Wireless Advantages and Disadvantages

AdvantagesMobilityEasier and less

expensive installation

Increased reliability

Disaster recovery

DisadvantagesHealth risks ?Radio signal

InterferenceSecurity

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Wireless Advantages

Mobility—employees have contact with network; work in teams for better productivity

Easier and less expensive installation—no need to install cables or modify historical property; easy to remodel office without concern for network access

Increased reliability—no outages caused by cable failure

Disaster recovery—easy to relocate office quickly using WLANs and laptop computers

94

Wireless Disadvantages

Health risks?—devices emit small levels of RFFDA—inconclusive about safety of wireless

devices FCC, FDA, and EPA set exposure guidelines for

wireless phones in 1996; Specific Absorption Rate (SAR) of no more than 1.6 watts per kilogram

Radio signal interference--other devices interfere Security—some wireless technologies add

security such as encryption or coded numbers for authorization to gain access to the network

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Wireless Performance Gap

WIDE AREA CIRCUIT SWITCHING

User Bit-Rate (kbps)

14.4digitalcellular

28.8 modem

ISDN

ATM

9.6 modem

2.4 modem2.4 cellular

32 kbps PCS

9.6 cellular

wired- wireless bit-rate "gap"

1970 200019901980YEAR

LOCAL AREA PACKET SWITCHING

User Bit-Rate (kbps)

Ethernet

FDDI

ATM100 M Ethernet

Polling

Packet Radio

1st genWLAN

2nd genWLAN

wired- wirelessbit-rate "gap"

1970 200019901980.01

.1

1

10

100

1000

10,000

100,000

YEAR

.01

.1

1

10

100

1000

10,000

100,000

96

Summary

Wireless communications, including Internet connections and networks, are becoming standard in business world

SWAP connects different devices for home usersQuickly becoming obselete

Bluetooth connects some devices over short distances

WLANs – WiFi 802.11 family

97

Summary

WLANS are fixture of business networksWLAN applications found in wide variety

of industries and organizationsPrimary advantage of WLAN is mobility

or freedom to move without being connected by a cable

Other advantages include easier and less expensive installation, increased network reliability, and support for disaster recovery