Guide to Wireless Communications
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
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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
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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
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Wireless Applications
Wireless applications are found anywhere employees need mobility, including in the following industries:EducationMilitaryBusiness EntertainmentTravelConstructionWarehouse managementHealth care
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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
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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
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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
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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
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Home Wireless Network
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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
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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
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Bluetooth Headset
The Bluetooth headset automatically establishes a connection with the telephone
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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
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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.
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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
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Bluetooth Issues
Many challenges face BluetoothCostLimited supportShortcomings in protocol itselfPositioning in marketplaceConflicts with other devices in radio spectrum
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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
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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
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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
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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
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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
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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
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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
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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)
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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
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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
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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
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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
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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
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Access Point as a Bridge
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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
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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
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Ad Hoc Mode
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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
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Extended Service Set (ESS)
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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
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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
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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
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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
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WLAN features in PHY and MAC layers
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IEEE 802.11b
1999 amendment to 802.11 standardAdded two higher speeds: 5.5 and 11 MbpsCalled Wi-FiQuickly became standard for WLANs
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Wireless changes to layers
PhysicalData Link
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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
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PHY Sublayers
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PLCP Sublayer
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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
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PLCP Frame
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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
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802.11b ISM Channels
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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