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Guide to Wireless Communications 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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objectives
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
wireless the hype
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
how wireless technology is used
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
wireless applications
Wireless Applications
  • Wireless applications are found anywhere employees need mobility, including in the following industries:
    • Education
    • Military
    • Business
    • Entertainment
    • Travel
    • Construction
    • Warehouse management
    • Health care
wireless communications in industries
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
wireless communications in industries7
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
wireless communications in industries8
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
current wireless systems
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
slide10
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
homerf
HomeRF
  • Shared Wireless Access Protocol (SWAP), Home RF is an open industry specification that allows wireless devices to share information around home
    • Operates in license-free 2.4 GHz frequency and uses frequency-hopping spread spectrum (FHSS)
    • Provides quality-of-service (QoS) that prioritizes time-sensitive transmissions
    • Version 1.0, introduced in 2000, transmits at 1.6 Mbps, but version 2.0, released in 2001, transmits at 10 Mbps
bluetooth
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
bluetooth headset
Bluetooth Headset
  • The Bluetooth headset automatically establishes a connection with the telephone
piconet
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

network topology
Network Topology
  • Two types of Bluetooth network topologies
    • Piconet
    • Scatternet (collection of piconets)
  • Two Bluetooth devices within range automatically connect
    • One device is the master, controlling all wireless traffic
    • The other is the slave, taking commands from the master.
piconets
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
bluetooth issues
Bluetooth Issues
  • Many challenges face Bluetooth
    • Cost
    • Limited support
    • Shortcomings in protocol itself
    • Positioning in marketplace
    • Conflicts with other devices in radio spectrum
slide21
Cost
  • Chips have decreased in price to about $15 from a high of over $75
    • Not advantageous to replace a $7 cable with a $15 chip
    • Many think cost must come down to about $5 before Bluetooth reaches competitive advantage
limited support
Limited Support
  • Bluetooth is caught in “chicken or egg” scenario
    • Because 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
protocol limitations
Protocol Limitations
  • Major limitation is no hand-off between piconets
    • Unlike 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
market position
Market Position
  • Current position is between IEEE 802.11x WLANs and cell phones
    • WLAN is preferred technology for connecting wireless devices to form network
    • WLAN is mature, robust, flexible, popular technology
    • Trend today is fewer devices instead of more, and cell phones have integrated capabilities that Bluetooth lacks
spectrum conflict
Spectrum Conflict
  • The 2.4 GHz band that Bluetooth uses conflicts with IEEE 802.11b WLANs
    • WLAN may drop connection when detects another device sharing its frequency
    • Most obvious fix is moving Bluetooth device away from WLAN
    • Many vendors offer products that let Bluetooth and 802.11b WLANs share spectrum
    • New 802.11a WLAN standard uses a different frequency, eliminating the conflict
wireless local area network wlan
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
wlan applications
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
how wlans operate
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 network
    • Wireless network interface (NIC) cards
    • Access points (AP)
wireless nic and access point ap
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 LAN
    • Figure 1-9 shows an AP and wireless NIC
  • WLANs also used in office environments, as shown in Figure 1-10
wireless network interface card
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 signals
    • NIC changes internal data from parallel to serial, divides data into packets with sending and receiving addresses, determines when to send packet, and transmits packet
integrated wireless nics
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 display
    • This will keep RF waves away from motherboard
software for wireless nics
Software for Wireless NICs
  • Software may be part of operating system itself
    • Windows XP has software integrated while previous versions of Windows do not
  • Software may be separate program loaded into the computer
    • All operating systems before Windows XP, including Linux, require loading software
    • Operating systems for PDAs may soon integrate software to recognize a wireless NIC
access point
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
functions of an access point
Functions of an Access Point
  • Access point has two basic functions
    • Acts as base station for wireless network
    • Acts as bridge between wireless and wired network
    • Bridges are LAN connectors at MAC level
  • See Figure 6-7
characteristics of an access point
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 problem
    • Power over Ethernet feature delivers DC power through standard unshielded twisted pair (UTP) Ethernet cable
ad hoc mode
Ad Hoc Mode
  • Ad Hoc Mode or peer-to-peer mode lets wireless clients communicate among themselves without an access point
    • Officially 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
infrastructure mode
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
features of access points
Features of Access Points
  • Coverage area should overlap when using multiple access points
    • Wireless clients survey radio frequencies to find an AP that provides better service
    • A seamless handoff occurs when client associates with new AP
ess and subdivided networks
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 freely
    • Alternative may be software that tricks network into seeing subnets as one network
wireless gateway
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
ieee 802 11
IEEE 802.11
  • Introduced in 1990
  • Defines 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 features
    • See Figure 6-10
  • Slow bandwidth insufficient for most network applications
ieee 802 11b
IEEE 802.11b
  • 1999 amendment to 802.11 standard
  • Added two higher speeds: 5.5 and 11 Mbps
  • Called Wi-Fi
  • Quickly became standard for WLANs
physical layer
Physical Layer
  • Physical layer that sends and receives signals from network is divided into two parts
    • See 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 transmit
    • Listens to determine when data can be sent
physical layer convergence procedure standards
Physical Layer Convergence Procedure Standards
  • Based on direct sequence spread spectrum (DSSS)
  • Reformats data from MAC layer into frame that PMD sublayer can transmit
    • See Figure 6-13
  • Frame has three parts
    • Preamble and Header transmit at 1 Mbps
    • Data portion, containing from 1 to 16,384 bits, may be sent at faster rate
physical medium dependent standards
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 transmissions
    • May use 14 frequencies, beginning at 2.412 GHz and incrementing in .005 GHz steps
    • See Table 6-1
medium access control layer changes
Medium Access Control Layer Changes
  • 802.11 Data Link layer has two sublayers
    • Logical 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
two kinds of coordination
Two Kinds of Coordination
  • Coordination necessary among devices sharing same RF spectrum
  • Two kinds of coordination
    • Distributed coordination function is 802.11b standard
    • Point coordination function is optional
distributed coordination function
Distributed Coordination Function
  • Channel access methods refer to different ways of sharing
  • Contention
    • Computers compete for use of network
    • May cause collisions that result in scrambled messages, as seen in Figure 6-14
    • Must first listen to be sure no other device is transmitting
csma cd
CSMA/CD
  • 802.3 Ethernet standard uses contention with “listening” as channel access method
    • Carrier 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
distributed coordination function dcf
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 clear
    • This technique helps reduce collisions
packet acknowledgement ack
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
point coordination function
Point Coordination Function
  • Polling, an orderly channel access method, prevents collisions by requiring device to get permission before transmitting
    • Each computer is asked in sequence if it wants to transmit, as shown in Figure 6-18
  • 802.11b 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
association and reassociation
Association and Reassociation
  • MAC layer uses association and reassociation to make sure client joins WLAN and stays connected
    • Uses 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
reassociation
Reassociation
  • Reassociation involves dropping connection with one access point and establishing connection with another AP
    • Allows mobile clients to roam beyond coverage area of single AP
    • Allows client to find new AP if original one becomes weak or has interference
  • Client scans to find new AP and sends reassociation request frame
    • New AP then sends disassociation frame to old AP as shown in Figure 6-19
mac frame formats
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
high speed wlans
High Speed WLANs
  • Three standards for high-speed WLANs that transmit at speeds over 15 Mbps
    • IEEE 802.11a
    • IEEE 802.11g
    • HiperLAN/2
  • All WLANs are concerned with security
    • How to prevent unauthorized access
ieee 802 11a
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 Mbps
    • Devices 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
summary
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
summary80
Summary
  • Access point (AP) contains three major parts
    • Antenna
    • Radio transmitter/receiver
    • RJ-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 network
    • Acts as bridge between wireless and wired networks
summary81
Summary
  • RF WLAN sends and receives data in two different modes
    • Ad hoc mode lets wireless clients communicate among themselves without an access point
    • Basic 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
summary82
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 home
    • Home RF version 1.0 products, introduced in 2000, transmit at 1.6 Mbps
    • Version 2.0, released in 2001, transmits at 10 Mbps
summary83
Summary
  • IEEE 802.11 standard defines wireless network, either mobile or fixed, that transmits up to 2 Mbps
    • Much 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)
summary84
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
summary85
Summary
  • 802.11b uses Distributed Coordination Function (DCF) access method that specifies a modified Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) procedure
    • CDMA/CA makes all clients wait random amount of time following collision
    • Reduces collisions by using explicit packet acknowledgements (ACK)
summary86
Summary
  • MAC layer of 802.11b standard uses association and reassociation to allow client to join WLAN and stay connected
    • Association 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
summary87
Summary
  • 802.11b defines power management to conserve battery power without missing data transmissions
  • 802.11b specifies three different types of MAC frame formats
    • Management frames set up communications between client and access point
    • Control frames assist in delivering data frames
    • Data frames carry information being transmitted
summary88
Summary
  • 802.11 standard defines three different interframe spaces (PFS) or time gaps
    • Rather than being “dead space,” these standard spacing intervals or time gaps between transmission of data frames are used for special types of transmissions
the wireless landscape
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 landscape
  • Job market to support wireless technology is already exploding
wireless advantages and disadvantages
Advantages

Mobility

Easier and less expensive installation

Increased reliability

Disaster recovery

Disadvantages

Health risks ?

Radio signal Interference

Security

Wireless Advantages and Disadvantages
wireless advantages
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
wireless disadvantages
Wireless Disadvantages
  • Health risks?—devices emit small levels of RF
    • FDA—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
wireless performance gap

LOCAL AREA PACKET SWITCHING

WIDE AREA CIRCUIT SWITCHING

ATM

ATM

100 M

100,000

100,000

Ethernet

10,000

10,000

FDDI

wired- wireless

bit-rate "gap"

Ethernet

wired- wireless

User

User

1000

1000

bit-rate "gap"

ISDN

Bit-Rate

Bit-Rate

2nd gen

WLAN

(kbps)

(kbps)

100

100

28.8 modem

1st gen

WLAN

32 kbps

Polling

9.6 modem

PCS

14.4

digital

cellular

10

10

9.6 cellular

2.4 modem

Packet

2.4 cellular

1

1

Radio

.1

.1

.01

.01

1970

1980

1990

2000

1970

1980

1990

2000

YEAR

YEAR

Wireless Performance Gap
summary96
Summary
  • Wireless communications, including Internet connections and networks, are becoming standard in business world
  • SWAP connects different devices for home users
    • Quickly becoming obselete
  • Bluetooth connects some devices over short distances
  • WLANs – WiFi 802.11 family
summary97
Summary
  • WLANS are fixture of business networks
  • WLAN applications found in wide variety of industries and organizations
  • Primary 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