Title: Guide to Wireless Communications
1Guide to Wireless Communications
2Objectives
- 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
3Wireless 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
4How 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
5Wireless Applications
- Wireless applications are found anywhere
employees need mobility, including in the
following industries - Education
- Military
- Business
- Entertainment
- Travel
- Construction
- Warehouse management
- Health care
6Wireless Communications in Industries
- Educationclassrooms, presentations, libraries,
access anywhere on campus - MilitaryUniversal Handset, a 1.5 lb. device
allows full motion video, cellular and satellite
communications, and Internet access - Businessoffice space where traditional
infrastructure does not exist, such as conference
room or hotel room
7Wireless Communications in Industries
- Entertainmentbarcodes on tickets validated by
handheld readers fans accessing game statistics,
watching replays, ordering concessions through
notebook computers or PDAs - Travelglobal positioning systems (GPS) providing
emergency roadside assistance airline passengers
using wireless notebooks or PDAs
8Wireless Communications in Industries
- Constructionscheduling construction phases and
employee travel, completing payroll, diagnosing
equipment - Warehouse Managementinventory, shipping, reading
bar-coded pallet labels - Health Caretracking dispensed medicine,
verifying patients bar-coded armbands, accessing
patient records
9Current 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
10SWAP
- 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
11Home Wireless Network
12HomeRF
- 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
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14Bluetooth
- 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
15Bluetooth Headset
- The Bluetooth headset automatically establishes a
connection with the telephone
16Piconet
- 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
17Bluetooth Network
18Network 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.
19Piconets
- 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
20Bluetooth Issues
- Many challenges face Bluetooth
- Cost
- Limited support
- Shortcomings in protocol itself
- Positioning in marketplace
- Conflicts with other devices in radio spectrum
21Cost
- 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
22Limited 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
23Protocol 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
24Market 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
25Spectrum 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
26Wireless 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
27WLAN Warehouse Network
28WLAN 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
29How 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)
30Wireless 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
31Access Point and Wireless NIC
32Office WLAN
33Wireless 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
34Integrated 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
35Software 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
36Access 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
37Access Point
38Functions 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
39Access Point as a Bridge
40Characteristics 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
41Ad 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
42Ad Hoc Mode
43Infrastructure 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
44Extended Service Set (ESS)
45Features 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
46ESS 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
47Wireless 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
48IEEE 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
49WLAN features in PHY and MAC layers
50IEEE 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
51Wireless changes to layers
52Physical 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
53PHY Sublayers
54PLCP Sublayer
55Physical 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
56PLCP Frame
57Physical Medium Dependent Standards
- Frame created by PLCP passes to PMD sublayer
where binary 1s and 0s 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
58802.11b ISM Channels
59Medium 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
60Two 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
61Distributed 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
62Collision
63CSMA/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
64CSMA/CD
65Distributed 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
66Packet 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
67CSMA/CA
68Point 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
69Polling
70Association 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 APs 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
71Reassociation
- 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
72Reassociation Process
73MAC Frame Formats
- 802.11b specifies three different MAC frame
formats - Management framesset up initial communication
between client and AP, as seen in Figure 6-21 - Control framesprovide assistance in delivering
frame that contains data, as seen in Figure 6-22 - Data framescarry information to be transmitted
to destination client, as seen in Figure 6-23
74Management Frame
75Control Frame
76Data Frame
77High 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
78IEEE 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
79Summary
- 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
80Summary
- 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
81Summary
- 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
82Summary
- 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
83Summary
- 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)
84Summary
- 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
85Summary
- 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)
86Summary
- 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
87Summary
- 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
88Summary
- 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
89The 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
90Wireless Technologies
91The Wireless Landscape
92Wireless Advantages and Disadvantages
- Advantages
- Mobility
- Easier and less expensive installation
- Increased reliability
- Disaster recovery
- Disadvantages
- Health risks ?
- Radio signal Interference
- Security
93Wireless Advantages
- Mobilityemployees have contact with network
work in teams for better productivity - Easier and less expensive installationno need to
install cables or modify historical property
easy to remodel office without concern for
network access - Increased reliabilityno outages caused by cable
failure - Disaster recoveryeasy to relocate office quickly
using WLANs and laptop computers
94Wireless Disadvantages
- Health risks?devices emit small levels of RF
- FDAinconclusive 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 - Securitysome wireless technologies add security
such as encryption or coded numbers for
authorization to gain access to the network
95Wireless Performance Gap
96Summary
- 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
97Summary
- 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