Transcript Guide to Wireless Communications

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
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
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 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
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 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 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
 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
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
Home Wireless Network
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 timesensitive transmissions
Version 1.0, introduced in 2000, transmits at
1.6 Mbps, but version 2.0, released in 2001, transmits at
10 Mbps
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
 The Bluetooth
headset
automatically
establishes a
connection
with the telephone
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
Bluetooth Network
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
 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
Many challenges face Bluetooth
Cost
Limited support
Shortcomings in protocol itself
Positioning in marketplace
Conflicts with other devices in radio spectrum
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
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
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
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
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)
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 Warehouse Network
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
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)
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
Access Point and Wireless NIC
Office WLAN
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
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 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
 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
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
Access Point as a Bridge
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 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
Ad Hoc 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
Extended Service Set (ESS)
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
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
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
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
WLAN features in PHY and MAC layers
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
Wireless changes to layers
Physical
Data Link
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
PHY Sublayers
PLCP Sublayer
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
PLCP Frame
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
802.11b ISM Channels
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
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
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
Collision
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
CSMA/CD
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)
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
CSMA/CA
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
Polling
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 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
Reassociation Process
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
Management Frame
Control Frame
Data Frame
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
 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
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
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
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
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
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)
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
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)
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
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
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
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 Technologies
The Wireless Landscape
Wireless Advantages and Disadvantages
Advantages
Mobility
Easier and less
expensive
installation
Increased
reliability
Disaster recovery
Disadvantages
Health risks ?
Radio signal
Interference
Security
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
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
100 M
Ethernet
100,000
10,000
FDDI
Ethernet
1000
100
User
Bit-Rate
(kbps)
WIDE AREA CIRCUIT SWITCHING
ATM
10,000
wired- wireless
bit-rate "gap"
1000
1st gen
WLAN
Polling
2nd gen
WLAN
Packet
Radio
ISDN
wired- wireless
bit-rate "gap"
28.8 modem
9.6 modem
9.6 cellular
2.4 modem
1
2.4 cellular
14.4
digital
cellular
32 kbps
PCS
.1
.1
.01
100
User
Bit-Rate
(kbps)
10
10
1
ATM
100,000
1970
1980
YEAR
1990
2000
.01
1970
1980
YEAR
1990
2000
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
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