Transcript Personal Area Network

Communications, Networks, &
Safeguards
Chapter
6
6.1 From the Analog to the Digital Age
6.2 Networks
6.3 Wired Communications Media
6.4 Wireless Communications Media
6.5 Cyberthreats, Hackers, &
Safeguards
6.6 The Future of Communications
McGraw-Hill/Irwin
© 2007 The McGraw-Hill Companies, Inc. All rights reserved.
Networks
□ A system of interconnected
computers, telephones, or other
communications devices that can
communicate with one another and
share applications and data
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Networks
□ Before we had computer networks,
people used “sneakernet” to share
data between computers
◊ Person 1 saved their document to a
floppy disk
◊ Then they walked over to person 2’s desk
(wearing sneakers, of course) and
handed over the disk to person 2
◊ Person 2 loaded the disk into their
computer to read and edit the document
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Networks
□ Since the days of “sneakernet”, networks
have become standard. They enable us to
(benefits):
◊ Share peripheral devices such as laser
printers
◊ Share programs and data
◊ Use e-mail and other communication
programs
◊ Backup critical information because it is
stored centrally
◊ Access shared databases
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Types of Networks
Based on coverage scope
□ WAN – Wide Area Network
◊ Covers a wide geographic area, such as a country or the world
□ MAN – Metropolitan Area Network
◊ Covers a city or a suburb
□ LAN – Local Area Network
◊ Connects computers and devices in a limited geographic area
such as an office, building, or group of nearby buildings
□ HAN – Home Area Network
◊ Uses wired, cable, or wireless connections to link a household’s
digital devices
□ PAN – Personal Area Network
◊ Uses short-range wireless technology to connect an individual’s
personal electronics like cellphone, PDA, MP3 player, notebook
PC, and printer
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Types of Networks
Based on roles
□ Client/Server
□ Peer-to-Peer
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Types of Networks
Based on roles
□ Client/Server
◊ Consists of clients, which are computers that
request data, and servers, which are
computers that supply data
◊ File servers act like a network-based shared
disk drive
◊ Database servers store data but don’t store
programs
◊ Print servers connect one or more printers and
schedule and control print jobs
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◊ Mail servers manage email
Types of Networks
Based on roles
□ Peer-to-Peer
◊ All computers on the network
communicate directly with each other
without relying on a server
◊ Cheaper than client/server since servers are
typically more expensive than PCs
◊ There are often problems with knowing who
has the current version of documents and
files
◊ Too slow for use in larger offices
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Types of Networks
Based on roles
□ Legal considerations
◊ Downloading copyrighted material without
paying violates U.S. copyright laws
◊ Server-based online file sharing sites such as
Napster have been shut down
◊ Peer-to-Peer file-sharing sites such as Kazaa,
Grokster, and Gnutella have been more
difficult to control. Why?
◊ What are publishers doing against this
problem?
Watch out!
Don’t download illegally!
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Networks
Intranets, Extranets, VPNs
□ Intranets
◊ An organization’s private network that uses
the infrastructure and standards of the
internet and the web
□ Extranets
◊ Private networks that connect not only internal
personnel but also selected suppliers and other
strategic parties
□ Virtual Private Networks
◊ Private networks that use a public network,
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usually the internet, to connect remote sites
Networks
Components
□ Hosts & Nodes
◊ Host: the central computer that controls
the network
◊ Node: a device that is attached to the
network
□ Packets
◊ The format for sending electronic
messages
◊ A fixed-length block of data for
transmission
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Network
Components
□ Protocols
◊ The set of conventions governing the exchange
of data between hardware and/or software
components in a communications network
◊ Built into the hardware or software you are using
◊ Govern the packet design and transmission
standards
◊ Examples are:
◊
◊
◊
◊
◊
TCP/IP for LANs and internet
AppleTalk for older Mac networks
SIP for Voice over IP (VoIP)
CDMA for cellphones
IPX for older Novell networks
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Network
Packets
□ TCP/IP Packets carry four types of
information
1. Sender’s address (source IP
number)
2. Address of intended recipient
(destination IP number)
3. Number of packets the original
data was broken into
4. Packet number and sequence info
for each packet
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Network
Packets
□
TCP/IP Packets carry four types of information
3. Number of packets the original data was broken
into
◊ This happens because the amount of data the PC is
sending can be much larger than the space in a single
packet
◊ So the data has to get broken up in one or more packets
◊ Then the packets have to be assigned a number like 1 of
6, 2 of 6, 3 of 6, 4 of 6, 5 of 6, and 6 of 6
4. Packet number and sequence info for each packet
◊ Packets may arrive out of order (1, 6, 3, 2, 5, 4 for
example)
◊ This information is used to resequence the packets and
put them back in the correct order (1, 2, 3, 4, 5, 6) so
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they can be read
Network
Topologies
□ Bus – all nodes are connected to a single wire or
cable
□ Ring – all nodes are connected in a continuous
loop
□ Star – all nodes are connected through a central
host
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Network
Packet Collision Schemes
□ Collisions happen when two data
packets are going opposite directions
on shared media
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Network
Packet Collision Schemes
□ Ethernet – deals with collisions
◊ All devices send data at once
◊ Collisions happen regularly
◊ Data is simply resent until it arrives
□ Token ring – avoids collisions
◊ Devices take turns sending data
◊ Token is sent around the ring
◊ Wait to get the token, then send data
$$$
Pricier than Ethernet
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Network
Devices
□ Daisy Chain:
◊ Used in peer-to-peer networks – direct
connections from one PC to the next
□ Hub:
◊ Used in small LANs to connect PCs and
LAN segments to each other. Forwards
to all ports
□ Switch:
◊ Used in larger, busy LANs – faster than
hubs because it forwards only to
correct destination
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Network
Devices
□ Bridge:
◊ Used to connect two networks of the same type
□ Gateway:
◊ Connects two networks of different types
□ Router:
◊ Connects multiple LANs together. Routers are
the internet backbone
□ Backbone:
◊ The main route that connects all the gateways,
routers, and other computers in an organization
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Network
Devices
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Networks
Components
□ Connections
◊ Wired – twisted-pair, coaxial cable, or
fiber-optic
◊ Wireless – infrared, microwave
(Bluetooth), broadcast (Wi-Fi) or satellite
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Wired Communications Media
□ Communications media carry signals over
a communications path
◊ Twisted-Pair Wire
◊ 2 strands of insulated copper wire twisted around each
other
◊ Twisting reduces interference (crosstalk) from
electrical signals
◊ Data rates are 1 – 128 Megabits per second
◊ Coaxial Cable
◊ Insulated copper wire wrapped in a metal shield and
then in an external plastic cover
◊ Used for cable TV and cable internet electric signals
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◊ Carries voice and data up to 200 megabits per second
Wired Communications Media
□ Communications media continued
◊ Fiber-optic cable
◊ Dozens or hundreds of thin strands of glass
or plastic that transmit beams of light, not
electricity
◊ Can transmit up to 2 gigabits per second
◊ More expensive than twisted-pair or coax
◊ Lighter and more durable than twisted-pair or
coax
◊ More difficult to tap into than twisted-pair or
coax
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Wired Communications Media
for the home
□ Ethernet
◊ Pull Cat5 cables through the house (yourself or
contractor)
◊ Connect to PC’s Ethernet network interface card (nic)
◊ For several PCs, get a hub or switch to connect them all
◊ 10 or 100 megabits per second
□ HomePNA
◊ Uses existing telephone wiring and jacks
◊ Requires HomePNA nic in your PC
◊ Speeds of 10 – 240 megabits per second
□ Homeplug
◊ Uses existing home electrical lines
◊ Speeds of 14 megabits per second
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Wireless Communications Media
□ Electromagnetic spectrum of radiation is the
basis of all telecommunications signals
◊ Includes the longest radio waves (9 kHz) and audio
waves (sound), up through gamma rays that come from
nuclear decay (thousands of gigahertz)
◊ Radio-frequency spectrum is the part of the
electromagnetic spectrum that we use for radio
communication
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Wireless Communications Media
Bandwidth
□ Narrowband (or Voiceband)
◊ Used for regular telephone communications
◊ Transmission rate < 100 kilobits per second
□ Medium Band
◊ Used for long-distance data transmission or to
connect mainframe and midrange computers
◊ Transmission rate 100 kb to 1 megabit per second
□ Broadband
◊ For high-speed data and high-quality audio and
video
◊ Transmission rate 1 megabit per second to 100
megabits per second
□ US households get 4 – 5 MB while Japanese get
100 MB per second
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Wireless Communications Media
□ Infrared Transmission
◊ Sends signals using infrared light
◊ Frequencies are too low to see (1-4 Mbits per
second)
□ Broadcast Radio
◊ AM/FM, CB, ham, cellphones, police radio
◊ Sends data over long distances using a transmitter
and a receiver
□ Microwave Radio
◊ Superhigh frequency radio waves (1 gigahertz)
◊ Requires line-of-sight transmitters and receivers
□ Communications Satellites
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Wireless Communications Media
□ Communications Satellites
◊ These are microwave relay stations in orbit around the
earth - Uplinking: transmitting a signal from ground station to a satellite
◊ Cover broad service area
◊ Cost $300 million to $700 million each + launch costs
◊ Can be placed at different heights: GEO, MEO, LEO
◊ GEO – geostationary earth orbit
◊
◊
22,300 miles up above earth
Always above equator
◊ MEO – medium-earth orbit
◊
5,000 – 10,000 miles up
MEO
◊ LEO – low-earth orbit
◊
◊
GEO
200 – 1,000 miles up
Has less signal delay than GEO, MEO satellites
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LEO
Wireless Technologies
□
Global Positioning System (GPS):
◊ Launched by the military in the 80s and used
extensively during the Gulf War
◊ Incorporates 27 earth-orbiting satellites
continuously transmitting timed radio signals that
can be used to identity locations
◊ Uses the concept of Triangulation to find locations
given the transmitted signals
◊ Accurate within 3-50ft
◊ Uses and limitations of GPS
1
1
Possible location
given one signal
1
2
Possible location
given two signals
Concept of Triangulation
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Possible location
given three signals
2
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Wireless Communications Media
Long-Distance Wireless
□ Two-way pagers: Blackberry and Treo
□ 1G: First Generation Cellular
◊ Analog cellphones
◊ Designed for voice communication using a
system of hexagonal ground-area cells
around transmitter-receiver cell towers
◊ Good for voice – less effective for data due to
handing off
□ 2G: Second Generation Cellular
◊ Use same network of cell towers to send voice
and data in digital form over the airwaves
◊ Required digital receivers on original analog
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celltowers
Wireless Communications Media
2G Wireless
□ There are two competing, incompatible
standards
◊ CDMA – Code Division Multiple Access
◊ Transmission rates 14.4 kilobits per second
◊ Used by Verizon and Sprint
◊ GSM – Global System for Mobile
Communications
◊ Transmission rates of 9.6 kilobits per second
◊ Used by Cingular and T-Mobile, as well as Western
Europe, Middle East and Asia
◊ US GSM and European GSM use different
frequencies
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Wireless Communications Media
2.5G Wireless
□ Data speeds of 300–100 kilobits per
second
◊ GPRS – General Packet Radio Service
◊ An upgrade to 2.5G
◊ Speeds of 30 – 50 kilobits per second
◊ EDGE is Enhanced Data for Global
Evolution
◊ A different 2.5G upgrade
◊ Speeds of up to 236 kilobits per second
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Wireless Communications Media
3G Wireless
□ Third generation wireless (SmartPhones)
◊ High speed data: 144 kilobits per second up
to 2 megabits per second
Discussion
◊ Accept e-mail with attachments
Question: If
◊ Display color video and still pictures your cellphone
can download
◊ Play music
and play music,
◊ Two important upgrades:
do you still
◊ EV-DO – Evolution Data Only
need an i-pod?
◊ Average speeds of 400 – 700 kilobits per second,
peaks of 2 megabits per second
◊ UMTS – Universal Mobile Telecommunications
System
◊ Average speed of 220 – 320 kilobits per second
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Wireless Communications Media
Short-range Wireless
□ Wi-Fi (802.11) networks
◊ Wi-Fi b, a, and g correspond to 802.11b, 802.11a, and
802.11g (protocols)
◊ 802.11 is an IEEE wireless technical specification
◊ 802.11b is older, transmits 11 megabits per second
◊ 802.11a is faster than b but with weaker security than g
◊ 802.11g is 54 megabits per second and transmits 50 ft
◊ Wi-Fi n with MIMO extends range of Wi-Fi using multiple
transmitting and receiving antennas – 200 megabits per
second for up to 150 ft
□ Warning! Security is disabled by default on Wi-Fi
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Wireless Communications Media
Personal Area Wireless
□ Bluetooth
◊ Short-range wireless standard to link cellphones,
PDAs, computers, and peripherals at distances up
to 30 ft
◊ Named after King Harald Bluetooth, the Viking who
unified Denmark and Norway
◊ Transmits 720 kilobits per second
◊ When Bluetooth devices come into range of each
other, they negotiate. If they have information to
exchange, they form a temporary wireless network
◊ Bluetooth can also be used to eavesdrop on
networks
◊ Turn it off on your cellphone unless you need it at
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that time