Transcript Chapter_5 - Eastern Illinois University

CHAPTER
Section A Network Building Blocks
PARSONS/OJA
5
Internet and
LAN
Technology
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Transmitting Data: Is it easy to transmit
data?
 A communications network is a collection of
computers and other devices that communicate
to share data, hardware and software
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What kind of coding process happens
on a communication network?
 Computers use several coding schemes based
on binary digits
 ASCII
 EBCDIC
 Unicode
 Binary numbers
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Exactly what is transmitted when I send
a message?
 When data is transmitted, it usually takes the
form of an electromagnetic signal
 On a communication network, your data may be
converted into several different types of waves
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Exactly what is transmitted when I send
a message?
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Network Links: How do signals travel
over a network?
 Data can travel from one network device to
another over a cable or through the air
 A communications channel is a physical path or
a frequency for a signal frequency
 Networks use different types of cables
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How do signals travel over a network?
 Today’s networks use twisted-pair cables
 UTP (unshielded twisted pair)
 STP (shielded twisted pair)
 looks similar to telephone cable
 has square plastic RJ-45 connector
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How do signals travel over a network?
 Another option is coaxial cable
 resembles cable-TV cable
 round, silver BNC connector
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How do signals travel over a network?
 Fiber-optic cable is a bundle of extremely thin
tubes of glass
 Each optical fiber (tube) is thinner than a
human hair
 Consists of strong inner support wire, multiple
strands of optical fiber and a tough outer cable
 Transmit pulses of light
 Data can also travel airways in form of RF
signals sent and received by a transceiver
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How do signals travel over a network?
 Microwaves provide another option for
transporting data
 Radio and microwave transmissions are bent
around the surface of the earth to reach towers
 Communications satellites play an important
part in long-distance communications
 A transponder on the satellite receives the
signal, amplifies it, and retransmits the signal
back to a ground station
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How do signals travel over a network?
 Infrared light can also carry data signals, but for
short distances with a clear line of sight
 Best for transmitting between notebook
computers and a printer, or between a PDA
and a desktop computer
 Laser light can also carry data signals, for a
longer distance, but requires a clear line of sight
 Experimental, but possibly may be useful for
transmitting data between buildings
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What’s bandwidth?
 Bandwidth is the transmission capacity of a
communications channel
 High-bandwidth communications systems, such
as cable TV, are sometimes referred to as
broadband
 Systems with less capacity, such as the
telephone system, are referred to as
narrowband
 The bandwidth of a digital channel is usually
measured in bits per second (bps)
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Network Devices: What kind of equipment
populates data communications networks?
 Each device that is connected to a network is
referred to as a node
 The term workstation usually refers to a
personal computer connected to a local area
network (LAN), it is also called a client
 A modem is a device that converts signals from a
computer into a signal that can travel over a wide
area network
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What kind of equipment populates data
communications networks?
 A network interface card (NIC) is the key
hardware component for connecting a computer
to a local area network.
 small circuit board that sends data to and from
workstation to network
 A server refers to any computer on a LAN or the
Internet that contains the software to manage and
process files for other network nodes
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What kind of equipment populates data
communications networks?
 A host computer usually refers to any computer that
provides services to network users
 A hub is a device that connects several nodes of a
LAN
 A router is a device that is connected to at least two
networks and makes decisions about the best route
for data
 A gateway is a device that performs functions similar
to a router
 A repeater amplifies and regenerates signals so they
can retain the strength to reach their destinations
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Network Addresses: How does data
find its destination?
 Every node on a network has an address
 Every packet of data that travels over a network
also has an address which helps to route a
packet to its destination
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Network Topology: Does a network require
a certain configuration of nodes?
 The layout of a network is referred to as its
physical topology
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Does a network require a certain
configuration of nodes?
 A real-world network can make use of more than
one topology
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Packet and Circuit Switching
Technology: What’s a packet?
 When you transmit data, it is broken up into small
pieces called packets
 A packet is a parcel of data that is sent across a
network
 Has the address of its sender
 Has the address of the destination
 Has some data
 When they reach the destination, they are put
back together into original form
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Why not just send an entire message?
 Engineers wanted a more robust communications
link for computer networks
 They devised packet switching in which a
message was divided into several packets that
can be routed independently to their destination
to avoid out-of-service or congested links
 Packet switching makes very efficient use of
available bandwidth and provides a steady
stream of data
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Communications Protocols: What is a
communications protocol?
 Communications protocol refers to set of rules
for transmitting data from one node to another
 Protocols allow two devices to negotiate and
agree on how data will be transmitted
 Scripts for dial-up modem
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How does a protocol initiate a
transmission?
 Protocols establish communications through
handshaking
 The devices decide on how to coordinate its
transmission
 Synchronous protocols are synchronized by a
signal called a clock when sending and receiving
data
 Asynchronous protocols require the
transmitting computer to send a start bit, then
data is sent, and a stop bit to mark the end of the
data
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Does data travel in both directions over
the same channel?
 Simplex – signal travels in only one direction
 Half duplex – signal travels in both directions,
but only one direction at a time
 Full duplex – signal travels in both directions at
the same time
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How does a protocol make sure that
data arrives without errors?
 Computers use error-checking protocols to make
ensure accurate delivery of data (such as over
the Internet)
 Parity bit – added to keep track of the number
of 1s and 0s
 Even parity protocol – requires number of 1s
to be an even number
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Network Classifications: How are
networks classified?
 Internetwork – a network composed of many
smaller networks
 Intranet – uses TCP/IP protocols but owned by a
private business and does not typically allow
remote access
 Extranet – similar to intranet except that it allows
remote password-protected access
 WAN – (wide area network) covers a large
geographical area and may consist of smaller
networks
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How are networks classified?
 LAN (local area network) – typically covers a very
limited geographical area
 Wireless network – uses radio frequencies
 HomeRF network – low-power wireless network
for home use
 HomePLC – uses building’s existing power line
cables
 HomePNA – uses existing telephone cables
 Novell – LAN that uses Novell Netware
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How are networks classified?
 Ethernet – free for all
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How are networks classified?
 Token Ring – connects
nodes in a physical star
configuration, but passes
data around a logical ring
using a technology called
a “token”.
 Wait for your turn…
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How are networks classified?
 Client/server – contains servers and clients
 Peer-to-peer (P2P) – every computer is
considered an equal
 KaZaa: file sharing among peers
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Background: How did the Internet get
started?
 The United States created ARPA (Advanced
Research Projects Agency).
 to help scientists communicate and share
valuable computer resources
 in response to the Soviet Union’s launch of
Sputnik in 1957, the first artificial satellite
 The ARPANET, created in 1969, connected
computers at four universities
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How did the Internet get started?
 In early 1990s, software developers created new
user-friendly Internet access tools
 Web browser: created at the University of
Illinois
 Today, the Internet connects computers all over
the globe and supplies information to people of
all ages and interests
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Internet Hardware and Connections: What type
of hardware populates Internet nodes?
 Difficult to diagram due
to over 100 million
nodes and 350 million
users
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What kinds of network devices are part
of an ISP?
 An ISP operates network devices that handle the
physical aspects of transmitting and receiving
data from your computer
 Modems
 Domain name server
 Router
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What kinds of network devices are part
of an ISP?
 An ISP links to other ISPs in a sort of ISP network
 Network service Providers (NSPs) supply ISPs
with access to high-speed transmission lines that
form the backbone of the Internet
 Interstate highways of the Internet
 NSPs also provide routers at network connection
points
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How fast does data travel over the
Internet?
 Using Ping or Traceroute, you can discover how
long data is in transit
 On average, data within the US usually arrives at
its destination 110-120 ms (milliseconds) after it
is sent
 Overseas transmission require a little more time
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Internet Protocols: Why does the
Internet use TCP/IP?
 TCP/IP provides a standard that is fairly easy to
implement, public, free, and extensible
 The Internet is not owned, operated, or controlled
by any single entity
 TCP/IP is glue that holds the Internet together
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How does TCP/IP work?
 It is a suite of protocols
 TCP (Transmission Control Protocol) – breaks
a message or file into packets
 IP (Internet Protocol) – responsible for
addressing packets so that they can be routed
to their destination
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Is TCP/IP the only Internet Protocol?
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IP Addresses: Does the Internet use a
special addressing scheme?
 The IP part of TCP/IP defines the format for the
addresses that identify computers on the Internet
 These addresses are called IP addresses
 An IP address is a series of numbers, such as
204.127.129.001
 It is separated into four sections by periods
 Each section’s number cannot exceed 255
 Each address requires 32 bits (8 bits per
section)
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Do I need a permanent IP address?
 Static IP address – permanently assigned IP
address
 Dynamic IP address – temporarily assigned
 ISPs need static IP addresses
 Clients typically use dynamic IP addresses as the
IP addressing scheme provides approximately
only 4.3 billion unique addresses
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Domain Names: What’s a domain
name?
 People find it difficult to remember long strings of
numbers, so host computers also have names
called domain names
 Domain name – “fully qualified domain name”
(FQDN), usually typed in all lowercase
 Key component of URLs and e-mail addresses
 www.thex-files.com/episode236 - www.thexfiles is the domain name
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What’s a domain name?
 A domain name ends with an extension that
indicates its top-level domain
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How are domain names related to IP
addresses?
 Each name corresponds
to an IP address
 Domain name system
– huge database that
houses the names and
IP addresses
 Domain name servers
– computers that house
the database
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Do I need my own domain name?
 Not for normal client-style Internet activities
 If you plan to operate your own Web server, you
may want a name
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How do I get a domain name?
 ICANN (Internet Corporation for Assigned Names
and Numbers) – global organization that
coordinates the technical management of the
Internet’s domain name system, allocation of IP
addresses, and the assignment of protocol
parameters
 Organizations or individuals can select a domain
name and register it by using an online
registration service
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How do I get a domain name?
Click to start
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Is a fee required to obtain a domain
name?
 You can register a domain name for a minimal
annual fee ($25 - $50)
 Some Internet entrepreneurs have registered
high-profile domain names and resell them
 Sell-videos.com - $35,000
 Thelocallistings.com - $87,500
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Section C Internet Access
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Dial-Up Connections: How does a dialup connection work?
 Uses POTS (plain old telephone service) to
transport data between your computer and your
ISP
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How does a dial-up connection work?
 While connected to your ISP, your call is routed
through the telephone company’s local switch to
the ISP
Local
Switch
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How does a modem work?
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Can I talk and send data at the same
time?
 When connected to ISP, data is transmitted in
same frequencies used for voice conversations
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How fast is a modem?
 Speed was measured as baud rate, number of
times per second that a signal in a
communications channel varies speeds
 Today, measure in terms of bits per second
 V.90 – theoretical maximum speed of 56 Kbps
 Even with perfect connection, a 56 Kbps modem
tops out at about 44 Kbps
 Downstream vs. upstream
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Cable Television Connections: How can the
cable TV system provide Internet access?
 Community antenna television – CATV
 The satellite dish farm at which television
broadcasts are received and retransmitted is
referred to as the head-end
 From the head-end, cabling system branches out
and eventually reaches consumers’ homes
 Topology is similar to computer network, and that
is what is formed when you use cable TV as your
ISP
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How can the cable TV system provide
Internet access?
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Are television and data signals carried
over the same cable?
 Lowest-capacity coaxial cable has far greater
capacity than POTS lines
 Cable’s bandwidth is divided among 3 activities
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How do I set up a cable modem
connection?
 Need an Ethernet NIC
 Need a cable modem,
which converts your
computer’s signal into
one that can travel over
CATV cable
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What’s the significance of becoming
part of a “neighborhood network”?
 With CATV, your computer becomes part of a
neighborhood data network
 More people on the network, means slower
service
 Also, in early days your network neighborhood
showed your neighbors
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What’s the significance of becoming
part of a “neighborhood network”?
 An always-on connection is always connected
 A hacker who discovers that your computer has a
security weakness can easily find it again, and its
high-speed access makes it a very desirable
target
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How do I secure an always-on
connection?
 Disable file and print sharing
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How do I secure an always-on
connection?
 Shut down your computer when you are not using
it
 Install personal firewall software, which is
designed to analyze and control incoming and
outgoing packets
 Pick level – high, medium, or low
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DSL, ISDN, T1, and T3: What other options are
available for high-speed Internet access?
 Several services such as DSL, ISDN, T1, and T3
take advantage of full capacity of the telephone
connections (normal dial-up services do not)
 Offers high-speed digital communications links
for voice and data
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What is DSL?
 DSL (Digital Subscriber Line) is a high-speed,
always-on, Internet access technology that runs
over standard phone lines
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What is DSL?
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What is DSL?
 Speed varies, but most are rated at 1.5 Mbps
downstream
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How do I install DSL?
 Telephone line
connected to DSL
switch at your house
 Line connected to
DSL modem which
connects to your
computer’s Ethernet
card
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Who uses T1 or T3 service?
 T1 – high-speed 1.544 Mbps digital network
 Consists of 24 individual channels (64 Kbps for
each)
 Popular for businesses and ISPs
 Not as fast as DSL
 T3
 672 channels
 Supports data rates of about 43 Mbps
 Sometimes referred to as DS3 (Digital Service-3)
lines
 Provide many of the links on the Internet backbone
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Wireless Internet Access: What are the options
for wireless connections to the Internet?
 Personal satellite connections – expensive, but
sometimes only option (particularly in remote
rural areas)
 Cellular telephones – slowest, but provides
mobile Internet access
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How does satellite access work?
 Direct satellite service (DSS) uses a
geosynchronous or low-earth satellite to send
television, voice, or computer data directly to a
satellite dish
 Two-way satellite service ships both upstream
and downstream data through the satellite
 offers 500 Kbps downstream
 40-60 Kbps upstream
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How does satellite access work?
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What’s the fastest Internet connection?
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LAN Services and Resources: What
sort of resources does a LAN provide?
 Main advantage of a LAN is that multiple users
can share a limited number of resources
 Can share a high-speed connection
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How do I access network resources?
 When you boot your computer, OS looks to see if
it can access a LAN
 Generally need to reboot after loosing network
connection
 The OS keeps track of network resources you
can access automatically
 Some network resources become available as
soon as your computer completes the boot
process, and others after you use your
networking utilities
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Can a LAN use existing phone or
electrical wiring?
 HomePNA uses a special NIC and cable to
connect each computer to a standard telephone
wall jack
 Network frequency is usually different from voice,
so can use network at same time you place a call
 You can not make a call when dial-up Internet
connection is active however
 HomePLC uses special NIC to connect to
standard electrical outlet, but power fluctuations
can adversely affect signal
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Can LANs use wireless technology?
 Wireless LANs are slower but eliminate unsightly
wires
 Signals can be disrupted by large metal objects,
cell phones, pagers, and other wireless devices
 Most popular s 802.11b
 11 Mbps, spans 300 feet, and can be used
with Ethernet networks
 Bluetooth
 200-400 Kbps, range of 35 feet
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LANs with wireless technology
 Wi-Fi: Wireless Fidelity:
 Avoid expense of wiring installation for network
 Enjoy mobility
 Up to 100 times faster than dial-up connection
• 11 mps
 Range of 100 up to 1,000 feet
 Signals operate in the 2.4 and 5Ghz
radio bands, which are also used today by many
cordless phones
 Hot spot operators
• Starbucks, hotels, airports, etc.
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