Matakuliah
Tahun
Versi
: T0604-Pengantar Teknologi Informasi
: 2008
: 2.0/0.0
Pertemuan 13
Komunikasi, Jaringan, &
Pengamanannya
Sumber:
Chapter 6. Communications,
Networks, & Safeguards, p.309
Williams, B.K, Stacy C. Sawyer (2007).
Using Information Technology: A
Practical Introduction to Computers &
Communications. Seventh Edition,
McGraw-Hill, New York. ISBN-13: 978-007-110768-6
1
Learning Outcomes
Pada akhir pertemuan ini, diharapkan mahasiswa
akan mampu :
• menjelaskan pengertian komunikasi/
telekomunikasi, dan jaringan; perbedaan
antara data analog dan digital; jenis-jenis
media komunikasi (C2)
2
Outline Materi
• From the Analog to the Digital Age
• Networks
• Wired Communications Media
3
From the Analog to the
Digital Age
• Analog signals use variation
of a wave form to send
information
• The wave forms look like the
sine wave shown at right
• In FM signals the Frequency
is varied (Modulated)
• In AM signals the Amplitude
is varied (Modulated)
• Radios send signals this way
• Light works this way
• Hearing and phones work
this way
• Modems work this way
Sine Wave
1
0.5
0
Amplitude
-0.5
-1
S1
Frequency
6-4
From the Analog to the
Digital Age
Digital Signal
1
Time
6-5
41
37
33
29
25
21
17
13
9
0
5
Data
1
• Digital signals send data in terms
of 1s and 0s
• A digital signal may look like this
one at right
• Notice how the signal goes up
and down abruptly because the
only values that matter are 0 and
1 and the timing of when they
occur
• Computers use digital signals
• Newspaper photographs are
digital since they are made up of
little dots
S1
From the Analog to the
Digital Age
• Since computers use digital signals but phone
lines use analog, modems must translate from
digital to analog, send the signal along the
phone line, then translate back from analog to
digital at the other end
– The process is called “modulation/demodulation”
– Modulation means to translate from digital to analog
– Demodulation means to translate from analog to
digital
– Modems have to do all this just to use standard
analog voice phone lines
6-6
From the Analog to the
Digital Age
• Tape recorders, voices, and musical instruments are
analog while CDs are digital
• To burn a CD from a jam session, the digital recording
equipment must convert from analog to digital
– The analog-to-digital converter samples the sound and converts
the height of the wave to a number
– Samples of the sound wave are taken at regular intervals –
about 44,100 times each second
– Because the digital samples are played back
faster than our ears can react, it sounds to us
like a single continuous sound wave
6-7
From the Analog to the
Digital Age
• Digital sampling is similar to showing movies
– Movies show still pictures (frames)
– But they show them so fast that our eyes can’t react
in time
– So to us the series of still pictures look like continuous
motion
– Did you ever notice in movies when they show car
tires in motion they sometimes seem to move
backwards?
• This is because the tires are moving at a rate that is
incompatible with the frame rate of the movie, so our eyes
think the tires are really moving backwards when the car is
actually moving forward!
6-8
Networks
• A system of interconnected computers,
telephones, or other communications devices
that can communicate with one another and
share applications and data
• 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
6-9
Networks
• Since the days of “sneakernet”, networks
have become standard. They enable us to:
– 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
6-10
Networks
• WAN – Wide Area Network
• Covers a wide geographic area,
such as a country or the world
• Covers a city or a suburb
• MAN – Metropolitan Area
Network
• LAN – Local Area Network
• Connects computers and devices
in a limited geographic area such
as an office, building, or group of
nearby buildings
• Uses wired, cable, or wireless
connections to link a household’s
digital devices
• Uses short-range wireless
technology to connect an
individual’s personal electronics
like cellphone, PDA, MP3 player,
notebook PC, and printer
• HAN – Home Area Network
• PAN – Personal Area Network
6-11
Networks
• 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
– Mail servers manage email
• Peer-to-Peer
– All computers on the network communicate directly
with each other without relying on a server
– For fewer than 25 PCs
6-12
Networks
• Peer-to-Peer (continued)
– 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
• 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 since
there is no central server to shut down
– So publishers are suing individual downloaders instead
Watch out!
6-13
Don’t download illegally!
Networks
Intranets, Extranets, VPNs
• Intranets
– An organization’s private network that uses the
infrastructure and standards of the internet and the
web
• Extranets
– Private internets that connect not only internal
personnel but also selected suppliers and other
strategic parties
• Virtual Private Networks
– Private networks that use a public network, usually
the internet, to connect remote sites
6-14
Network
Components
• Connections
– Wired – twisted-pair, coaxial cable, or fiber-optic
– Wireless – infrared, microwave (Bluetooth), broadcast
(Wi-Fi) or satellite
• 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
6-15
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
6-16
Network
Packets
• TCP/IP Packets carry four types of information
– Sender’s address (source IP number)
– Address of intended recipient (destination IP number)
– 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
– 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 they can be
read
6-17
Network
• Daisy
Chain
• Hub
• Switch
• Bridge
• Gateway
• Router
• Backbone
Devices
• Used in peer-to-peer networks – direct
connections from one PC to the next
• Used in small LANs to connect PCs and LAN
segments to each other. Forwards to all ports
• Used in larger, busy LANs – faster than hubs
because it forwards only to correct
destination
• Used to connect two networks of the same
type
• Connects two networks of different types
• Connects multiple LANs together. Routers
are the internet backbone
• The main route that connects all the
gateways, routers, and other computers in an
organization
6-18
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
6-19
Network
Packet Collision Schemes
• Collisions happen when two data packets are
going opposite directions on shared media
• 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
Pricier than
– Token is sent around the ring
Ethernet
– Wait to get the token, then send data
6-20
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
• Carries voice and data up to 200 megabits per second
6-21
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
6-22
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
6-23
Kesimpulan
24