Information Technology for
Computer network and typologies
Internet (TCP/IP & HTTP) and how it works
Voice over IP (VoIP)
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Similar to the way we sometimes think about human communication
electronic signal (data, message)
sender channel receiver
Sender & Receiver – special devices (cell phone, email client computer, etc.). Similar
to people talking to each other, one talks, the other listens.
Technical standards (protocol) that define sender and receiver and how they
communicate (establish connection, ensure transmission, etc.). People also use rules:
self-introduction, language or vocabulary selection, watching reactions to speech…
Data – the content transmitted. People: the content of speech.
Channel - The form of energy by which data travel (electrical signal in wire, electro-
magnetic wave, light…). People: voice via air waves. *see Note
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The amount of data transmitted through a channel in unit of time.
Used as a measure of a capacity of telecommunications channel.*
Fiber optic cable Trillions of bits/sec
Coaxial cable used for Internet access at Billions of bits/sec
Radio Frequency Wave used for cell Thousands of bits/sec
Notice that the measure of data transmission speed is bits per
second. In contrast, the measure for computer storage uses the
term bytes (and larger measures, like megabyte).
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Computer Network is a set of nodes (computers, printers, and other
equipment) linked via a communication channel.
Two kinds: Local and Wide Area networks
Local Area Network (LAN)
Covers a smaller area (one or more buildings like the campus)
Example: Ethernet – the bus network software by Xerox corp.
(different than “Internet”); see next slides
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• Wide Area Network (WAN)
• Covers a larger area (a region, across continents)
• Proprietary software l(e.g., IBM’s global corporate network)
• Internet (not proprietary, but a set of rules for connecting
different proprietary networks across – see next slides)
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LAN Typologies: Star Network
All computers are connected to a
All communications between computers
must pass through the central node
– centralized network.
Better communications control, but if
central node goes down – the whole
network is down (high-risk).
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All computers are linked on the same
All messages are broadcast to the entire
network – decentralized network.
Simple to set up and manage, but
collision between messages possible
(if that happens, all senders must
send again). Collision detection
feature reduces the problem.
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All computers are linked by a circular
container Message is passed in one direction from
one node to another
Better control and no collision, but
management more complex than
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TCP/IP is a set of rules (or a network protocol or standard) that define
communications rules. These rules are implemented in network software of
different vendors and operating systems. Two LANs that “support TCP/IP” are
said “to be on the Internet”.
Internet standard defines 4 “layers” that work together both on the sender and
receiver side: Sender Receiver
file transfer (FTP,
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How Internet Works
SMTP to TCP:
“Take this message SMTP restores original format
and send it to this of message and presents it.
TCP Breaks message into
packets and passes these Put reassembles packets
to IP. in proper orders and checks
sum of data received vs.
IP scans Internet
addresses and Accepts packets and
routers on the way to reports back to routers.
receiver. IP puts address
on each packet and
passes them to Network.
Gets packets off com-
Network physically puts munication medium.
packets onto the com-
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Voice over IP (VoIP)
Using Internet as telephone network (voice and text & video;
Based on new Internet protocol – VoIP
Computers act as VoIP phones or special VoIP phones used
VoIP phone has an Internet address and can act as Internet
node anywhere without changing its “number” (IP address)
Big savings in comparison to classical phone
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This is the future! *
Use RF waves (see Note to slide on Telecommunications model)
(1) WiFi Standard
Used in wireless LANs (PCs, laptops support WiFi)
Cell phones have WiFi capability and thus can be a LAN node
When LAN is linked to the Internet, a WiFi laptop or cell phone
connects to the Internet (e.g., LAN in Drake Ctr. with “hot
spots”); see Note **
WiMAX version of this standard covers 50 km range
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(2) Personal Area Network Standards
Covers 10m in diameter, 10 devices connected
Used for connecting:
microphone and headphones to cell phone
keyboard & mouse to CPU
computer to printer
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