IntroductiontoInform.. - Home (www.dginter.net)
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Transcript IntroductiontoInform.. - Home (www.dginter.net)
Introduction to Information
Networking
How to get the bits from here to there.
Or
If I was going there I wouldn’t start
from here.
What is a Network?
Devices and media used to transfer
information from place to place in
real-time.
Examples:
• Phone System
• Cable TV System
• Internet
Today these all converge.
Basic Network Components
Hosts: Communicators. Devices that send
and receive data.
Devices: used to interconnect hosts.
• Hubs, switches routers……
Media: used to interconnect devices.
• Ethernet, Fiber, Token Ring, Coaxial, Space
(WiFi)
Shared Peripherals: Assets connected to
a host (printer, cd-tower, web camera)
Network Roles
Client: user of data
Server: provider of data or service
Client/Server: provider and
consumer of data.
• In the real world, all servers are also
clients. As an example, web servers use
Domain Name Servers to look up
Internet Addresses.
Source Channel and Destination
Source: needs to send a message.
Destination: where the message
should go.
Channel: how to get there from here.
Example 1
Fred needs to Wilma to pick up bread on
the way home.
Fred sends e-mail to Wilma.
Source=Fred; Destination=Wilma
Channel:
• Ethernet TCP/IP from Computer to Home
Router
• Home Router to ISP via cable/dsl/..
• Home ISP to Wilma’s employer’s ISP via Cloud
(magic).
• Employer’s Router to Wilma’s Computer via
Ethernet
Example 2
Betty needs to Barney to pick up bread on
the way home.
Betty sends ext message to Barney.
Source=Betty; Destination=Barney
Channel:
• SMS Cellular Connection from Betty’s Cell to
nearest available Cell Tower
• Betty’s Cell Tower to Cell Tower near Barney
via Public Switched Telephone Network (PSTN)
aka Plain Old Telephone System (POTS).
• Barney Cell Tower to Barney’s cell using SMS.
Protocols
Rules for Communication.
Human Example: Phone Call
• Caller Dials Number
• PSTN finds receiver and creates
connection.
• Receiver Phone Rings. Receiver Picks Up
• Caller Identifies themselves.
• Both talk using the same language.
Hopefully they both listen for silence before
speaking.
Protocols are Everywhere
Encoding: preparing the message for
transfer.
Format: Agreeing on what is where.
Size: Setting a limit on how much
can be sent at once.
Timing: when (access), how much
(flow control), timeouts (max wait).
Protocol Matching
All Protocols must match for
communication to occur.
• Ethernet is a protocol to physically
transfer data. Physical protocols must
match for all connecting devices.
• TCP/IP is a set of protocols to send data
over a physical network. Communication
Protocols must match at ends.
Network Stacks
Communication across networks is
difficult and needs to be chunked
into smaller manageable pieces.
OSI has a seven layer protocol that
defines the “ideal” network.
TCP/IP is the real-world winner of
the network protocols has a four
layer protocol.
OSI Model
Layer Name
What it does.
Application
Defines the rules.
Presentation
Data type, Encryption
Session
Open, close communication
Transport
End-to-end reliability,
slices/dices/reassembles
Network
Routing. How to get there ….
Data Link
Node-to-node, error ID.
Physical
Spits Bits. Rules for spitting bits
Mnemoic: All People Seem To Need Data Processing. There are worse!
TCP/IP Stack
Layer Name What it Does
Application
Transport
Internet
Network
Interface
Defines service rules,
encryption, encapsulation
End-to-end reliability,
chunking, sequencing
Routing
Frames data for transmission
and transmits. Is equal to the
Network Interface Card.
Data Transmission
Copper Wire
• Phone System
• Ethernet
Fiber Optic
• Long Haul
• Cable Distribution
Airwaves
• Radio/TV
• WiFi
• Bluetooth
Data Transmission Terms
Attenuation: Loss of signal over
distance
Noise: random unwanted signals.
• Electric motors, fluorescent lights,
crosstalk
Signal Spread: high frequency
attenuates more than low.
Copper Wire
Coaxial Cable.
• Advantages
• Highly immune to RFI
• High SNR
• Disadvantages
• Cost, size, Installation,
Access
Twisted Pair
• More twists less noise
• Can be shielded but is
expensive (manufacturing
and installing)
Optical Fiber
Transmits Photons.
Core is low
attenuation.
Cladding is high
attenuation.
Boundary is reflective.
Single (60-100km)
and MultiMode (2km)
That’s about 36-62
miles versus 1.2 miles
Disadvantage: $$$$$
Wireless
Unguided Transmission.
Higher Frequencies do not bend
Wireless can reflect off different
surfaces. i.e. Microwave reflects off
stone and steel but passes through
wood or sheet rock.
Prone to interference (other devices)
Common Bands: 0.9, 2.5, 5.0, & 5.8 GHZ
Using Waves to Transmit Data
f(t) = Asin(2πft + θ)
The Sine Wave
Amplitude Modulation
Frequency Modulation
Transmitting Digital Data using
Analog Signalling
PSK, a finite number of phases are
used.
FSK, a finite number of frequencies
are used.
ASK, a finite number of amplitudes
are used.
QAM, a finite number of at least two
phases, and at least two amplitudes
are used.