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CSCI-235
Micro-Computer Applications
The Network
Network Fundamentals

A computer network consists of
two or more computers linked
together to exchange data and
share resources

Communication is the process
of sending and receiving
messages

Communication channels are
the paths through which
messages are passed

Communication devices
transform electronic signals
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Putting Together a Network

Basic Components



Sending device
Communications link
Receiving device
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A Communications Model

Source


Transmitter


Carries data
Receiver


Converts data into transmittable signals
Transmission System


generates data to be transmitted
Converts received signal into data
Destination

Takes incoming data
Simplified Communications
Model - Diagram
Simplified Data
Communications Model
Continuous & Discrete Signals
Frequency Domain Concepts
 Signal
usually made up of many
frequencies
 Components are sine waves
 Can be shown (Fourier analysis) that any
signal is made up of component sine
waves
 Can plot frequency domain functions
Addition of Frequency
Components
Data Rate and Bandwidth
 Any
transmission system has a limited
band of frequencies
 This limits the data rate that can be carried
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Bandwidth
 Bandwidth
is usually used to refer to the
data rate (i.e., the amount of data that can
be transmitted through a communications
channel)
 Digital bandwidth is measured in bits per
second (bps), kilobits per second (Kbps),
megabits per second (Mbps), or gigabits
per second (Gbps)
 Low bandwidth is 56 Kbps and high
bandwidth is 622 Mbps
Modems: From Digital to Analog
and Back
Modulation
Analog
Digital
Demodulation
Analog

Digital
Modems are devices that transform signals when
sending and receiving transmissions

Modulation – Transforming digital signals to analog

Demodulation – Transforming analog signals to digital
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Networking
 Point
to point communication not usually
practical


Devices are too far apart
Large set of devices would need impractical
number of connections
 Solution
is a communications network
Switching and Routing Techniques
Circuit switching
 Networks create an endto-end circuit between the
sending and receiving
computers
 Electronic switches
establish and maintain
the connection
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


Packet switching
Outgoing messages are
divided into fixed-size
data units called packets
Packets are numbered
and addressed to the
receiving computer
Routers examine the
packets and send them to
their destination
Advantages and Disadvantages
of Circuit and Packet Switching
Advantages
Disadvantages
Costly
Voice and real-time A direct electrical
Circuit switching transmission
connection between
No delivery delays the computers is
required
Efficient, less
Delays in receiving
expensive, and
packets
reliable
Packet switching
Not ideal for realWill function if part
time voice
of the network is
communication
down
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Protocols
 Protocols
are fixed, formalized standards
that specify how computers can
communicate over a network
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Network Layers
user
layer
physical media


receiving
sending
protocol
user
stack
physical media
Network architecture is the overall design of a network
The network design is divided into layers, each of which
has a function separate from that of the other layers
 Protocol stack – The vertical (top to bottom) arrangement
of the layers; each layer is governed by its own set of
protocols
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Advantages of Networking
Reduced hardware costs
 Users share equipment
Connected people


Shared applications
Users share software
File server enables all
users to work with the
same application program
 People can work
together without being
at the same location
 Groupware enables
sharing of schedules
and communications
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Building information
resources
 Users create common
pools of data that can be
accessed by employees
Types of Computer Networks
Local Area Network
(LAN)
 Links computers within a
Wide Area Network
(WAN)

Links computers separated
by a few miles or
thousands of miles

Uses long-distance
transmission media
building or group of
buildings
 Uses direct cables, radio,
or infrared signals
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Local Area Networks (LANs)
 Network
access is controlled by a network
administrator
 Users
can access software, data, and
peripherals

LANs require special hardware and software
 Computers
connected to a LAN are called
workstations or nodes
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LAN Hardware and Software
Networking Hardware
Networking Software
 Network interface card
 Operating system that
(NIC) – Provides the
connection between the
computer and the network
 Inserted into a computer’s
expansion slot
supports networking
(Unix, Linux, Windows,
Mac OS)
 Additional system
software
NIC
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Peer-to-Peer Networks
 All computers on the network are treated as
equal
 Users decide which files and peripherals to
share
 Peer-to peer is not suited for networks with
many computers
 Peer-to-peer is easy to set up. Example: home
networks
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Client-Server Networks
 Typical corporate networks are client-server
 Clients send requests to servers for programs
and data, and to access peripherals
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Wide Area Networks (WANs)

WANs are similar to long-distance
telephone systems
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WAN Applications
LAN-to-LAN
 WANs are used to connect LANs at two or
more geographic locations
 Companies
use WANs to connect their
branches to one network system
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Backbones
 Backbones,
high-capacity transmission
lines, are regional, continental, or
transcontinental
 Internet backbones can carry 2.5 gigabits
of data per second
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