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1.12 Networking Concept
Data Communications: No Need to Be There
- Originally,
computer hardware was all kept in one place
- Decentralisation
- telephone lines
- Distributed
data processing (DDP)
- Value of
computer communications
Electronic Mail
- Sending
messages directly - one computer to another
Teleconferencing
- Part of CSCW
technology (computer support co-operative work)
- To bring
people 'together' despite geographic barriers.
- Videoconferencing
The Internet
- It is the
largest and most far-reaching network system of all time
- A loosely
organised collection of about 25,000 networks worldwide.
- No one owns
the Internet.
- Needs a
server with Internet protocol
- Individuals
are billed at an hourly or monthly rate
- Research and education activities (original purpose) Vs
business related (more than half)
- Benefits for
business
- The future
for business
Components of a typical Network:
Basic components of a data communications system:
- A sending
device
- A
communications link
- A receiving
device.
Design Considerations
- Data
transmission speed
- Types of
communication links
- Network topology:
- Local area
network
- Wide area
network
- Location of
peripherals such as disks and printers
- Data Transmission Speed
- Computer
communication = digital
transmission
= distinct pulses (in the form of on or off)
- Media
communications (voice transmission) = analog
transmission
= continuous electric signal (in the form of a wave)
- Carrier wave
to convert digital signals to analog form
- Two flexible
characteristics of a carrier wave:
- Amplitude: the height
of the wave
- Frequency: the number
of wave repetitions over a specific interval
- Modulation: process of
conversion from digital to analog signals
- Demodulation: reverse
- Modems: Converts a
‘DIGITAL’ signal to ‘ANALOG’ signal
- Modem data
speeds:
- Old speed:
1200, 2400, and 9600 bps (bits per second)
- Modem: 14,400
bps and 28,800 bps.
BIT = A Binary Digit
Types of Communications Links
The physical medium used for data transmission (wires and cables)
i.
TWISTED
PAIR
- Sensitive to
electrical pulses (copper)
ii. FIBBER OPTICS
- High-quality
transmission - a single conductor wire
- Made of
glass fibres
- Thinner than
a human hair
- Send data
via light beams (all types of data voice, pictures, music, video at same time)
- Materials
are lighter and less expensive than wire cables
- The
University of Nottingham:
- 1,200 (bits
per second - bps) 1985
- 2,400
(twisted pair)
- 9,600
- 28,000
- 1,000,000
(fibber optics)
- 10,000,000
- 100,000,000
1998
iii. MICROWAVE TRANSMISSION
- Line-of-sight
transmission of data signals through the atmosphere, using relay stations
(30 miles apart)
- Speed, cost
effectiveness, and ease of implementation.
iv. SATELLITE TRANSMISSION
- Uses earth
stations to send and receive signals from satellites
- A satellite
is hanging in space about 22,300 miles away.
3.
Network Topologies:
It is the physical layout of a network.
A. Local Area Networks (LAN)
- A local area
network (LAN) is a collection of computers, usually personal computers
that share hardware, software, and data.
- Cover short
distances (one office or building)
- Terminology:
- Server - PC with
large hard disk (holds shared files) – controls network
- A node – A
computer on a network
- A
network-interface card
(NIC) – includes electronic components to
send and receive massages
Three basic topologies:
- Star network
- A hub
computer
- All
messages are routed through the central computer
- Ring network
- Circular
manner
- Data travel
in one direction
- Data is
examined by the node to see if it is the addressee
- If not, the
data is passed on
- If one node fails then the entire network fails.
- Bus network
- Has a
single line
- Nodes can
be attached to or detached without affecting the network
- If one node
fails it does not affect the rest of the network
Two ways to organize the resources of a LAN:
- Client/server: processing
is done by the server, the results sent to the node
- File server:
processing is done by the node, the entire file is sent by server
B. Wide Area Networks (WAN)
- A network of
geographically distant computers and terminals.
- Contain
computer systems (Mainframe, minicomputer).
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