COMPUTER APPLICATIONS Waxahachie High School

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COMPUTER APPLICATIONSWaxahachie High School

• Communications
• And
• Networking
• TA TEKS (1)(A), (1)(D), (1)(G), (1)(I)

Source Computers Tools for an Information Age
(Capron and Johnson)
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COMMUNICATIONSAND NETWORKING

• LESSON OBJECTIVE
• Describe the basic components of a network.
• Explain the methods of data transmission,
  including types of signals, modulation, and
  choices among transmission modes.
• Differentiate among various kinds of
  communications links and explain the need for
  protocols.
• Describe various network configurations.
• List the components, types, and protocols of a
  local area network.

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COMMUNICATIONSAND NETWORKING
Data communications systems are computer systems
that transmit data over communications lines,
such as telephone lines or cables. Centralized
data processing places all processing, hardware,
and software in one central location. Businesses
with many locations or offices often use
distributed data processing, which allows both
remote access and remote processing.
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COMMUNICATIONSAND NETWORKING
Communications system components. Data
originating from (1) a sending device is (2)
converted by a modem to data that can be carried
over (3) a communications link and (4)
reconverted by a modem at the receiving end
before (5) being received by the destination
computer.
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COMMUNICATIONSAND NETWORKING
A network is a computer system that uses
communications equipment to connect two or more
computers and their resources. The basic
components of a data communications system are a
sending device, a communications link, and a
receiving device. Digital transmission sends data
as distinct on or off pulses. Analog
transmission uses a continuous electric signal in
a carrier wave with a particular amplitude and
frequency.
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COMMUNICATIONSAND NETWORKING
Digital signals are converted to analog signals
by modulation (change) of a characteristic, such
as the amplitude (height) or frequency of the
carrier wave. Demodulation is the reverse
process both processes are performed by a device
called a modem.
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COMMUNICATIONSAND NETWORKING
Analog signals. (a) an analog carrier wave moves
up and down in a continuous cycle. (b) The analog
waveform can be converted to digital form through
amplitude modulation. The wave height is
increased to represent a 1 or left the same to
represent a 0. (c) In frequency modulation, the
amplitude of the wave stays the same, but the
frequency increases to represent a 1 or stays the
same to indicate a 0.
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COMMUNICATIONSAND NETWORKING
Modems convert (modulate) digital data signals in
analog signals for sending of communications
links, then reverse the process (demodulate) at
the other end.
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COMMUNICATIONSAND NETWORKING
An external modem is not built into the computer
and can therefore be used with a variety of
computers. An internal modem is on a board that
fits inside a personal computer. Notebook and
laptop computers often use a PC card modem that
slides into a slot in the computer. Modem speeds
are usually measured in bits per second (bps).
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COMMUNICATIONSAND NETWORKING
PC Card Modem
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COMMUNICATIONSAND NETWORKING
An ISDN adapter, based on Integrated Services
Digital Network (ISDN), can move data at 128,000
bps, a vast improvement over any modem. Digital
subscriber line (DSL) service uses advanced
electronics to send data over conventional copper
telephone wires many times faster than a
conventional modem.
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COMMUNICATIONSAND NETWORKING
Cable modems use the cable TV system to transmit
data at very high speeds. The actual speed
depends on the number of subscribers in a
neighborhood using the service. Cellular modems
can be used to transmit data over the cellular
telephone system.
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COMMUNICATIONSAND NETWORKING
Two common methods of coordinating the sending
and receiving units are asynchronous transmission
and synchronous transmission. The asynchronous
method keeps the units in step by including
special signals at the beginning and end of each
group of message bits (usually a character). In
synchronous transmission, the internal clocks of
the units are put in time with each other at the
beginning of the transmission, and the block of
characters is transmitted in a continuous stream.
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COMMUNICATIONSAND NETWORKING
Simplex transmission allows data to move in only
one direction (either sending or receiving).
Half-duplex transmission allows data to move in
either direction but only one way at a time. With
full-duplex transmission, data can be sent and
received at the same time.
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COMMUNICATIONSAND NETWORKING
A communications medium is the physical means of
data transmission. Bandwidth refers to the range
of frequencies that a medium can carry and is a
measure of the capacity of the link. Common
communications media include wire pairs (or
twisted pairs), coaxial cables, fiber optics,
microwave transmission, and satellite
transmission.
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COMMUNICATIONSAND NETWORKING
In satellite transmission, which uses earth
stations to send and receive signals, a
transponder in the satellite ensures that the
stronger outgoing signals (the downlink) do not
interfere with the weaker incoming (uplink) ones.
Noise is anything that causes distortion in the
received signal.
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COMMUNICATIONSAND NETWORKING
(a) To relay microwave signals, dish-shaped
antennas are often located atop buildings and
towers because they can only follow a
line-of-sight path. (b) A satellite acts as a
relay station to avoid interference from the
curvature of the earth.
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COMMUNICATIONSAND NETWORKING
Satellite Dish
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COMMUNICATIONSAND NETWORKING
The following wireless transmission techniques
are used to transmit data over short distances
IrDA uses infrared to transmit data a few feet,
Bluetooth uses radio waves to connect mobile
devices over distances less than 30 feet. The
802.11 family of standards is used for
transmission up to about 150 feet and includes
802.11b (also known as Wi-Fi), 802.11a, and
802.11g.
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COMMUNICATIONSAND NETWORKING
A protocol is a set of rules for exchanging data
between a terminal and a computer or between two
computers. The protocol that makes Internet
universality possible is Transmission Control
Protocol/Internet Protocol (TCP/IP), which
permits any computer at all to communicate with
the Internet.
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COMMUNICATIONSAND NETWORKING
The physical layout of a local area network is
called a topology. A node usually refers to a
computer on a network or used to refer to any
device that is connected to a network, including
the server, computers, and peripheral devices
such as printers. A star network has a central
computer, the hub, that is responsible for
managing the network. A ring network links all
nodes together in a circular manner. A bus
network has a single line, to which all the
network nodes are attached.
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COMMUNICATIONSAND NETWORKING
(a) Star Network (b) Ring Network (c) Bus
Network
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COMMUNICATIONSAND NETWORKING
A wide area network (WAN) is a network of
geographically distant computers and terminals. A
metropolitan area network (MAN) uses similar
technologies, but is limited to a single
metropolitan area. WANs typically use
communication services provided by common
carriers. These services are switched, or
dial-up, and dedicated. The public telephone
system, sometimes referred to as plain old
telephone service (POTS), is the most common
dial-up system. Common carriers provide dedicated
service over leased lines.
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COMMUNICATIONSAND NETWORKING
WANs are normally controlled by one or more
mainframe computers, called host computers. These
host computers typically connect to the WAN
through a front-end processor (FEP) that handles
communications tasks. A multiplexer combines the
data streams from a number of slow-speed devices
into a single data stream for transmission over a
high-speed circuit.
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COMMUNICATIONSAND NETWORKING
To communicate with a mainframe, a personal
computer must employ terminal emulation software.
When smaller computers are connected to larger
computers, the result is sometimes referred to as
a micro-to-mainframe link. In a situation in
which a personal computer or workstation is being
used as a network terminal, file transfer
software enables a user to download files
(retrieve them from another computer and store
them) and upload files (send files to another
computer).
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COMMUNICATIONSAND NETWORKING
A local area network (LAN) is usually a network
of personal computers that share hardware,
software, and data. The nodes on some LANs are
connected by a shared network cable or by
wireless transmission. A network interface card
(NIC) may be inserted into a slot inside the
computer to handle sending, receiving, and error
checking of transmitted data.
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COMMUNICATIONSAND NETWORKING
If two LANs are similar, they may send messages
among their nodes by using a bridge. A router is
a special computer that directs communications
traffic when several networks are connected
together. Since many networks have adopted the
Internet protocol (IP), some use IP switches,
which are less expensive and faster than routers.
A gateway is a collection of hardware and
software resources that connects two dissimilar
networks, including protocol conversion.
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COMMUNICATIONSAND NETWORKING
A wireless access point (also called a base
station) connects to a wired network and provides
wireless transmit/receive capabilities over a
radius of several hundred feet. All computers in
a peer-to-peer arrangement have equal status no
one computer is in control. With all files and
peripheral devices distributed across several
computers, users share each others data and
devices as needed.
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COMMUNICATIONSAND NETWORKING
A client/server arrangement involves a server, a
computer that controls the network and provides
services to the client workstations. The server
has hard disks holding shared files and often has
the highest-quality printer. Processing is
usually done by the server, and only the results
are sent to the node. A computer that has no disk
storage capability and is used basically for
input/output is called a thin client. A file
server transmits an entire file to the node,
which does all its own processing.
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COMMUNICATIONSAND NETWORKING
Client/Server and File/Server
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COMMUNICATIONSAND NETWORKING
Ethernet is a type of network protocol that
accesses the network by first listening to
determine whether the cable is free this method
is called carrier sense multiple access with
collision detection, or CSMA/CD. If two nodes
transmit data at the same time, a collision
occurs. A Token Ring network controls access to
the shared network cable by token passing.
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COMMUNICATIONSAND NETWORKING
Office automation is the use of technology to
help people do their jobs better and faster.
Electronic mail (e-mail) allows workers to
transmit messages to other peoples computers.
Facsimile technology (fax) can transmit text,
graphics, charts, and signatures. Fax modems for
personal computers can send or receive faxes, as
well as handle the usual modem functions.
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COMMUNICATIONSAND NETWORKING
Groupware is any kind of software that lets a
group of people share things or track things
together, often using data communications to
access the data. Teleconferencing is usually
videoconferencing, in which computers are
combined with cameras and large
screens. Electronic data interchange (EDI) allows
businesses to send common business forms
electronically.
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COMMUNICATIONSAND NETWORKING
Videoconferencing System
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COMMUNICATIONSAND NETWORKING
In electronic fund transfer (EFT), people pay for
goods and services by having funds transferred
from various checking and savings accounts
electronically, using computer technology. The
ATM (automated teller machine), is a type of EFT.
In telecommuting, a worker works at home and
uses a personal computer to communicate with
office colleagues and customers.
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COMMUNICATIONSAND NETWORKING
Telecommuting. An engineer works at home.
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COMMUNICATIONSAND NETWORKING
Example of a network for a toy manufacturer. (1)
Marketing bus LAN with (2) server and (3) modem
for outside reps. (4) Design bus LAN. (5) Bridge
connecting Marketing and Design. (6) Gateway to
access (7) mainframe computer which uses (8)
front-end processor to handle communications. (9)
Purchasing and Personnel directly connected to
mainframe. (10) T1 connection to the mainframe at
Headquarters.