Technology Guide 4

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21 Νοε 2013 (πριν από 3 χρόνια και 10 μήνες)

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1

Telecommunications

Technology Guide 4

2

Telecommunication System



Hardware


Communications media


Communications networks


Communications
processors




Communications software


Data communications
providers



Communication protocols



Communications
applications

A

telecommunication system

is a collection of compatible
hardware and software arranged to communicate information from
one location to another. The major components include;

3

Telecommunication System
(cont.)

4

Electronic Signals


Analog signals

are
continuous waves that
“carry” information by
altering the
amplitude

and
frequency

of the
waves.


Digital signals

are
discrete on
-
off pulses
that convey information in
terms of
1s

and

0s
, just
like the central
processing unit in
computers.



Telecommunications media can carry two basic types of signals;



5

Communication Processors


Modulation

refers to the conversion from digital to analog and
the reverse is
demodulation
.



The device that performs these two processes is called a
modem.



Modems are always used in pairs.



The unit at the sending end converts digital information into analog
signals for transmission over analog lines;


At the receiving end, another modem converts the analog signal
back into digital signals for the receiving computer.

6

Communication Processors
(cont.)


Two main alternatives to analog modems are:


Digital subscriber line (DSL)


Cable modem


A
multiplexor

is an electronic device that allows a single
communications channel (e.g, a telephone circuit) to carry data
transmissions simultaneously from many sources.



A
front
-
end processor

is
a
specialized computer
that
manages
all routing communications with peripheral devices.


7

Communications Media


Communications media
(channels)


refer to the
physical pathway or medium
for which data is
communicated from one
location to another.


There are two categories:


Wireline


Wireless


8

Wireline vs. Wireless Media

Wireline


Twisted pair wire


Coaxial cable


Fiber optic cable

Wireless


Cellular radio


Microwave transmission


Satellite transmission


Global positioning system


Radio & Infrared light


9

Wireless Technologies


Mobile computing

refers to
the use of portable computer
devices in multiple locations.




Personal communication
service (PCS
)

uses lower
-
power, higher frequency
radio waves than cellular
technology. As a result, PCS
cells are smaller, more
numerous and closer
together.


Personal digital assistants
(PDAs)

are small, pen
-
based,
hand
-
held computers capable of
digital communications
transmission.




Bluetooth

is a relatively new
technology that allows wireless
communication between mobile
phones, laptops, and other
portable devices.


10

Transmission Speed


Bandwidth

refers to the range of frequencies that can be sent
over a communications channel.


A

baud

is a detectable change in a signal (i.e., a change from a
positive to a negative voltage in a wire).


Baud rate

refers to the rate at which signals can be transmitted
through a communications channel.



Channel capacity

is usually divided into three bandwidths:


Narrowband
(e.g., telegraph lines)


Voiceband
(e.g., telephone)


Broadband

(e.g., microwave, cable, and fiber
-
optic media)


11

Transmission Direction


Simplex data transmission

uses one circuit in one direction
only

similar to a doorbell, a public announcement system, or
broadcast television and radio.



Half
-
duplex transmission

also uses only one circuit, but it is
used in both directions

one direction at a time.



Full
-
duplex transmission

uses two circuits for
communications

one for each direction simultaneously.


e.g, a common telephone

12

Transmission Mode & Accuracy


Data transmissions may be either asynchronous or synchronous;


Asynchronous

-

only one character is transmitted or received at a
time.


Synchronous

-

a group of characters is sent over a communications
link in a continuous bit stream while data transfer is controlled by a
timing signal initiated by the sending device.


Because the loss of even one bit could alter a character or
control code, data transmission requires
accuracy controls
.


These controls consist of bits called

parity bits.

13

Protocol


Protocol

refers to the
set of rules and procedures governing
transmission across a network
.


The simplest protocol is

polling
,

where a master device polls, or
contacts, each node.


In the
token passing approach
, a small data packet, called a
token
, is sent around the network.


In another approach called
contention
a device that wants to
send a message checks the communications medium to see if it
is in use.



The
Transmission Control Protocol/Internet Protocol
(TCP/IP)

is a protocol for sending information across sometimes
-
unreliable networks.

14

Communication Standards

The major types of standards are
;



N
etworking standards



T
ransmission standards



S
oftware standards


15

Networking Standards


One or more protocols define precisely how software programs on
different systems interact to accomplish the functions for each layer.




The Open Systems Interconnection (OSI)

model has seven layers,
each having its own well
-
defined function:


Layer 1:

Physical layer



Layer 5
: Session layer


Layer 2:

Data link layer


Layer 6:

Presentation layer


Layer 3:

Network layer



Layer 7:

Application layer


Layer 4:

Transport layer


16

Transmission Standards


A number of network bandwidth boosters address the need for
greater bandwidth on networks for advanced computing
applications.



These include
:


FDDI (fiber distributed data interface)


ATM (asynchronous transfer mode)


LAN switches


ISDN (integrated services digital network)


17

Interface & Topology


An
interface

is a physical
connection between two
communications devices.



Parallel data transfer



Serial data transfer



The
topology

of a network is
the physical layout and
connectivity of a network.



Ring topology



Bus topology



Star network

18

Network Size


Local area networks (LAN)


Gateway, bridge, router


Network Interface Cards


Private branch exchange
(PBX)


Wide area networks (WAN)


Value
-
added Network (VAN)


Packet Switching


Frame relay


Virtual private network
(VPN)


There are two general network sizes:



19

Centralized Architecture


Centralized computer systems

are centered around a large
computer, known as the
host
, that provides computational power
and internal storage.



Several devices that lack self
-
contained computer processors,
such as
“dumb”

terminals and printers, are connected to the
host.



Although mainframes have represented the dominant centralized
form of computing for over 30 years,
minicomputers,
workstations
, and
powerful PCs

are challenging that dominance.

20

Non
-
centralized Computing


Non
-
centralized computing

architectures are decentralized or
distributed.



Decentralized computing

breaks centralized computing into
functionally equivalent parts, with each part essentially a smaller,
centralized subsystem.




Distributed computing

breaks centralized computing into many
computers that may not be (and usually are not) functionally
equivalent.

21

Client/Server Architecture


The basic structure of
client/server architecture

is a client
device(s) and a server device(s) that are distinguishable, but
interact with each other.



In a client/server approach, the components of an application are
distributed over the enterprise rather than being centrally
controlled.




There are three application components that can be distributed:


the presentation component


the applications (or processing) logic


the data management component


22

Client/Server Architecture
(cont.)


There are five models of client/server implementation;




Distributed presentation




Remote presentation




Distributed function




Remote data management




Distributed data management

23

Peer
-
to
-
Peer Network Architecture


A
peer
-
to
-
peer network architecture

allows two or more
computers to pool their resources together.



There are several advantages of peer
-
to
-
peer architecture
:
:


There is no need for a network administrator.


The network is fast and inexpensive to set up and maintain.


Each computer can make backup copies of its files to other
computers for security.


It is the easiest network to build.


24

Open Systems


Open systems

provide flexibility in implementing IT solutions,
optimization of computing effectiveness, and the ability to provide
new levels of integrated functionality to meet user demands.




Connectivity

is the ability of the various computer resources to
communicate with each other through network devices without
human intervention.



Open systems

and
connectivity

have enabled networks to
completely span organizations.


25

Enterprise Networking


Portability

is the ability to move applications, data, and even
people from one system to another with minimal adjustments.



Interoperability

refers to the ability of systems to work together
by sharing applications, data, and computer resources.



Scalability

refers to the ability to run applications unchanged on
any open system where the hardware can range from a laptop
PC to a super computer.