Chapter 6: Telecommunications & Networks

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7 Νοε 2013 (πριν από 3 χρόνια και 9 μήνες)

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Telecommunications &
Networks

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Communication Model


Message is communicated via a signal


Transmission medium (communication channel)
“carries” the signal

Encode

Decode

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Telecommunications


Electronic

transmission of signals, e.g., telephone,
radio, television


Telecommunication medium:
Anything that
carries an electronic signal & interfaces between a
sending device & a receiving device


Data Communications:
A subset of
telecommunications referring to the sending,
transmission, & receiving of data
--

typically
between computer systems

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Communications & Telecommunications

In human speech, signals are transmitted through the
air; in telecommunications, signals are transmitted
through various media

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Elements of Telecommunications

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Types of telecommunication Media (1)


Twisted Pair


Insulated copper wire


Electrical signals


Coaxial Cable


Inner wire core surrounded by shielding


Electrical signals


Higher transmission speeds than twisted
pair


Fiber
-
optic Cable


Extremely thin strands of glass bound
together


Light pulse signals


Very high transmission speeds

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Types of Telecommunication Media (2)


Microwave


Satellite

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Types of Telecommunication Media (3)

Cellular

transmission signals are transmitted to
receivers & integrated into the regular network.


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Modems

Translate
digital

signals
to analog

for transmission
over the
Public Switched Telephone Network
(PSTN)

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Carriers & Services (1)


Common Carriers:

Long distance telephone
companies (AT&T, Sprint)


Value
-
Added Carriers:
Private telecom systems
offering enhanced services for a fee


Switched Lines:
Circuits that use switching
equipment to allow one device to connect to other
devices (typical phone lines)


Dedicated Lines:
Point
-
to
-
point circuits with no
switching or dialing



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Carriers & Services (2)


Private Branch Exchange (PBX)


Telecommunications switching equipment that allows
users within an organization to share outside lines


Capable of handling both voice & data traffic


Integrated Services Digital Network (ISDN)


Uses existing telecommunications infrastructure to
simultaneously transmit digital voice, data, & video


Being phased out in North America (cable & ADSL are
replacing this service)


T1 Circuits


High speed dedicated lines (1.54 Mbps)


Equivalent to 24 regular voice lines

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Types of Network Configurations

Ring

Bus

Star

Hierarchical

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LANs & WANs


Local Area Network (LAN):
Connects computer
systems & devices in the same geographic area
(can be ring, bus, hierarchical, star, hybrid)


Wide Area Network (WAN):
Ties together large
geographic regions using microwave & satellite
transmission or telephone lines


International Network (Global Area Network:
GAN):

Links systems between countries

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Types of Computing Connectivity (1)


Terminal
-
to
-
Host


Applications & databases
reside on host mainframe
computer


User accesses applications
via a “dumb” terminal



File Server

File server transfers data &
programs to PCs on the
network where the PCs
perform most processing.

“Dumb”

terminal

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Types of Computing Connectivity (2)


Client/Server


Applications & databases reside on specialized host
computers (servers)


Processing is shared between the host server & the
client


Client & server may be different types of computers

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Advantages & Disadvantages of
Client/Server Computing


Advantages


Reduced costs


Improved performance


Increased security


Disadvantages


Increased costs


Loss of control


Complex multi
-
vendor
environment

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Communication Software


Communications Software:
Provides error
checking, message formatting, communication
logs, data security/privacy, & translation
capabilities for networks


Network Operating System (NOS):
Systems
software that controls the devices on a network &
allows them to communicate with each other


Network Management Software:
Monitors the
use of network resources, scans for viruses, &
ensures compliance with software licenses

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Communication Protocols


Protocol:
Rules that ensure communications
among different types of computers from multiple
manufacturers


Open Systems Interconnection (OSI):
Leading
protocol “model”; comprised of 7 layers


Transmission Control Protocol/Internet Protocol
(TCP/IP):
Two communication protocols of the
Internet that work together (rapidly overtaking OSI)


Systems Network Architecture (SNA):
IBM’s
proprietary communication protocol


Ethernet:
Protocol standard developed for LANs
using a bus topology


X.400 & X.500:
Standards for message handling
& network directories

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Bridges, Routers, Gateways, &
Switches


Bridge:
Connects two or more networks
that use the same protocol at the media
control sublayer of the data link layer


Router:
Operates at the network level of
the OSI model with more sophisticated
addressing software than bridges; can
determine preferred paths


Gateway :
Operates at or above the OSI
transport layer & links LANs or networks
that employ different architectures & use
dissimilar protocols


Switch:
Switches data to its destination
by a point
-
to
-
point (rather than shared)
connection

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Telecommunications Applications (1)


Linking computers & data terminals:
Download

&
upload

information


Voice Mail
: Enables users to send, receive, &
save verbal messages, including sending the same
message to a “group”


E
-
mail
: Enables users to send, receive, & save
text messages & attached documents


Telecommuting
: Enables employees to work
away from the office using PCs & networks to
communicate electronically

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Telecommunications Applications (2)


Videoconferencing

Allows participants to
conduct long
-
distance meetings
“face to face” while
eliminating travel


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Telecommunications Applications (3)


Electronic Data
Interchange (EDI)


Uses networks to allow
output from one
organization’s system
to be processed
directly as input to
another organization’s
systems, without
human

intervention;
follows standards &
procedures

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Case: Nav Canada, pages 284
-
285



Next Class: Chapter 7