Chapter 6
Telecommunications &
Networks
Communication Model
 Message is communicated via a signal
 Transmission medium (communication channel)
“carries” the signal
Encode
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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
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 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
Hierarchical
Star
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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
 File Server
 Applications & databases
reside on host mainframe
computer
 User accesses applications
via a “dumb” terminal
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
 Disadvantages
 Reduced costs
 Improved performance
 Increased security
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 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 longdistance 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 &
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 Case: Nav Canada, pages 284-285
 Next Class: Chapter 7
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