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• Effective communications are essential to organizational
success
• Define the terms communications and telecommunications
and describe the components of a telecommunications
system
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• An unmistakable trend of communications technology is
that more people are able to send and receive all forms of
information over greater distances at a faster rate
• Identify broad categories of communications media and
discuss the basic characteristics of specific media types
• Describe how a modem works
• Explain the types of telecommunications carriers today and the
services they provide
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• Identify the benefits associated with a telecommunications
network
• Define the term network topology and identify five
alternatives
• Discuss the different communications protocols and
devices used for telecommunications
• Name three distributed processing alternatives and discuss
their basic features
• List some telecommunications applications that
organizations are benefiting from today
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An Overview Of Communications
Systems
• Communications: The communication is the
transmission of a signal by way of a medium from a
sender to a receiver
• Signal contains a message composed of data and
information
• In telecommunications, sender transmits a signal through
a transmission medium such as a cable
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Figure 6.2: Communications and
Telecommunications
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An Overview Of Communications
Systems (continued)
• Communications can be synchronous or asynchronous
• Synchronous communications: The communications in
which the receiver gets the message instantaneously
• Asynchronous communications: The communications in
which the receiver gets the message some period of time
after it is sent
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Telecommunications
• Telecommunications: electronic transmission of signals
for communications, via telephone, radio, television, etc.
• Data communications: subset of telecommunications that
refers to the electronic collection, processing, and
distribution of data, typically between computer system
hardware devices
• Telecommunications medium: anything that carries an
electronic signal and interfaces between a sending device
and a receiving device
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Figure 6.3: Elements of a
Telecommunications System
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Communications Channels: Basic
Communications Channel
Characteristics
• Communication channels can be classified as simplex,
half-duplex, or full-duplex
• Simplex channel: A communications channel that can
transmit data in only one direction
• Half-duplex channel: A communications channel that can
transmit data in either direction, but not simultaneously
• Full-duplex channel: A communications channel that
permits data transmission in both directions at the same
time
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Channel Bandwidth and InformationCarrying Capacity
• Bandwidth: The range of frequencies that an electronic signal
occupies on a given transmission medium
• Shannon’s fundamental law of information theory: The law of
telecommunication that states that the information-carrying capacity
of a channel is directly proportional to its bandwidth
• Broadband: In general, broadband refers to telecommunications in
which a wide band of frequencies is available to transmit
information, allowing more information to be transmitted in a given
amount of time.
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Types of Media
(types of telecommunication media)
There are various types of telecommunications media are
available. Each type exhibits its own characteristics,
including cost, capacity, and speed. Transmission media
can be divided into two broad categories:
• Guided transmission media: communications signals are
guided along a solid medium
• Wireless media: communications signals are sent over
airwaves
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Table 6.1: Transmission Media Types
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Table 6.1: Transmission Media Types
(continued)
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Modems
• A typical telephone line can only accommodate an analog
signal (a continuous, curving signal)
• A computer generates a digital signal representing bits
• Modem: a device that translates data from digital to
analog and analog to digital
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Figure 6.8: How a Modem Works
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Multiplexers
• Multiplexers: devices that allow several
telecommunications signals to be transmitted over a
single communications medium at the same time
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Figure 6.9: Use of a Multiplexer to
Consolidate Data Communications onto
a Single Communications Link
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Front-End Processors
• Front-end processors: special-purpose computers that
manage communications to and from a computer system
• Connect a midrange or mainframe computer to hundreds
or thousands of communications lines
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Figure 6.10: Front-End Processor
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Carriers and Services
• Local exchange carrier (LEC): a public telephone
company in the United States that provides service to
homes and businesses within its defined geographical area
• Competitive local exchange carrier (CLEC): a company
that is allowed to compete with the LECs, such as a
wireless, satellite, or cable service provider
• Long-distance carrier: a traditional long-distance phone
provider, such as AT&T, Sprint, or MCI
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Switched and Dedicated Lines
• Switched line: a communications line that uses switching
equipment to allow one transmission device to be
connected to other transmission devices
• Dedicated line: a communications line that provides a
constant connection between two points; also called a
leased line
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Voice and Data Convergence
• Voice over Internet protocol (VoIP): the basic transport
of voice in the form of a data packet using the Internet
protocol
• IP telephony is the technology for transmitting voice
communications over a network using an open standardsbased Internet protocol
• Voice and data convergence: the integration of voice
and data applications in a common environment
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WATS
• Wide-area telephone service (WATS): a fixed-rate longdistance telecommunications service for heavy users of
voice services
• IN-WATS service
• OUT-WATS service
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ISDN
• Integrated services digital network (ISDN): a set of
standards for integrating voice and data communications
onto a single line via digital transmission over copper
wire or other media
• ISDN requires special adapters at both ends of the
transmission line
• ISDN Basic Rate Interface
• ISDN Primary Rate Interface
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Figure 6.12: ISDN Network Switching
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T-Carrier System
• Introduced in the 1960s to support digitized voice
transmission
• Uses four wires and provides duplex capability
• T-1 carrier is capable of carrying 1.544 Mbps over copper
wire; commonly used in U.S., Japan, and Canada
• T-3 line is capable of transmitting data at a rate of
44.736 Mbps
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Digital Subscriber Line (DSL)
• Digital subscriber line (DSL): a telecommunications
technology that delivers high-bandwidth information to
homes and small businesses over ordinary copper
telephone wires
• Provides a transmission rate of 512 Kbps to 1.544 Mbps
from the central office to the subscriber
• Provides a transmission rate of about 128 Kbps from the
subscriber to the central office
• Can carry both data and voice signals
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Wireless Mobile
Table 6.3: Some Wireless Data Communications Options
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Networks
• Computer network: the communications media, devices,
and software needed to connect two or more computer
systems and/or devices
• Network nodes: the computers and devices on the
networks
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Network Types
• Personal area network (PAN)
• Local area network (LAN)
• Metropolitan area network (MAN)
• Wide area network (WAN)
• International network
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Network Topology
• Network topology: logical model that describes how
networks are structured or configured
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Figure 6.15: The Basic Network
Topologies
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Terminal-to-Host, File Server, and
Client/Server Systems
• Classifications based on how computers on the network
connect and interoperate
• Terminal-to-host: application and database reside on one
host computer, and the user interacts with application and
data using a “dumb” terminal
• File server: the application and database reside on one host
computer (file server)
• Client/server: multiple computer platforms are dedicated
to special functions such as database management, printing,
communications, and program execution
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Figure 6.18: Client/Server Connection
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Interconnecting Networks:
Communications Protocols
• Open Systems Interconnection (OSI) model
• Transmission Control Protocol/Internet Protocol (TCP/IP)
• Systems Network Architecture (SNA)
• IEEE 802.3 (Ethernet)
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Communications Protocols (continued)
• Frame Relay
• Asynchronous Transfer Mode (ATM)
• FireWire
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Wireless Communications Protocols
• Bluetooth
• IEEE 802.11b (Wi-Fi)
• IEEE 802.11g
• IEEE 802.16 (WiMax)
• IEEE 802.20 (MBWA)
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Wireless Communications Protocols
(continued)
• 1G
• 2G
• 2.5G
• 3G
• Multichannel Multipoint Distribution System (MMDS)
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Network Switching Devices
• Private branch exchange (PBX): an on-premise
switching system owned or leased by a private enterprise
that interconnects its telephones and provides access to
the public telephone system
• Bridge: a device used to connect two or more networks
that use the same communications protocol
• Switch: a telecommunications device that routes
incoming data from any one of many ports to a specific
output port that will take the data toward its intended
destination
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Network Switching Devices (continued)
• Router: a device or software in a computer that
determines the next network point to which a data packet
should be forwarded toward its destination
• Hub: a place of convergence where data arrives from one
or more directions and is forwarded out in one or more
other directions
• Gateway: a network point that acts as an entrance to
another network
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Network Basics: Basic Processing
Strategies
• Centralized processing: all processing occurs in a single
location or facility
• Decentralized processing: processing devices are placed
at various remote locations
• Distributed processing: computers are placed at remote
locations but connected to each other via a network
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Communications Software
• Network operating system (NOS): systems software
that controls the computer systems and devices on a
network and allows them to communicate with each other
• Network-management software: enables a manager on
a networked desktop to monitor the use of individual
computers and shared hardware, scan for viruses, and
ensure compliance with software licenses
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Telecommunications Applications
• Linking personal computers to mainframes and networks
• Voice mail
• Electronic software distribution
• Electronic document distribution
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Telecommunications Applications
(continued)
• Call centers
• Telecommuting
• Videoconferencing
• Electronic data interchange (EDI)
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Telecommunications Applications
(continued)
• Public network services
• Electronic funds transfer (EFT)
• Distance learning
• Specialized systems and services
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Summary
• Communications: the transmission of a signal by way of
a medium from a sender to a receiver
• In telecommunications, the sender transmits a signal
through a transmission medium such as a cable
• Transmission media types: twisted-pair wire cable,
coaxial cable, fiber-optic cable, microwave, cellular, and
infrared
• Telecommunications carriers can be divided into local
exchange carriers, competitive local exchange carriers,
and long-distance carriers
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Summary (continued)
• A computer network consists of the communications
media, devices, and software needed to connect two or
more computer systems and/or devices
• Network types: personal area network (PAN), local area
network (LAN), metropolitan area network (MAN), wide
area network (WAN), and international network
• Network topologies: ring, bus, hierarchical, star, and
hybrid
• Options for how computers on a network connect:
terminal-to-host, file server, and client/server
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Summary (continued)
• Communications protocols include the Open Systems
Interconnection (OSI) model, Transmission Control
Protocol/Internet Protocol (TCP/IP), IEEE 802.3
(Ethernet), etc.
• Network switching devices: private branch exchange
(PBX), bridge, switch, router, hub, and gateway
• Examples of telecommunications applications are voice
mail, electronic software distribution, telecommuting,
videoconferencing, electronic funds transfer, and distance
learning
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