Management information system ralp 7e ch06

• 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 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 receiver gets the
message instantaneously
• Asynchronous communications: 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: can transmit data in only one direction
• Half-duplex channel: can transmit data in either direction,
but not simultaneously
• Full-duplex channel: 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:
states that the information-carrying capacity of a channel
is directly proportional to its bandwidth
• Broadband: telecommunications in which a wide band
of frequencies is available to transmit information

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Types of Media
• 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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