• 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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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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