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Chapter Preview
 In this chapter, we will study:
The basic components of a telecomm system
The technologies used in telecomm systems
Various ways to configure networks
Various ways that businesses use networks
today
Telecommunications
The transmission of different
forms of data (such as text,
audio, video, images, graphics)
from one set of electronic devices
over media to another set of
geographically separated
electronic devices.
The Telecommunications System
 The hardware and software that transmits
information from one location to another
 Components include:
 Hardware
 Media
 Networks
 Software
 Data comm
providers
 Protocols
 Applications
Telecommunication Signals
 Analog signals
Continuous waves
Information conveyed by changing wave
characteristics (amplitude and frequency)
 Digital signals
Discrete pulses
Information conveyed in binary form (on or
off pulses)
Easily understood by computer
Communication Processors
 Hardware devices utilized in data
transmission and reception
Modem - device that converts analog signals
to digital (and vice versa); enables signal
transmission over telephone system
Multiplexor - device that transmits multiple
signals over single medium
Front-end processor – specialized computer
dedicated to managing communication tasks
The Five Characteristics of Channels
Characteristics
Description
Transmission rate
Rate at which channel carries data from one
computer to another.
Bandwidth
Volume or capacity of data that a channel can
carry.
Transmission mode
Ways by which data are transmitted. Two
ways include asynchronous (one byte at a
time) and synchronous (blocks of bytes).
Transmission direction
Three directions for transmitting data include
simplex, half duplex, and full duplex.
Transmission signals
Information travels as analog or digital
signals.
Wire-based Communication Channels
 Twisted-pair wire (telephone wire)
Cheap and easy to work with
Slow; subject to interference; low security
 Coaxial cable
Carries more data; shielded from interference
More expensive; harder to work with; low
security
Wire-based Communication Channels
(continued)
 Fiber-optic cable
Transmit information as light waves through
glass fiber
Fast; high-capacity; secure; not subject to
interference
Hard to work with
Wireless Communication Channels
 Microwave
High capacity; inexpensive relative to wire
Requires line of sight transmission towers;
subject to environmental interference
 Satellite
Very high capacity; large coverage area
Expensive; propagation delay; requires
encryption for security
Wireless Communication Channels
(continued)
 Radio
Suitable for short distance communication;
inexpensive; easy to install; high speed
Interference problems; insecure
 Cellular radio technology
 Infrared
Understanding Communication
Media
 Transmission speed
 Bandwidth – the range of frequencies available in a
channel
 More bandwidth, more channel capacity
 Transmission mode
 Character by character (asynchronous)
 Streams of characters (synchronous)
 Transmission accuracy
 Accuracy controls added to messages
 Error detection and correction required
Telecomm Carriers and Services
 Telecomm carriers – provide telecomm
technology and services for data
communication
Common carriers – long-distance phone
companies
Value-added carriers – provide private
telecomm systems and services for a fee
Telecomm Carriers and Services (continued)
 Telecomm services
 Switched lines – transmission is routed along path to
destination
 Dedicated lines – continuous connection is established
 Wide-area Telecomm Service (WATS) – lower cost
long distance telephone service
 Integrated Services Digital Network (ISDN) – high
speed data transmission over existing phone lines
 Digital Subscriber Lines (DSL) - high speed digital
transmission over existing phone lines
Network Basics
 Network – the communication devices,
media, and software needed to connect
two or more computer systems.
 Local area networks (LANs) – a network
that spans a relatively small geographic
distance
 Wide area networks (WANs) – network
that spans a large geographic distance
Network Topology
There are three popular network topologies:
Bus topology
Ring topology
Star topology
Alternative LAN Topologies
Bus Topology
 A network configuration in which all
computers on the network are
connected through a single circuit,
such as twisted-pair cable. Messages
are transmitted to all computers on
the network, although only the
targeted device responds to the
message.
Ring Topology
 A network configuration in which
computers are arranged in the form
of a ring using twisted-wire, coaxial
cable, or fiber optics. Messages are
transmitted in one direction to all
devices between the sending node
and the receiving node.
Star Topology
A topology in which a central
host computer receives all
messages and then forwards the
message to the appropriate
computer on the network.
Local Area Networks
 Connect computers and other devices
enabling resource sharing
 Variety of topologies can be used, each
with performance strengths and
weaknesses
 Several LANs can be connected via bridges
 LANs can be connected to external
networks via gateways