Chapter 6 Telecommunications
and Networks
Chapter 6
Telecommunications
and Networks
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Presentation Overview
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The Evolution of Networking
Data Transmission Characteristics
Communications Media
Network Classifications
Network Topologies
Network Hardware
Network Software
Communications Software and Protocols
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The Evolution of Networking
Telecommunications,
combined use of
computer hardware and
communications software
for sending and receiving
information, enables
computer users
throughout the world to
communicate.
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Data Transmission
Characteristics
The transmission of data over computer
networks is characterized by the
– Rate of transmission (bandwidth)
– Type of signal (analog or digital)
– Order of bits (parallel or serial)
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Data Transmission
Characteristics
Bandwidth
– Bandwidth is the number of bits that can be transferred
per second over a given medium.
– Terms for measuring bandwidth:
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Data Transmission
Characteristics
Analog and Digital Transmission
– An analog signal is composed of continuous
waves transmitted over a medium at a certain
frequency range.
– A modem converts digital signals to analog
signals so they can be sent over telephone lines.
• Modulation – changing a digital signal into an
analog signal
• Demodulation – changing an analog signal into a
digital signal
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Data Transmission
Characteristics
Translating digital signals to analog signals
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Data Transmission
Characteristics
• An internal modem is
an electronic card
inserted into an
expansion slot on a
computer’s
motherboard.
• An external modem is
a stand-alone device
connected to the
motherboard by cable.
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Data Transmission
Characteristics
Parallel and Serial Transmission
– A parity bit is an extra bit added to a byte to
ensure there is an accurate transmission.
– In serial transmission, the byte plus the parity
bit are transmitted one bit after another in a
continuous line.
– In parallel transmission, 8 bits (a byte) plus a
parity bit are transmitted at the same time over
nine separate paths.
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Data Transmission
Characteristics
• In serial transmission, the bits are transmitted one
after the other in a line.
• In parallel transmission, the bits are transmitted at
the same time, which is faster.
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Communications Media
• A communications medium is a link that
connects computers in different locations.
• Communications media are broadly
classified as either wired or wireless.
• Wired communications use three main types
of communications media:
– Twisted-pair cable
– Coaxial cable
– Fiber-optic cable
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Communications Media
Twisted-Pair Cable
– One of the older types of communications media
– Used to connect computers in networks for transmitting
data over relatively short distances
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Communications Media
Coaxial Cable
– Used for connecting
computers in a local
computer network,
such as a network
located on a college
campus
– Used for cable
television connections
and in telephone
networks
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Communications Media
Fiber-Optic Cable
– Transmits beams of
light through a glass or
plastic core
– Is expensive and
difficult to work with
– Has very high
bandwidth
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Communications Media
Other Wired Communications Media
– Integrated Services Digital Network (ISDN)
lines are used to dial into the Internet and
receive information at high speeds.
– Digital Subscriber Lines (DSL) use existing
phone lines and new switched connections to
achieve faster speeds than traditional dial-up.
– T lines are digital, high-speed, long-distance
lines capable of carrying signals across the line.
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Communications Media
Wireless Communications Media
– Wireless communications media transmit
information as electromagnetic signals through
the air.
– Many people are embracing wireless
technologies as mobile and wireless devices
become more powerful.
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Communications Media
Microwave systems transmit data through the atmosphere
from one microwave station to another.
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Communications Media
A communications
satellite is a solarpowered, electronic
device that receives
signals from ground
transmission stations.
The satellite then
amplifies the signals and
retransmits them to the
appropriate ground
location.
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Communications Media
Infrared technology allows data in the form of light
waves to be transmitted from a special port in a
computer to an infrared sensor in a printer.
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Communications Media
With cellular technology, signals sent by cell phones
are transmitted and received from cell to cell until
they reach their destination.
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Communications Media
• Wi-Fi is a wireless local area network technology.
• Wi-Fi-enabled devices use a broadband Internet
connection through a wireless access point.
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Communications Media
Bluetooth Wireless Connectivity
– Built in to most PDAs, cell phones, and
notebook computers.
– Offers short-range connectivity with other
Bluetooth devices, forming small, temporary
networks.
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Network Classifications
• Networks can be classified by their
architecture, by the relative distances they
cover, and by the users they are designed to
support.
• Network architecture refers to the way a
network is designed and built.
Client/server and peer-to-peer are the two major
architectural designs for networks.
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Network Classifications
In client/server architecture, networked client
computers can send information to a server,
which relays information back to that
computer or to another on the network.
– Fax machines and printers are shared
resources.
– The file server provides access to a shared
hard disk.
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Network Classifications
Client/Server Architecture
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Network Classifications
In peer-to-peer architecture, computers comprising a
network have equivalent capabilities and
responsibilities—each acts as both client and server.
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Network Classifications
A local area network (LAN) is a private network that
serves an organization with computers located in the
same building or area.
LANs use a file server that houses all network resources.
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Network Classifications
A wide area network (WAN) spans a large
geographical area, connecting two or more LANs.
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Network Classifications
An intranet is a network that is housed within an
organization to serve internal users.
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Network Classifications
An extranet is an
extension of an intranet
that allows specified
external users access to
internal applications and
data via the Internet.
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Network Topologies
• Network topology is the pattern by which
the network is organized.
• Each network component is called a node.
• The most common network topologies are
bus, star, and ring.
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Network Topologies
In a bus topology, all computers are linked by a
single cable (bus) with two endpoints.
– All communications travel the length of the bus.
– A terminator is a device that absorbs signals so they
do not reflect back down the line.
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Network Topologies
In a star topology,
multiple computers and
peripheral devices are
linked to a central hub.
The hub acts as a
switching station,
sending and routing
messages accordingly.
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Network Topologies
In a ring topology there is no hub, and each computer
is connected to two or more other devices in a
circular path.
A single electronic signal, or token, is used to pass
information between computers.
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Network Hardware
• A hub is an electronic device used in older
LAN topologies to link computers and allow
them to communicate with one another.
Most manufacturers have ceased production of
hubs to focus on more powerful networking
hardware.
• A switch is a hardware device that joins
multiple computers together within one
LAN.
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Network Hardware
A repeater is a specially
designed electronic
device that receives
signals along a network,
amplifies them, and then
sends them along the
network’s
communication path.
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Network Hardware
A router is an electronic
device, usually found in
large networks (including
the Internet), that joins
two or more networks.
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Network Hardware
• A gateway is hardware and/or software that allows
communication between dissimilar networks.
• Here, the gateway is a server connecting a star
network to a ring network.
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Network Hardware
• A bridge consists of hardware and/or software
allowing communication between two similar
networks.
• This bridge connects two star networks.
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Network Hardware
• In order for a client computer to communicate
with a server or another computer it must be
connected to a network.
• Each networked client computer must contain a
network interface card (NIC).
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Network Software
• A network operating system (NOS) controls
the flow of messages from client computers
and provides services such as file access and
printing.
• Some systems, such as UNIX and the Mac
OS, have networking functions built in.
• Popular NOSs for Windows systems include
Windows Server 2003 and Windows Server
2008.
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Communications Software and
Protocols
• Communications software programs can be
used to
– Access and use the services of an Internet
service provider (ISP), such as email and use of
Web browsers
– Send and receive information to and from other
computers through LAN and WAN networks
– Send and receive faxes
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Communications Software and
Protocols
• A protocol is a set of rules and procedures
for exchanging information among
computers on a network.
• To avoid transmission errors, the computers
involved must have the same settings and
follow the same standards.
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Communications Software and
Protocols
Examples of Communication Protocol
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Communications Software and
Protocols
Almost all communications use directional
protocols to determine the flow of
transmissions among devices. There are three
possible directions:
– Simplex – data flows in only one direction
– Half-duplex – data flows in both directions,
but only in one direction at a time
– Full-duplex – data flows in both directions at
the same time
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Communications Software and
Protocols
Simplex, Half-Duplex, and Full-Duplex Directional
Protocols
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Communications Software and
Protocols
When communications are sent by asynchronous
transmission, each byte of data is surrounded by
control bits.
– The start bit signals the beginning of a character.
– The stop bit signals the end of a character.
– The parity bit checks for errors.
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Communications Software and
Protocols
With synchronous transmission, blocks of bytes are
wrapped in start and stop bytes called synch bytes.
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Communications Software and
Protocols
Local Area Network (LAN) Protocols
– Ethernet protocols specify how these
networks are set up, how devices communicate,
how problems are identified and corrected, and
how components are connected.
– Token ring protocols send an electronic signal
that can carry both a message and an address
around the ring quickly.
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Communications Software and
Protocols
Wide Area Network (WAN) Protocols
– Systems Network Architecture (SNA) uses a
polling protocol for transmitting data:
workstations are asked individually if they have
a message to transmit.
– Fiber Distributed Data Interface (FDDI) is
used for ring networks dispersed over a large
area and connected with fiber-optic cables.
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Communications Software and
Protocols
Internet and Web Protocols
– Transmission Control Protocol/Internet
Protocol (TCP/ICP) governs how packets of
data are constructed and sent to their
destinations.
– Hypertext Transfer Protocol (HTTP) is used
to transfer Web pages to computers.
– File Transfer Protocol (FTP) is used to
transmit and receive large files.
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Communications Software and
Protocols
Electronic Mail Protocols
– Simple Mail Transfer Protocol (SMTP)
determines how each message will be routed
through the Internet, and then sends the
message.
– Post Office Protocol (POP) allows the
recipient to retrieve the message.
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Communications Software and
Protocols
Wireless Application Protocols
– Wireless Application Protocol (WAP)
enables wireless devices to access and use the
Internet using a client/server network.
– 802.11 Protocol (Wi-Fi) specifies an over-theair interface between a wireless client device
and a server, or between two wireless client
devices.
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Communications Software and
Protocols
Variations of the 802.11 Protocol
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On the Horizon
Based on the information in this chapter and
your own experience, what do you think is on
the horizon?
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