Transcript for networks

Chapter 6
Information Technology in Business:
Telecommunications and Networks
• Telecommunications is the movement of information
between two devices over a distance
– Information includes data, audio, video, graphics
• Networks are collections of devices (nodes) that can
engage in telecommunications
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1. Four Basic Improvements
Telecommunications brought to Business
• Telecommunications has improved business in four main
ways:
– Better communication
– Higher efficiency
– Better distribution of data
– Instant transactions
• Modern business could not be conducted without
telecommunications
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2. Home Networks
• Connecting to the Internet from home
– Dialup connection with a modem
– Digital Subscriber Line (DSL)
– Cable connection from a cable TV company
– Satellite connection
– Fixed wireless
• The middle three connections are referred to as
broadband connections because of their high speed and
ability to carry multiple channels simultaneously (e.g.,
voice and data)
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Dialup Modem Connection
• Requires a telephone modem, network software, and
Internet service provider (ISP)
• Uses the phone line to connect to the Internet
• Ties up the phone line while on the Internet; no
incoming or outgoing calls
• Slowest type of connection (56 KBPS)
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DSL Connection
• Requires a DSL modem, network software, and within
a specified distance from a phone company installation
• Often the phone company is the ISP (BellSouth)
• Internet access is through the telephone line
• Information traveling over the phone line can be split
so that voice communication is not disrupted (you don’t
need a separate phone line for your Internet
connection)
• Speeds range from 128 KBPS – 1500 KBPS
• Line is not shared (security) and always on
• Various forms of DSL
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Cable Connection
• Requires a cable modem, software, and access to cable
TV provider
• Receive information from the cable connection send
information via phone line; Newer systems use cable
for both directions
• Cable modem separates TV signals from Internet data
• Speeds are comparable to DSL speeds
• Always-on connection
• Not private since information is shared over the cable
connection into your neighborhood; transmission
speeds diminish with many users
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Satellite Connection
• Requires a satellite modem, software, satellite dish, and
satellite provider
• Receive information from the satellite connection,
sends information via phone line; Newer systems use
satellite for both directions
• Receiving speeds 200 KBPS-400 KBPS
• Same company that offers DirectTV offers DirectPC
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Fixed Wireless
• Alternative where cable or DSL is not available
• Customer must install a microwave transceiver on roof
(no wiring required)
• Repeaters (from the telecom provider) pick up signals
and transmit them to a base station
• Transmission rates range from 2 Mbps to 100 Mbps
• Growing market
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3. Business Networks
• Why network? Sharing
– Hardware, software, and files
– Communication and collaboration applications
• Client/Server networks are networks in which one or
more computers are servers and provide services to
other computers called clients.
– Servers are usually powerful computers with large
storage systems (high end PC or minicomputer)
– Clients are usually PCs or laptops
– Print servers, file servers, Web servers
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Client-Server Applications
• Client-server networks are examples of distributed
processing because the processing for a given
application is split between the server and client
• Types of processing in an application
– Processing for presentation of information (user
interface)
– Processing of logic or business rules (calculations)
– Processing related to data management (storing and
retrieving data)
• Several ways that this processing is split
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4. Telecommunications Systems
Components
• Computers to process information
• Terminals that send or receive data
• Communications channels that carry the data between
the devices in the network (channels use different
media)
• Communications processors that perform specific tasks
in the transmission process
• Communications software which controls input and
output activities and other functions
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(1) Computers and Channels
• Channels are the links over which data are transmitted
from one node to another
• Data moves through the channel in the form of
electromagnetic signals or pulses of light
• Computer signals are digital
• Parts of the telephone network require analog signals
• Conversion of the signals (modems)
• Media that provide channels
– wire
– wireless (electromagnetic spectrum)
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(2) Mediums for Channels
• Wire mediums
– twisted pair
– coaxial cable
– fiber optic (each strand carries one signal)
– Next generation optical networks (multiple data
streams over a single strand)
• Wireless transmissions
– terrestrial microwave
– satellite microwave (GEO)
– low-orbit satellites (LEO)
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Characteristics of Communication
Channels
• Transmission speed through a medium is measured in
bits per second (BPS)
• The frequency of a signal is the number of times a
signal makes a complete cycle in a given time period. If
the time period is one second, then the frequency is
measured in Hertz (Hz).
• The greater the frequency of a signal the higher the
transmission speed. Conversely high transmission
speeds require higher frequencies.
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Channels and Media
Figure 6.7 Characteristics of channel media
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Bandwidth and Media
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Transmission Speed
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Sample Calculations
• Suppose you wanted to download the movie Jurassic
Park. In compressed form it would contain about 4*109
bytes or 32*109 bits. If you had a typical 28.8 Kbps
modem, how long would it take to download the movie?
• Answer: 32*109 bits/ 28.8*103 bits/sec
= 1.11*106 sec or
= 1.11*106 sec/3.6* 103 sec/hour
= 926 hours or
= 926 hours/ 24 hours/day
=12.86 days
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(3) Components: Special Communication
Processors
• Front-end processor - a special computer that manages
the communications tasks for the host
• Controller - a device that supervises communications
between the CPU and other peripheral devices
(terminals and printers) in a network
• Multiplexor - a device that enables a single
communications channel to carry data signals from
multiple sources simultaneously
• All of these devices can be considered special purpose
computers
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Location of a Multiplexor
Figure 6.9 Multiplexing
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Other Networking Hardware
• Network Interface Card - a circuit board required by
any device that will connect to a network (wired or
wireless)
• Hub – device used to connect several devices to a
network
• Switch – a more intelligent hub
• Bridge – a device for connecting two dissimilar
networks (a LAN to the Internet)
• Router – a more intelligent bridge
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(4) Components: Communications
Software
• Special software is required for telecommunications; it
resides in the host, front-end processor, or other special
processors
• Communications software for the PC at home
• Systems software (for networks)
– network operating systems (NOS)
– security software
– Network management software
• Application software for networks
– Email software
– Client/server applications (FrontPage)
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5. Types of Networks (Topology)
• Star -central host, all communication must pass
through the host
• Ring - all computers are linked by a closed loop; data
passes from one node to the next in one direction; no
central host
• Bus - a single circuit links a number of devices; data is
broadcast to the entire network; if one machine fails
none of the other machines are effected
• Tree – consists of several stars connected to form a tree
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Network Topology
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Types of Network (Geographic Scope)
• Local networks
– PBX
– LANs
• Large networks
– WANs
– VANs
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Local Networks: PBX
• A PBX (Private Branch Exchange) is special purpose
computer designed to do the switching for a firm’s
internal phone network
• Modern PBX can carry both voice and data
• Advantages - no special wiring, expandable, vendor
support
• Disadvantages - limited geographic scope, cannot
handle high volumes of data (e.g., video)
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Local Networks: LANs
• Local area network - a network that requires its own
cabling and encompasses a limited distance (one or two
buildings); nodes are usually PCs and peripherals
• Advantages
– handle high volumes of data
– sharing of hardware, software, files, and data
– unique application (email, video conferencing, online applications)
• Disadvantages
– expandability
– vendor support or internal expertise
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Large Networks: WAN
• Wide area networks nodes
• Corporations can build their own or using
communications service providers
• Switched and dedicated lines
• Individual firm assumes significant role in
telecommunications management
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Large Networks: VANs
• Value-added networks are private data-only networks
that provide economies in service cost and network
management because they are used by many firms
• Value-added means that customers do not have to
invest in network equipment and management
• Disadvantage
– loss of control/expertise
– Security
• General Electric is a company that provides a VAN
• An example of a Web based EDI product
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Virtual Private Network
• A combination of private and public lines offered by a
telecom provider to allow customers, employees, and
suppliers to access a firm’s private network (intranet)
via the Internet. Use of a VPN creates an “extranet.”
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The link between the private network and the Internet
is often referred to as a tunnel
• “Virtual” refers to the illusion that the use is accessing
a private network directly.
• Heavily used in supply chain management
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6. Protocols
• Protocols are rules and procedures (virtually
languages) that govern the transmissions between
components (devices) in a single network or between
two networks
• Important protocols
– TCP/IP (Internet protocols)
– HTTP (Internet protocol)
– Ethernet (LAN protocol)
– Token passing (LAN protocol)
– ANSI X12 and EDIFACT (EDI protocols)
– Open systems interconnection or OSI (WAN
protocol)
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7. Characteristics of Telecommunication
Signals and Network Capabilities
• Serial versus parallel
• Directions of signals (simplex, half-duplex, full duplex)
• Types of signals (analog versus digital)
• Timing of signal transmissions (asynchronous versus
synchronous)
• Switching techniques (circuit and packet switching)
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Serial Versus Parallel Transmissions
• In serial transmissions one bit is transmitted after
another in a stream of bits over a single line
– On PCs modems and mice use serial transmission
– Serial ports
• In parallel transmissions more than one bit is
transmitted simultaneously (usually an entire byte is
transmitted along a bundle of parallel lines)
– On PCs information sent to your printer employs
parallel transmissions
– Parallel ports
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Data Communications (Cont.)
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Three Modes of Communication Between
Devices
• Simplex
• One-way in one direction
• Radio and television
• Half-Duplex
• One-way in two directions
• Walkie-Talkie, CB radio
• Older connections between terminals and computers
• Full-Duplex
• Both device can transmit and receive simultaneously
• Telephones
• Communication between modern computers
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Analog vs. Digital Signals
• Analog signals
• A continuous series of waves
• Like a sine curve
• Digital signals
• A series of discrete bits
• Modulation is the transformation of digital signal to an
analog signal
• Demodulation is the transformation of an analog signal
to a digital signal
• Role of a modem
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Timing of Communication Between Devices
• In asynchronous communication data is transmitted in
a serial manner without concern of a special timing aid
(clock). Most communication between computers and
devices is asynchronous -- it can occur at any time and
at irregular intervals.
– Overhead bits: start, stop, and parity bits
• In synchronous communication, transmissions between
devices are governed by a timing device. Large blocks
of bits can be transmitted at regular time intervals.
Communications within the CPU and memory are
usually synchronous.
– Much lower overhead but requires expensive timing
devices
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Communication Modes
Figure 6.4 Synchronous transmission
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8. Switching Techniques
• Circuit switching sets up a dedicated path between two points in a
network. For the duration of the communication no other
transmissions may use this circuit and all transmissions follow the
dedicated path.
– The telephone system links together media segments to create a
single unbroken line for each telephone call.
– Not very efficient for large volumes of data
• In packet switching all data are packaged into fixed-sized packets
that make their way to the destination over many different paths.
– The Internet uses packet switching
– Very efficient for sending large amounts of data
• New Internet protocols will make the Internet viable for telephone
calls
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9. Wireless Technologies
• Wireless technologies are of interest to business because
they eliminate the need for expensive cables and enable
mobility
• Wireless standards (or Wi-Fi) apply to mobile devices
(laptops, PDA, cell phones)
– Family of standards IEEE 802.11 (the 11 stands for the max bit
rate supported, 11 Mpbs)
– Most popular is 802.11b which operates in the 2.4-2.5 GHz
range
– Enables spread spectrum communication (the transmitting
device transmits over several frequencies so that if one
degrades you can switch to another
– Transmission range is about 300 ft (distance is likely to
increase)
– To make a device wireless requires that the device contain a
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wireless card
Wireless Networks
• In order to communicate with a network using a
wireless device, you must be close enough to an access
point (AP). The access point is a device that is
connected to a wired network.
– If a household has a wired connection to the
Internet (cable or DSL) then wireless devices can
access the Internet by acquiring a wireless router
(an AP) that is connected to your cable or DSL
modem. This enables all your wireless devices to
link to the Internet.
– Public access points are often called hotspots.
Winthrop has several hotspots on campus
– Cell phones with dual circuitry
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Other Wireless Issues
• Wi-Fi networks are much cheaper to install than
stationary LANS
• Wi-Fi networks can be extended by adding additional
access points
• Wi-Fi networks are susceptible to interference from
other devices
• Bluetooth is another wireless networking standard for
creating small private networks
• The Wi-Fi standard (802.11b) is easily penetrated by
outsiders with appropriate hardware and software
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