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Information System Networks


Title: Chapter 6 Subject: Information System Networks and the Internet Author: XZetera Communications Description: Business & Information Systems 2/e by: Robert C ... – PowerPoint PPT presentation

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Title: Information System Networks

Chapter 6
  • Information System Networks
  • and
  • the Internet

Communications Hardware
  • Two main types of communications hardware
  • Communications channel the link over which data
    is transmitted
  • Communications processors provide processing
    capabilities between the computer and the
    communications channel

Communications Hardware
  • Communications channel characteristics
  • Data is transmitted over the channel as bits.
  • Each bit is sent one after the other.
  • Bits are grouped to form bytes that represent
    characters using ASCII, EBCDIC, Unicode or some
    other code.

Communications Hardware (contd.)
  • The way in which bits are sent determines two
    main characteristics of the channel
  • Signal type
  • Data rate

Signal Type
  • Bits can be sent either as
  • An Analog signal data is transmitted by a wave
    pattern that varies continuously
  • A Digital signal data is transmitted as a
    series of high and low pulses
  • The human voice is analog
  • Telephones are analog
  • Computers are digital

Data Rate
  • Data rate is measured as bits per second (bps).
  • Bandwidth also describes how much data can be
    transmitted over a channel in a given period of

Data Rate (contd.)
  • Baud rate refers to the maximum number of changes
    that can occur per second in the state of a
    communication channel (changes in a communication
    signal). The data transmition rate for a
    communication channel is equal to the baud rate
    for that channel times the number of bits that
    can be sent with each change in the state of that
    communication channel.

Data Rate
  • Broadband refers to an analog communications
    method that splits an analog communication
    channel in to multiple communication channels.

Data Rate
  • Broadband ISDN (B-ISDN) Refers to a digital
    communication method that split a digital phone
    line in to multiple communication channel.
  • Basic Rate ISDN (BRI) provide 2 channels each
    with 64000 capacity.
  • Primary Rate ISDN (PRI) provide 23 channels with
    64000 bps capacity.
  • ISDN Is an acronym for Integrated Services
    Digital Network.

Types of Communications Channel Media
  • Wire cables sometimes called copper cables
    have been used since the 1800s.
  • Two main forms
  • Twisted-pair wiring
  • Coaxial cable

Communications Channel Media (contd.)
  • Twisted-pair wiring
  • Two insulated copper wires twisted together
  • Most telephone lines are twisted-pair
  • Can also be used for data
  • Data transmission rate is slow compared to other

Communications Channel Media (contd.)
  • Coaxial cable
  • Copper wire insulated with rubber and plastic.
  • Used with cable television systems.
  • Data transmission rate is faster than
    twisted-pair, and more expensive, but slower than
    other media.

Communications Channel Media (contd.)
  • Fiber-optic cables
  • Bundles of glass or plastic fibers.
  • Each fiber is 1/2000 inch thick about the size
    of a human hair.
  • Data is transmitted by a laser that pulses light
    through the fiber.
  • Data transmission rate is very fast.

Communications Channel Media (contd.)
  • Microwave (wireless)
  • Special types of radio signals sent from one
    microwave antenna to another.
  • Transmission is line-of-sight, i.e, one antenna
    must be able to see the other.
  • Two types
  • Land based antenna approximately 30 miles
  • Satellite positioned 22,300 miles in space
    geosynchronous orbit.

Communications Channel Media (contd.)
  • Other wireless media
  • Infrared spectrum
  • Very short distances
  • Relatively slow

Communications Processors
  1. Channel interface devices
  2. Communications control units
  3. Protocols converter devices
  4. Communications security devices

I. Channel Interface Devices
  • Modems convert digital signals to analog
    signals at the origin and reverse the process at
    the destination of the signal.
  • Digital to analog is MOdulation.
  • Analog to digital is DEModulation.
  • Modems may be either internal or external to the

I. Channel Interface Devices (contd.)
  • Modem data rates are typically 33 Kbps to 56
  • Cable modems (cable Adaptors) are devices to
    provide the interface between a computer and a
    cable systems data transmission capability.
  • For ISDN or Digital Subscriber Line (DSL) digital
    modems (terminal adapters) is required.

II. Communication Control Units
  • Multiplexer combines signals from several
    slow-speed devices to transmit over a high speed
  • Front-End Processor is a computer that sits
    between the channel and the main computer (host
    computer) and is dedicated to performing
    communication functions.

III. Communications Protocols
  • Protocols, settings, standards, or parameters are
    the rules that must be followed when computers
    communicate with one another to avoid errors.
  • Computers that wish to communicate and have
    different protocols must use a code converter and
    protocol converter to standardize their
  • Code conversion (conversion among ASCII, EBCIDIC,
  • Protocol conversion

IV. Communications Security
  • A problem with data communications is the lack of
    security over a communications channel. One way
    of solving this problem is to use data encryption
    to convert the data to an unintelligible form for
    transmission and to return it to an intelligible
    form at the destination.
  • Decryption (decoding) requires a key.
  • Asymmetric key cryptolography
  • Public key (for encription) private key (for

Communications Software
  • Communications software is required to control
    communications between computers. It receives
    data from communications processors connected to
    the channel and passes the data to other software
    in the computer for processing.

Communications Software (contd.)
  • Types of communications software
  • Multi-user processing environment
  • Terminal emulators
  • Telecommunications monitor

Communications Software (contd.)
  • Client server processing environment requires
    Network Operationg System (NOS) which establishes
    and maintains the communication between the nodes
    (workstations and the file server)
  • File server software
  • Client software (workstation software) as used
    in client/server computing
  • Light client (Web browser)
  • Heavy client (Traditional client programs that
    where proprietary, expensive to maintain)

Network Topologies
  • Star network each node is connected to a
    central node.
  • Hierarchical network organized like a family
    tree. Each computer communicate with other
    computers through a common node.
  • Bus network each node is connected to a single
    communication channel.
  • Ring network each node is connected to a common
    channel forming a loop.

Types of Networks
  • Local Area Network (LAN)
  • Wide Area Network (WAN)
  • Metropolitan Area Network (MAN)
  • Internetwork connected networks

Local Area Networks
  • Local Area Network Structure
  • Connection Topology
  • Star, ring, Hierarchical, Bus, Hybrid
  • Communications channel
  • wired and Wire less
  • Require Network Interface Cards (NIC) in each
    device on the network
  • Permits sharing of resources
  • Protocol is Usually either Ethernet (carrier
    sense multiple access with collision detection
    (CSM,CD)), Token Ring (token passing) or Polling.

Wide Area Networks
  • Connection Topology.
  • Star, Hierarchical, or hybrid
  • Communications channel.
  • Any Type of media because of they use common
    carriers or telecommunications companies
  • (packet switching, circuit switching, and frame
  • Permits sharing of resources.
  • Can include a Virtual Private Network (VPN).

  • It is a public international network
  • Grew slowly at first and exploded in 1993 with
    the adoption of the Hyper Text Markup Language
    (HTML) standards for the World Wide Web (WWW).
  • Two protocols
  • Transmission Control Protocol (TCP)
  • Internet Protocol (IP)
  • Most users require a relationship with an
    Internet Service Provider (ISP).

Intranets and Extranets
  • An Intranet is an Internet like network but
    access is restricted to within a business or
  • Firewalls are used to control access to an
  • An Extranet permits controlled outside access to
    an Intranet like network.

Hardware and Software
  • Requires the business have a web site.
  • The web software runs on a web server which has
    special e-commerce software.