Data Communication Grade 11 Chapter 4 pg 71

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Data CommunicationGrade 11 Chapter 4pg 71

• (NETWORKING)

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What is Data Communication?

• Has three main components
• Sender ( source)
• Medium ( Communication channel)
• Receiver
• The Sender/Receiver would be two computers that
  could communicate through telephone lines, cables
  or the air (microwaves)
• Can transmit data, text, sound, graphics or
  video

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Basic Concepts

• When looking at transmitting data the following
  must be considered
• Physical Connection this will influence the
  number of bits that can be transmitted
  simultaneously.
• Timing whether the sender and receiver must be
  synchronized
• Direction of data flow

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Physical Connection- Parallel Communication

• Simultaneous transmission
• Usually computer to printer
• Short distances only fast communication

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Physical Connection - Serial Communication

• Serial transmission ( one by one behind the
  other)
• Transmission to serial hardware devices e.g Mouse
• Longer distance than parallel
• Has two modes
• Asynchronous
• Synchronous

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Typical IEB question

• 1.Explain the difference between serial and
  parallel communication. Use examples

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Timing - Asynchronous transmission

• Characters sent as a single string
• Also referred to as start stop transmission
• Useful when transmission occurs at irregular
  intervals user typing
• Used in Low speed I/O devices serial printer /
  modems

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Timing - Synchronous transmission

• Data transferred in blocks controlled by
  electronic clock pulses
• Synchronous characters are placed at beginning
  and end of a data block
• Timing between sender and receiver is
  synchronized
• Transmission occurs at fixed intervals and fixed
  rates.
• Network transmission is normally synchronous

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Direction
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What is a computer network?

• A group of computers or computing devices (
  also called nodes ) that are connected together
  by some kind of communication medium.

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What is a network? Cont.

• A node can be any of the following
• Microcomputer
• Mainframe computer
• Terminal
• Printer
• Any other unit that is capable of logical
  processing

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Components of a network

• Networks include Hardware and Software the
  essential components are
• Network devices e.g computers , printers
• Communication channels, e.g cables
• Network interface cards (NIC)
• Network Software
• Hubs

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Network Hardware
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Types of Networks

• LAN - ( Local Area Network)
• Short distances, belongs to one company, school
  or organization.

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Types of Networks

• MAN (Metropolitan Area Network)
• Network that covers an entire city
• WAN ( Wide Area Network)
• A network that is spread over a wide area, such
  as across provinces or countries.

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Reasons for networking

• Reduction of Capital expenditure ( COST)
• Centralization of data
• Improved communication and sharing of information
• Security
• Networks save time, improve productivity and save
  money

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Network AdministrationThe person responsible to
administer the network is called the administrator

• Adding Users
• Deleting Users
• Creating Groups
• Issuing the correct security rights to users
• Setting up printers and managing their use across
  the network

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Network Administration The person responsible to
administer the network is called the administrator

• Installing new applications software on the file
  server
• Providing security to prevent loss of data
• Running daily backups
• Installing anti-virus software
• Monitoring the system performance
• Restoring and checking system if a power failure
  occurs

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Network Administration The person responsible to
administer the network is called the administrator

• Documenting the network to help keep track of any
  changes
• Documentation should include
• A physical diagram of the network
• Network hardware and software
• Number of licenses
• A history of problems and solutions

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Physical layout of a network (Topology)

• Bus Topology
• A common cable connects all the computers.
  Terminators are placed on either end of this
  common cable

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Physical layout of a network (Topology)

• Star Topology
• Every computer is connected via a point to point
  link to a central HUB

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Physical layout of a network (Topology)

• Ring Topology
• All machines are connected in a closed ring
  formation

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Physical layout of a network (Topology)

• Mixed (hybrid) Topology
• Combination of the other three topologies

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Typical IEB question

• 1. Give the most appropriate term for the
  following expressions
• 1.The physical layout of a network
• 2. 2.Describe the essential features of the
  following network topologies bus, star and ring.
  Make use of diagrams to illustrate your answers

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Media / Cable
Different types of media are used within a
network the type of media used will be
determined by the network topology, size etc.
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Cabling

• UTP
• Uses RJ45 connector

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Cabling

• STP
• Uses IBM Universal Connector

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Cables

• Coaxial Cable
• Uses BNC (British Navel Connector) with a
  terminator on last connection

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Cabling

• Fiber optic cable

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Typical IEB Question

• 1.        Compare a bus and a star topology with
  respect to the following
• (a) Cabling type and cost 2
• (b) Cost of additional network components
  4
• (c ) Reliability 2
• (d) Security 2
• (e) Performance 2
• 2. Which topology (star or bus) would you
  recommend based on your
• comparisons in above. Briefly motivate
  your decision. 3

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Media Access Method

• When there are many computers connected in a LAN,
  there must be rules so that the messages are
  transmitted in an orderly manner
• Media Access Method means that computers will
  be given a fair chance to communicate over a
  network

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Token Passing Access Method

• Only one station can transmit at any given time
• A token travels from one workstation in the
  network to another

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CSMA / CD access methodCarrier-Sense
Multiple-Access with Collision Detection

• Workstations may send a message when ever they
  want.
• No single computer has control
• A situation where all computers can transmit
  simultaneously on a line is called
  broadcasting.

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EthernetIEEE 802.3 specification

• Rules
• Can use either Bus or a Star topology
• Any of three media
• Twisted pair, coax, fibre
• Access Method
• CSMA/CD
• Runs at a rate of 10mbps
• Fast ethernet
• Extension of ethernet
• Supports rates of 100mbps
• Uses cat 5 UTP or Fiber Optic
• Gigabit Ethernet
• Supports rates of up to 1 gigabit per second

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Token Ring IEEE 802.5 specification standard

• Robust Reliable Network
• Uses a Ring Topology
• Uses a concentrator called a MSAU (Multi Station
  Access Unit)
• Access method Token Passing
• Can be configured to transmit
• at either 4 or 16 mbps
• Can use STP, UTP, and coaxial cables Fibre
  optic can be used for the main access path

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Typical IEB questions

• 1. Describe the essential features of the
  following
• 2. Token rings
• 3. What is a token ring
• 4.  Name the media access method used in a token
  ring
• 5. Explain how this media access method works

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FDDIFibre Distributed Data Interface

• Ring Based Network
• Implemented without hubs
• Devices called concentrators can be used to do a
  similar function
• Uses token passing media
• More than one token can simultaneously circulate
• It provides data transport at 100 mbps
• Fast reliable network
• Used as a backbone

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Computer roles within a LAN

• Clients
• Use but do not provide network resources
• Servers
• Only provide network resources
• Peers
• Computers that both use and provide network
  resources

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Peer to Peer networking
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Server based networking
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Protocols

• A communication method used between two computers
• Computers must have the same protocols to be able
  to communicate

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Protocols

• Examples of protocols
• TCP/IP (Suite of protocols

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Protocols

• NETBeui
• IPX/SPX

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Types of Servers

• File Server
• Dedicated to storing and managing files
• Print Servers
• Computers that manage printing

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Types of Servers

• Network Servers
• Manage network traffic
• Web Servers
• Serve or deliver web pages

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Server Types Cont.

• Proxy Server
• Servers that sit between clients application such
  as web browsers and a file server
• To enhance performance of internet by caching web
  pages
• For security hacking can normally only break
  into the proxy
• To filter requests blocking sites etc.

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Types of Servers Cont.

• Application Servers
• Clients can use the extra computing power and
  expensive software that are stored on a shared
  computer

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Server Types

• Message Servers
• Provide messages to computers in a network
• Includes electronic mail and groupware services

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CD Servers

• CD Servers
• Looks like very large, fast hard drives and are
  accompanied by sophisticated software that allows
  many users to access the information stored on
  them.
• Used in multi-Media environments
• Stores up to 35 full CDs (dependent on size of
  server)

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Network Terminology

• EMI Electro magnetic Interference
• Electronic Interference on a cable
• Attenuation
• Weakening of a signal over distance
• Crosstalk
• Magnetic fields in two wires that are close to
  one another can interfere with transmission

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Network Terminology

• Packet
• Grouping of information been sent over the
  network
• Eavesdropping
• Related to EMI. Possible for people to access the
  signal