Data Communications _ Computer Networks by wuyunqing

VIEWS: 29 PAGES: 62

									Data Communication
        &
Computer Networks



                     1
Uses of Computer Networks
     (for Companies)

   •   Resource sharing
   •   High reliability
   •   Saving money
   •   Scalability
   •   Communication medium
                              2
      Resource Sharing
Goal is to make all
         programs
         equipments &
         data
available to anyone on the network
without regard to the physical location
of the resource and the user.
                                      3
          High Reliability

• Multiple copies of files
• Multiple CPUs
For military, banking, air traffic control,
nuclear power plant, and many other
applications, the ability to continue
operating in the face of hardware
problem is of utmost importance.          4
         Saving Money
• Small computers have a much
  better price/performance ratio
  than large ones.
• Mainframes are faster than PCs but
  they cost a thousand times more.

Mainframes      Client – Server Systems


                                     5
          Client – Server Model
  Client Machine             Server Machine
                   Request
                                              Server
                                              Process
                   Reply

Client
Process

                   Network


                                                       6
                   Scalability

Centralized Mainframes      Client – Server Systems

should be replaced by       • new clients and
a large one.                • new servers

• expensive                 can be added as needed.
• disruption to the users

                                                7
Uses of Computer Networks
        (for People)

• Access to remote information
• Person-to-person communication
• Interactive entertainment


                              8
        Telecommunication

Communication of information by electronic
       means over some distance




                                             9
   Telecommunication Components

• Computers
          » to process information



• Input output devices
          » to send or receive data

                                      10
   Telecommunication Components
• Communications channels
           » links between sending and receiving
             devices to transmit data

• use various transmission media

        – telephone lines, coaxial cables, twisted wire

         cables, fiber optic cables, and wireless media

                                                          11
Telecommunication Components
• communications processes
     • modems, multiplexes, NICs
     • provide support functions


• communications software
       – control communication


                                   12
        Twisted wire cables


•   consisted of pairs of twisted copper wire

•   used for both analogue and digital
    transmission

•   low in cost

•   low in transmission speed               13
         Twisted wire cables
Useful for local and wide are networks




                                         14
             Coaxial Cable

• A thick insulated copper wire

• Can transmit large volumes of data quickly

• Faster and more interference free medium

• Speed up to 200MB per second

• Cannot support analogue phone
                                               15
  conversations
Coaxial Cable




                16
            Fiber optic cable
• Consists of strands of clear glass fiber

• Has the thickness of a human hair

• Data are transformed into pulses of light

• Rate 500kb – several trillion bit per second

                                                 17
           Fiber optic cable

• Faster lighter and more durable than wire

  media

• Suitable to transfer large volumes of data

• More expensive

                                               18
            Fiber optic cable
• Difficult to work with
• Harder to install
• Used for backbone cabling
  – that handle the major traffic
     • a primary path

• No delays and no degradation in quality
                                            19
Fiber optic cable




                    20
        Wireless transmission
• Sends signals through air or space

• Technologies include
  – microwave transmission
  – communication satellites
  – pagers
  – cellular phones
  – smart phones
                                       21
  – PDAs
               Microwave
                         Wireless transmission

• High frequency radio signals are transmitted

  trough the atmosphere from one

  transmission station to another



                                           22
             Microwave
• A high volume

• long distance

• point – to – point transmission method




                                           23
                Smart phone
• Wireless phone with
  – voice
  – text and
  – internet capabilities




                              24
25
Personal Digital Assistant (PDA)
•   Small
•   pen –based
•   handheld computer with
•   built in wireless telecommunications
Wireless networks and devices can be
more expensive, slower and more error
prone

                                           26
27
     Computer Communication
           Schematic
Computer A             User-to-user             Computer B
                       communication
 Application                                     Application
 process                                         process


                     Computer-to-computer
Communication        communication              Communication
subsystem                                       subsystem

            Computer-to-network communication

                 Data communication network
                                                               28
      Network Hardware

Criterions for classifying networks:

    • Transmission technology
    • Scale


                                   29
Transmission Technology


 • Broadcast networks

 • Point-to-point networks



                             30
                      Scale
Interprocess Processors     Example
or distance located in same
   0.1 m     Circuit board   Data flow machine
     1m      System          Multicomputer
   10 m      Room
  100 m      Building        Local area network
    1 km     Campus               ( LAN )
   10 km     City            Metropolitan area
                             network ( MAN )
   100 km    Country         Wide area network
 1,000 km    Continent            ( WAN )
10,000 km    Planet          The Internet
                                                  31
    Network Topologies
•   Bus topology
•   Start topology
•   Ring topology
•   Fully connected topology
•   Combined topologies

                               32
          Bus Topology
     Mainframe                 File server




Workstation      File server            Workstation



                                                      33
      Bus Topology (cont.)
• A single communication line
• Each device has an interface that listens to
  the bus and examines its data traffic
• Carrier Sense, Multiple Access with
  Collision Detection (CSMA/CD)

Ethernet (IEEE 802.3)
           - One popular bus network             34
Star Topology

    Cables




    Computer
                35
           Ring Topology
Computer




              Cables




                           36
Fully Connected Topology



            Cables




 Computer
                           37
Geographic scope classification




   LAN           WAN




                              38
 Local Area Networks ( LANs)

They are widely used to connect
personal computers & workstations in
company offices & factories to
share resources & exchange information.


                                       39
 Local Area Networks (LANs)
• Link local resources
  – computers and terminals
  – Printers and Scanners, etc
  – Files and programs

in the same department or building of a firm
          Sharing local resources
                                               40
  Local Area Networks (LANs)

• Encompasses a limited distance
  – usually one building or several buildings in
    close proximity


• Mostly within 2000 foot radius


                                                   41
 Local Area Networks (LANs)
• Link computers and computer controlled
  machines in a factory




                                           42
  Local Area Networks (LANs)
• Often controlled and operated by
  – end user groups or
  – departments in a firm


• Require own communications channels


                                        43
   Network Operating System
            (NOS)
• Software that

  – manages communications
  – coordinate Network resources

             on the network



                                   44
                     WAN

• Span over broad geographical distance

  – Ranging from
     • several miles to
     • entire continents



                                          45
 Wide Area Network (WAN)
• May consists of
       – a combination of
           » switched and dedicated lines

       – variety of
          » cable
          » satellite and
          » microwave technologies


                                            46
WAN




      47
      Other Network Services
                           Circuit switching

• A direct connection
  – between two nodes in a Network
  – For the duration of the transmission

           must be maintained


                                           48
49
  Network Communication
• Circuit-Switched
         (Connection Oriented)
• Packet-Switched
         (Connectionless)



                                 50
Circuit-Switched Communication
 Needs: Dedicated connection

 Advantage : Capacity guaranteed

 Disadvantage: High cost

 Example : Telephone Systems
                                   51
Packet-Switched Communication
 Needs      : Few connections
Advantage   : Multiple communications
              among computers can
               proceed concurrently
Disadvantage: Cannot guarantee the
               network capacity

   Usually used to connect computers
                                         52
     What is a “Packet”?
A packet is a single unit, or "package",
of data that is sent across a network.

Types of data that are sent across the
 Internet using packets include:
 E-mail messages
 Files
 Web pages

                                           53
             A Packet
Header
   Sender”s address
   Receiver’s address
Data or Body
   Data
Footer
  To show end of packet
  Error correction


                          54
             Packet switching

• Breaks up a lengthy block of data into small
   fixed bundles called packets



                      Data bits
                           Address and packet number bits
Error checking bits
                                                     55
          Packet switching
• A packet may contain
  – data bits
  – error checking bits
  – and destination address specifying bits

        Divided into separate sections



                                              56
           Packet switching

• Packets can be routed

  – in different paths

  – in different communication channels




                                          57
Packet switching




                   58
         Types of signals
                            Analogue signal

• A continuous waveform that passes through
 a communications medium

• Used for voice communication



                                         59
Analogue signal




                  60
         Types of signals
                        A digital signal


• A discreet waveform




                                      61
                Modem

• Convert analogue signals into digital signals
  and vice versa




                                            62

								
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