Communication System Devices


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Communication System Devices

  1. 1. Communication Devices
  2. 2. Communication History <ul><li>The Telegraph - Samuel Morse </li></ul><ul><li>The Telephone - A. Bell </li></ul><ul><li>Teletypewriter </li></ul><ul><li>Networks </li></ul>
  3. 3. Computers & Communication <ul><li>In the 1960’s people were allowed to connect their own equipment to the Public Telephone Network. </li></ul>
  4. 4. RS-232C Interface <ul><li>High speed computer communications operate on the principle of switching voltage on and off. </li></ul><ul><li>To enable devices to communicate a standard was developed to define the electrical signalling. </li></ul>
  5. 5. RS-232C Interface <ul><li>The RS-232C standard defines the function of signals as well as the physical connection. </li></ul>
  6. 6. RS-232C Interface <ul><li>The standard is for two categories of serial connection </li></ul><ul><ul><li>one for terminals (DTE - Data Terminal Equipment) </li></ul></ul><ul><ul><li>one for communications equipment (DCE - Data Communications Equipment) </li></ul></ul>
  7. 7. RS-232C Interface <ul><li>A DTE device usually connects to a DTE device </li></ul><ul><ul><li>a computer connected to a modem </li></ul></ul><ul><li>The RS-232C connection uses a 25 pin connector. </li></ul><ul><li>Some manufacturers now also supply 9 pin plugs </li></ul>
  8. 8. The Modem <ul><li>The public telephone system was designed to transmit the human voice which is an analog signal. </li></ul><ul><li>Computers exchange information using digital signals. </li></ul>
  9. 9. The Modem <ul><li>To be able to use the telephone network the digital signal must be converted to an analog signal and then back again. </li></ul>
  10. 10. The Modem <ul><li>Modem were designed to do this conversion </li></ul><ul><ul><li>i.e they MOD ulate the digital signal to analog and then DEM odulate the analog signal back to digital. </li></ul></ul><ul><li>A modem is required on both DTE devices </li></ul>
  11. 11. The Modem <ul><li>Transmission involves data compression techniques which increase the rates, error detection and error correction for more reliability. </li></ul><ul><li>The computer is connected to the modem via an RS-232C connection. </li></ul>
  12. 12. Types of Modems <ul><li>Voice/Data </li></ul><ul><ul><li>some modems can switch between voice and data modes. In voice mode it acts likes a normal telephone, while in data mode it operates like a modem. </li></ul></ul>
  13. 13. Types of Modems <ul><li>Cable Modem </li></ul><ul><ul><li>A cable modem is a device that enables the connection of a computer to a local cable TV line and receive data at a much higher rate that a normal modem. </li></ul></ul>
  14. 14. Types of Modems <ul><li>Auto-Answer Modem </li></ul><ul><ul><li>An auto-answer modem enables your computer to receive calls in your absence. </li></ul></ul><ul><li>Fax/Modem </li></ul><ul><ul><li>These types of modems can both send and receive faxes </li></ul></ul>
  15. 15. Network Interface Card <ul><li>This device acts an interface between the computer and network cabling. </li></ul><ul><li>Its function is to control data in and out of the network cabling and also moves data in and out of memory. </li></ul>
  16. 16. Network Interface Card <ul><li>It also re-arranges and buffers the data. </li></ul><ul><li>It is an expansion card that must inserted inside the computer. </li></ul>
  17. 17. Multiplexer <ul><li>This is a communication device that combines several signals together for transmission over a high speed communication line. </li></ul>MUX MUX
  18. 18. Multiplexer <ul><li>At the receiving DTE, another multiplexer (MUX) is needed to separate the signal into multiple sub channels. </li></ul>MUX MUX
  19. 19. Types of Multiplexing <ul><li>Frequency Division </li></ul><ul><ul><li>a single frequency channel is sub-divided into two or more sub-channels </li></ul></ul><ul><ul><li>used in TV broadcasting and FM radio transmission </li></ul></ul>
  20. 20. Types of Multiplexing <ul><li>Time Division </li></ul><ul><ul><li>Each node is allocated a small time frame for communication. </li></ul></ul><ul><ul><li>Each node is checked on a round-robin basis. </li></ul></ul>