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CIT 307 Online Data Communications

CIT 307 Online Data Communications. Digital Transmission. Kevin Siminski, Instructor. Module 5. Linecoding. Characteristics Line Coding Schemes Other Schemes. Line Coding. Signal level versus data level. DC Component. Lack of synchronization. Why is timing important?.

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CIT 307 Online Data Communications

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  1. CIT 307 OnlineData Communications Digital Transmission Kevin Siminski, Instructor Module 5

  2. Linecoding • Characteristics • Line Coding Schemes • Other Schemes

  3. Line Coding

  4. Signal level versus data level

  5. DC Component

  6. Lack of synchronization

  7. Why is timing important? In a digital transmission, the receiver clock is 0.1 percent faster than the sender clock. How many extra bits per second does the receiver receive if the data rate is 1 Kbps? How many if the data rate is 1 Mbps?

  8. Why timing (continued)? • At 1 Kbps: • 1000 bits sent 1001 bits received1 extra bps • At 1 Mbps: • 1,000,000 bits sent 1,001,000 bits received1000 extra bps

  9. Line Coding

  10. Unipolar Encoding Unipolar encoding uses only one voltage level.

  11. Unipolar Encoding

  12. Polar Encoding Polar encoding uses two voltage levels (positive and negative).

  13. Polar Encoding

  14. Polar encoding In NRZ-L the level of the signal is dependent upon the state of the bit. In NRZ-L the level of the signal is dependent upon the state of the bit.

  15. NRZ-L & NRZ-I encoding

  16. RZ encoding

  17. Synchronization A good encoded digital signal must contain a provision for synchronization. Timing/synchronization is one of the most important elements in Layer 1

  18. Bi-polar Encoding In bipolar encoding, we use three levels: positive, zero, and negative. This is the most common encoding mechanism used in North America transmission systems

  19. Bi-polar AMI encoding

  20. Data transmission

  21. Parallel Transmission

  22. Serial Transmission

  23. Asynchronous Transmission Asynchronous here means “asynchronous at the byte level,” but the bits are still synchronized; their durations are the same.

  24. Asynchronous Transmission

  25. Synchronous Transmission In synchronous transmission, we send bits one after another without start/stop bits or gaps. It is the responsibility of the receiver to group the bits.

  26. Synchronous Transmission

  27. Important point to consider • Timing/Synchronization is the single most important element in a data communications network. • Encoding transforms 0’s & 1’s into electronic pulses. • The North American standard used today is Bi-Polar encoding

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