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Data Communication Basics: Hardware and Encoding Techniques

Explore point-to-point links, framing, error detection, and more in data communication. Learn about encoding methods like NRZ and Manchester to improve data integrity. Discover the importance of connection quality.

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Data Communication Basics: Hardware and Encoding Techniques

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  1. Point-to-Point Links Outline Hardware Building Blocks Encoding Framing Error Detection Sliding Window Algorithm Datacom 1

  2. Network Connections Memory latency is more important than CPU speed Datacom 1

  3. Bits 0 0 1 0 1 1 1 1 0 1 0 0 0 0 1 0 NRZ Encoding Datacom 1

  4. The Electromagnetic Spectrum Datacom 1

  5. Cables and Fiber Link Bandwidths Datacom 1

  6. Leased Line Service Bandwidth Datacom 1

  7. Services at the home Datacom 1

  8. Asymmetric Digital Subscriber Line (ADSL) Datacom 1

  9. Very high data rate DSL(symmetric) Datacom 1

  10. Wireless Links Datacom 1

  11. Wireless LANs • HIPERLAN (High Performance European Radio LAN--5.2 GHz and 17 GHz • IEEE 802.11---2.4 GHz • PICONET • Bluetooth (Ericsson, Nokia, IBM, Toshiba, Intel) • 2.45 GHz, 1 Mbps, 10 M Datacom 1

  12. Bits 0 0 1 0 1 1 1 1 0 1 0 0 0 0 1 0 NRZ Encoding Datacom 1

  13. Problem: Consecutive 1s or 0s • Low signal (0) may be interpreted as no signal • High signal (1) leads to baseline wander • Unable to recover clock Datacom 1

  14. Alternative Encodings • Non-return to Zero Inverted (NRZI) • make a transition from current signal to encode a one; stay at current signal to encode a zero • solves the problem of consecutive ones • Manchester • transmit XOR of the NRZ encoded data and the clock • only 50% efficient. Datacom 1

  15. Coding Examples Datacom 1

  16. Encodings (cont) • 4B/5B • every 4 bits of data encoded in a 5-bit code • 5-bit codes selected to have no more than one leading 0 and no more than two trailing 0s • thus, never get more than three consecutive 0s • resulting 5-bit codes are transmitted using NRZI • achieves 80% efficiency Datacom 1

  17. Bits Node A Adaptor Adaptor Node B Frames Framing • Break sequence of bits into a frame • Typically implemented by network adaptor Datacom 1

  18. 8 16 16 8 Beginning Ending Header Body CRC sequence sequence Approaches • Bit-Oriented Approach-High level Data Link Control (HDLC) • delineate frame with special pattern: 01111110 (these are sentinel strings) • problem: special pattern appears in the payload • solution: bit stuffing • sender: insert 0 after five consecutive 1s • receiver: delete 0 that follows five consecutive 1s Datacom 1

  19. Bit stuffing example • 0111111000110111011111011111101111110 Datacom 1

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