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Outline Hardware Building Blocks Encoding Framing Error Detection Sliding Window Algorithm

Point-to-Point Links. Outline Hardware Building Blocks Encoding Framing Error Detection Sliding Window Algorithm. Network Connections. Memory latency is more important than CPU speed. Bits. 0. 0. 1. 0. 1. 1. 1. 1. 0. 1. 0. 0. 0. 0. 1. 0. NRZ. Encoding.

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Outline Hardware Building Blocks Encoding Framing Error Detection Sliding Window Algorithm

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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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