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Bab 2

Bab 2. Hardware Building Blocks :. Nodes: Assume general-purpose (programmable) computers; e.g., workstations. Sometimes replaced with special-purpose hardware. Finite memory (implies limited buffer space) Connects to network via a network adaptor Fast processor, slow memory.

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Bab 2

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  1. Bab 2

  2. Hardware Building Blocks : • Nodes: Assume general-purpose (programmable) computers; e.g., workstations. Sometimes replaced with special-purpose hardware. • Finite memory (implies limited buffer space) • Connects to network via a network adaptor • Fast processor, slow memory

  3. Hardware Building Blocks • Links: analog – digital; half – full duplex Sometimes you install your own

  4. Hardware Building Blocks • Sometimes leased from the phone company

  5. Encoding A. Overview • Signals propagate over a physical medium. • Digital signals • Analog signals • Data can be either digital or analog; we're interested in digital data.

  6. Problem: Encode the binary data that the source node wants to send to the destination node into the signal that propagates over to the destination node

  7. Non-Return To Zero (NRZ) • Problem: Consecutive 1s or 0s • Low signal (0) may be interpretted as no signal • High signal (1) leads to baseline wander • Unable to recover clock

  8. Non-Return To Zero Inverted (NRZI) Make a transition from the current signal to encode a one, and stay at the current signal to encode a zero; solves the problem of consecutive ones. • Manchester Transmits the XOR of the NRZ encoded data and the clock; only 50% efficient.

  9. 4B/5B • Idea: Every 4 bits of data is encoded in a 5-bit code, with the 5-bit codes selected to have no more than one leading 0 and no more than two trailing 0 (i.e., never get more than three consecutive 0s). • Resulting 5-bit codes are then transmitted using the NRZI encoding. • Achieves 80% efficiency.

  10. Framing • A. Overview • Problem: Breaking sequence of bits into a frame • Must determine first and last bit of the frame • Typically implemented by network adaptor • Adaptor fetches (deposits) frames out of (into) host memory

  11. Byte-Oriented Protocol • Sentinel approach : a) BISYNC b)IMP-IMP • Byte Counting Approach : DDCMP • Bit-Oriented Protocol • Clock-based Framing

  12. Error Detection

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