CSCE 3612 ch8-2

CSCE 3612 ch8-2 - Networks Network-based design....

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© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Networks Network-based design. Communication analysis. System performance analysis. Internet. Internet-enabled systems. Vehicles as networks. Sensor networks
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© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Communication analysis First, understand delay for single  message. Delay for multiple messages depends on: network protocol; devices on network.
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© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Message delay Assume: single message; no contention. Delay: t m  = t x  + t n  + t r     = xmtr overhead + network xmit time + rcvr  overhead
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© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Example: I 2 C message delay Network transmission time dominates. Assume 100 kbits/sec, one 8-bit byte. Number of bits in packet: n packet  = start + address + data + stop             = 1 + 8 + 8 + 1 = 18 bits Time required to transmit: 1.8 x 10 -4  sec. 20 instructions on 8 MHz controller adds 2.5 x  10 -6  delay on xmtr, rcvr.
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© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Multiple messages If messages can interfere with each other,  analysis is more complex. Model total message delay: t y  = t d  + t m     = wait time for network + message delay
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© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Arbitration and delay Fixed-priority arbitration introduces  unbounded delay for all but highest- priority device. Unless higher-priority devices are known to  have limited rates that allow lower devices to  transmit. Round-robin arbitration introduces  bounded delay proportional to N.
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© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Further complications Acknowledgment time. Transmission errors.
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© 2008 Wayne Wolf Overheads for Computers as Components 2 nd ed. Priority inversion in networks In many networks, a packet cannot be  interrupted. Result is priority inversion:
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This note was uploaded on 09/30/2008 for the course CSCE 3612 taught by Professor Goodrum during the Fall '08 term at North Texas.

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CSCE 3612 ch8-2 - Networks Network-based design....

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