MIT16_36s09_lec17

MIT16_36s09_lec17 - MIT OpenCourseWare http://ocw.mit.edu...

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Unformatted text preview: MIT OpenCourseWare http://ocw.mit.edu 16.36 Communication Systems Engineering Spring 2009 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms . 16.36: Communication Systems Engineering ARQ Protocols: Stop & Wait Eytan Modiano Slide 1 Automatic Repeat ReQuest (ARQ) When the receiver detects errors in a packet, how does it let the transmitter know to re-send the corresponding packet? Systems which automatically request the retransmission of missing packets or packets with errors are called ARQ systems. Three common schemes Stop & Wait Go Back N Selective Repeat Byzantine Army Problem Byzantine failure: the failure to correctly execute a step in an algorithm Eytan Modiano Slide 2 Pure Stop and Wait Protocol ACK Time -----> NAK packet 0 CRC packet 1 CRC packet 1 CRC arrival times at receiver Transmitter departure times at A Packet 0 Packet 1 Accepted Accepted Problem: Lost Packets Sender will wait forever for an acknowledgement Packet may be lost due to framing errors Solution: Use time-out (TO) Sender retransmits the packet after a timeout Eytan Modiano Slide 3 The Use Of Timeouts For Lost Packets Requires Sequence Numbers <---- timeout ----->...
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This note was uploaded on 11/07/2011 for the course AERO 16.38 taught by Professor Alexandremegretski during the Spring '09 term at MIT.

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MIT16_36s09_lec17 - MIT OpenCourseWare http://ocw.mit.edu...

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