dlc_arq - ARQ Mechanisms Rudra Dutta ECE/CSC 570 - Fall...

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ARQ Mechanisms ARQ Mechanisms Rudra Dutta ECE/CSC 570 - Fall 2007, Section 001
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Copyright Rudra Dutta, NCSU, Fall, 2007 2 Need for ARQ Need for ARQ Re-transmissions are needed sometimes Flow Control Sender swamps receiver, must re-send Error Control Error recovery after detection Only non-erroneous copy at the sender But– sender needs to know that
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Copyright Rudra Dutta, NCSU, Fall, 2007 3 The Three Army Problem The Three Army Problem Acknowledgements are needed But may not be available Hence requests must sometimes be implicit
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Copyright Rudra Dutta, NCSU, Fall, 2007 4 Retransmission Strategies Retransmission Strategies A utomatic R epeat Re Q uest Scope - Link based, or end-to-end Concerns Correctness Sender and receiver must agree regarding what data is successfully transmitted, within small variation Frames must be delivered to higher layer in order, each frame exactly once, and must not deadlock Efficiency Throughput, fraction of time channel successfully used Assumptions Transmissions are eventually successful
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Copyright Rudra Dutta, NCSU, Fall, 2007 5 Sequence numbers Sequence numbers Delineated stream of bits stream of frames Successive frames have different identities However – some may be re transmitted It is the same frame How to indicate Identity must be embedded in identifiers Straightforward approach – sequence numbers Annoying detail – how high must numbers go? Finite number of bits to store such numbers Very important practically !!
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Copyright Rudra Dutta, NCSU, Fall, 2007 6 Timing Diagrams - Again Timing Diagrams - Again Diagrams showing sequence of events involved
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This note was uploaded on 03/20/2008 for the course NETWORKING 570 taught by Professor Dr. during the Fall '07 term at N.C. State.

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dlc_arq - ARQ Mechanisms Rudra Dutta ECE/CSC 570 - Fall...

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