5 6 7 2 2 unacked 5 2 3 3 acked unavail

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Unformatted text preview: RTT (=2D) –  Pipelining improves performance –  Need W=2BD to fill network path 196 Sliding Window Protocol •  Many varia7ons, depending on how buffers, acknowledgements, and retransmissions are handled •  Go- Back- N » –  Simplest version, can be inefficient •  Selec7ve Repeat » –  More complex, beker performance 199 8 11/4/13 Sliding Window – Sender •  Sender buffers up to W segments un7l they are acknowledged –  LFS=LAST FRAME SENT, LAR=LAST ACK REC’D –  Sends while LFS – LAR ≤ W Sliding Window W=5 Available 2 3 .. 3 Unacked .. 5 6 7 .. 2 3 4 5 Unavailable .. Acked LAR LFS seq. number 200 Sliding Window – Sender (2) •  Transport accepts another segment of data from the Applica7on ... –  Transport sends it (as LFS–LAR à༎ 5) W=5 4 2 3 .. 3 Unacked .. 5 6 7 .. 2 3 4 5 Unavailable .. Acked LAR LFS seq. number 201 9 11/4/13 Sliding Window – Sender (3) •  Next higher ACK arrives from peer… –  Window advances, buffer is freed –  LFS–LAR à༎ 4 (can send one more) W=5 Available 3 4 .. .. 5 6 7 2 2 Unacked 5 2 3 .. 3 .. Acked Unavail. LAR LFS seq. number 202 Sliding Window – Go- Back- N •  Receiver keeps only a single packet buffer for the next segment –  State variable, LAS = LAST ACK SENT •  On receive: –  If seq. number is LAS+1, accept and pass it to app, update LAS, send ACK –  Otherwise discard (as out of order) 203 10 11/4/13 Sliding Window – Selec7ve Rep...
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This document was uploaded on 04/04/2014.

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