W5 acceptable 4 4 5 6 7 acked 5 5 5 2 3

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Unformatted text preview: eat •  Receiver passes data to app in order, and buffers out- of- order segments to reduce retransmissions •  ACK conveys highest in- order segment, plus hints about out- of- order segments •  TCP uses a selec7ve repeat design; we’ll see the details later 204 Sliding Window – Selec7ve Repeat (2) •  Buffers W segments, keeps state variable, LAS = LAST ACK SENT •  On receive: –  Buffer segments [LAS+1, LAS+W] –  Pass up to app in- order segments from LAS+1, and update LAS –  Send ACK for LAS regardless 205 11 11/4/13 Sliding Window – Retransmissions •  Go- Back- N sender uses a single 7mer to detect losses –  On 7meout, resends buffered packets star7ng at LAR+1 •  Selec7ve Repeat sender uses a 7mer per unacked segment to detect losses –  On 7meout for segment, resend it –  Hope to resend fewer segments 206 Problem •  Sliding window uses pipelining to keep the network busy –  What if the receiver is overloaded? Arg … Streaming video Big Iron Wee Mobile 213 12 11/4/13 Sliding Window – Receiver •  Consider receiver with W buffers –  LAS=LAST ACK SENT, app pulls in- order data from buffer with recv() call Sliding Window W=5 5 5 5 .. 5 6 7 5 Acceptable 5 2 3 high 3 .. Finished Too .. LAS seq. number 214 Sliding Window – Receiver (2) •  Suppose the next two segments arrive but app does not call recv() W=5 Acceptable .. 5 6 7 5 5 5 5 5 2 3 high 3 .. Finished Too .. LAS seq. number 215 13 11/4/13 Sliding Window – Receiver (3) •  Suppose the next two segments arrive but app does not call recv() –  LAS rises, but we can’t slide window! W=5 Acceptable...
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