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Reliable Transport

Reliable Transport. EE 122 Discussion 9/19/11. Announcements. Handouts and notes from discussion are posted on the course webpage Bandwidth-delay product: answer corrected Reminder: Homework-1 due today!. Questions 1 and 2. Sliding Window. Ensures the “pipe” is always full (efficiency)

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Reliable Transport

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  1. Reliable Transport EE 122 Discussion 9/19/11

  2. Announcements • Handouts and notes from discussion are posted on the course webpage • Bandwidth-delay product: answer corrected • Reminder: Homework-1 due today!

  3. Questions 1 and 2

  4. Sliding Window • Ensures the “pipe” is always full (efficiency) • Send W packets • When one gets ACK’ed, send the next one in line • If a packet times out, retransmit

  5. Individual ACKs and Cumulative ACKs • Individual ACK • Acknowledge every packet received • Loss: resend packet when k “subsequent packets” are received • Cumulative ACK • Highest packet number for which all previous packets have been received • Loss: resend missing packet upon k “duplicate ACKs” and wait for ACK

  6. Question 4a – Individual ACK A B 1 2 3 1 2 3 4 5 6 7 8 9 10 ACK-1 , ACK-2, ACK-3 1 2 3 4 5 6 1 2 3 4 5 6 7 8 9 10 ACK-4 , ACK-5, ACK-6 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 10 ACK-7 , ACK-8, ACK-9 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 ACK-10 1 2 3 4 5 6 7 8 9 10

  7. Question 4a – Cumulative ACK A B 1 2 3 1 2 3 4 5 6 7 8 9 10 CACK-upto1 , CACK-upto2, CACK-upto3 1 2 3 4 5 6 1 2 3 4 5 6 7 8 9 10 CACK-upto4 , CACK-upto5, CACK-upto6 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 10 CACK-upto7 , CACK-upto8, CACK-upto9 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 CACK-upto10 1 2 3 4 5 6 7 8 9 10

  8. Question 4b (k=1) A B 1 2 3 1 2 3 4 5 6 7 8 9 10 ACK-1, ACK-3 1 3 k=1 2 4 1 2 3 4 5 6 7 8 9 10 ACK-2 , ACK-4 1 2 3 4 567 1 2 3 4 5 6 7 8 9 10 ACK-5 , ACK-6, ACK-7 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 ACK-8, ACK-9, ACK-10 1 2 3 4 5 6 7 8 9 10

  9. Question 4b (k=2) A B 1 2 3 1 2 3 4 5 6 7 8 9 10 ACK-1, ACK-3 1 3 4 1 2 3 4 5 6 7 8 9 10 ACK-4 1 3 4 k=2 2 1 2 3 4 5 6 7 8 9 10 ACK-2 1 2 3 4 5 6 7 1 2 3 4 5 6 7 8 9 10 ACK-5, ACK-6, ACK-7 1 2 3 4 5 6 7 …

  10. Question 4b (k=2) – Why bother? A B 1 2 3 1 2 3 4 5 6 7 8 9 10 ACK-1, ACK-3 1 2 3 4 1 2 3 4 5 6 7 8 9 10 ACK-2, ACK-4 1 2 3 4 ACK-2 is delayed 5 6 7 1 2 3 4 5 6 7 8 9 10 ACK-5, ACK-6, ACK-7 1 2 3 4 5 6 7 Efficiency vs. timeliness 8 9 10 1 2 3 4 5 6 7 8 9 10 ACK-8, ACK-9, ACK-10 1 2 3 4 5 6 7 8 9 10

  11. Question 4d (k=1) – Lost ACK A B 1 2 3 1 2 3 4 5 6 7 8 9 10 ACK-1, ACK-3 1 2 3 k=1 ACK-2 is lost 2 4 1 2 3 4 5 6 7 8 9 10 ACK-2 , ACK-4 1 2 3 4 567 1 2 3 4 5 6 7 8 9 10 ACK-5 , ACK-6, ACK-7 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 ACK-8, ACK-9, ACK-10 1 2 3 4 5 6 7 8 9 10

  12. Question 4d (k=1) – Lost CACK A B 1 2 3 1 2 3 4 5 6 7 8 9 10 CACK-upto1, CACK-upto3 1 2 3 CACK-upto2 is lost 4 5 6 1 2 3 4 5 6 7 8 9 10 CACK-4 , CACK-5, CACK-6 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 10 CACK-7 , CACK-8, CACK-9 1 2 3 4 5 6 7 8 9 11 packets with Lost ACK vs. 10 packets with Lost CACK 10 1 2 3 4 5 6 7 8 9 10 CACK-10 1 2 3 4 5 6 7 8 9 10

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