1. ECE6610 Explanations for PA 1 and PA 2
Sandeep Kakumanu

2. PA 1: Problem Definition
Setup two ftp flows over TCP.
Study different flavors of TCP – Tahoe, Reno, New Reno, Sack.
Study Loss behavior.

3. PA 1: Problem Definition (cont’d)
Find end-to-end throughput, and SD.
Plot instantaneous throughput and CWND on same graph.
Introduce wireless losses and understand TCP behavior.

4. PA 1: Solutions (a) Flavor Avg Throughput (Kbps) SD of Throughput
TCP Tahoe
893
72.5
TCP Reno
927
387
TCP New Reno
928
500
TCP Sack
900
374

5. PA 1: Solutions (b)

6. PA1: Solutions (c)

7. PA 1: Solutions (Summary)
TCP New Reno is the most efficient.
TCP Tahoe is the fairest.
All TCP flavors suffer from losses. Any random loss is treated as congestion loss. Hence they perform badly under wireless conditions.

8. PA 2: Problem Definition
Construct static wireless network of 10 nodes in 500mx500m grid.
Understand the MAC behavior of three protocols: CSMA, MACA and
Study UDP, TCP behavior in these networks.
Study performance under different loss conditions.
Metrics to study: mean and SD of throughput; mean and SD of end-to-end delay.

9. PA 2: Solutions (a)

10. PA 2: Solutions (b)

11. PA 2: Solutions (c)

12. PA 2: Solutions (d)

13. PA 2: Solutions (e)

14. PA 2: Solutions (f)

15. PA 2: Solutions (Summary)
performs poorly for UDP. This is because of ACK recovery and subsequent backoff. RTS/CTS causes further reduction in capacity.
CSMA on the other hand does not have overheads.
Delay performance of is erratic because of retransmissions. CSMA is not reliable.
TCP performance under high losses is better with because of recovery.