Archive for category midterm
1-7: E D C B X D B
8. 28 ms; 4 ms; 0 ms; 36 ms
9. (1100,1200) or (1100,1300); Timer starts after first ACK, timeout, retransmit 1100. Receive ACK 1300, start another timer, timeout, retransmit 1300. Receive ACK 1400. Done.
We have the following re-grade policy for CS2105 midterm.
- Your midterm scripts will be returned during tutorials or office hours.
- You should check through your script on the spot, and if you think you deserve more marks than is awarded, you are entitled to request for a re-grade.
- We reserve the right not to accept a re-grading request once the test script leaves the room.
- If you ask your friend to pick up the script on your behalf, then you are giving up your rights to request for a re-grade (unless your friend is doing it on your behalf).
- Re-grading requests due to counting or summing errors are exceptions to the above rules.
1. Here is another attempt to explain the solution to PS3, Q5.
2. For Midterm Review, here are a few points that was raised repeatedly during Q&A and discussions:
- Passing the checksum checks does NOT guarantee that the input bits have no error. We have seen an example in the lecture, where swapping two bits in the same column resulted in the same checksum value. The answer for Q4 is X.
- What is the implication of guaranteeing the maximum RTT between S and R? If you know the maximum RTT, you can set the timeout value to be larger than D to prevent premature timeout.
3. In PS4 Q4, we say that we want the maximum RWIN to be set dynamically depending on the network conditions, to BW x RTT. This value is twice the bandwidth-delay product. Recall that BW x Propagation Delay is the bandwidth-delay product, and RTT is twice the propagation delay.
Also, note that the receiver typically allocate the buffer to be the same size as the maximum possible RWIN.
- When: 11 March, 2pm – 4pm
- Where: MPSH1, Section A
- Scope: Lecture 1-5, Problem Set 1-4, DIY Exercise 1-2
- Length: 90 mins
- Total Marks: 30 (tips for time management: for each mark, allocate 3 mins on average)
- A4-size double sided crib sheet allowed
- A calculator and a ruler are helpful.
Update: My MCQs are usually associated with the following important instructions, which were missing in the original midterm review PDF file:
For MCQ, pick the most appropriate answer and write the corresponding choice (A, B, C, D, or E) in the answer box. If multiple answers are equally appropriate, pick one and write the chosen answer in the answer box. Do NOT write more than one answers in the answer box. If none of the answers are appropriate, write X in the answer box.}
Here is the midterm review questions, selected from past CS2105 midterms and finals. No solution will be posted, but you are more than welcome to show the teaching staff your solution and discuss them with us, either online or during our office hours.