Grading scheme

Problem 2

Question 1

• 1/4 point per correctly listed socket.
• 1/8 point if the computer is correct but not the socket type.

Question 2

• 1 point for correctly listing packet 12.
• 1/2 point for correctly listing each of the other packets.
• An incorrectly listed source or destination socket costs 1/4 point.
• An incorrectly listed source or destination computer costs all points for the given packet.

Question 3

• 1/2 point for correct DNS lookup roundtrip.
• 1/2 point for correct TCP connection-setup roundtrip.
• 1/2 point for correct HTTP GET request delay.
• 1/2 point for correct propagation delay for HTTP response.
• 1 point for correct transmission delay for HTTP response.

Question 4

• 3 points for correctly and completely specifying a scenario (partial credit below).
• 3 points for the actual delay computation:
• • 1/2 point for DNS lookup.
  • 1/2 point for TCP connection-setup.
  • 1/2 point for correct HTTP GET request delay.
  • 1/2 point for correct propagation delay for HTTP response.
  • 1 point for correct transmission delay for HTTP response.

• 0.5/3 if the student says it is the max(download image1, download image2) and does not state any assumption regarding queueing delay.
• 1.5/3 if the student says it is the max(download image1, download image2) and clearly state that this holds only if we assume there is no queuing delay.
• 1/3 if the student takes a maximum but does not properly state the assumption regarding queueing delay
• 1.5/3 if the student takes a maximum but only states: assume there is no queuing delay.
• 3/3 if the student takes download image 2 as the maximum and properly states the assumption that switch 1 (or Bob) received the last bit of the first image before the first bit of the second (or something close to this).

• 1/3 if the student takes the response time of GET cmu image as the max, but does not mention queueing delay or only assume there is no queueing delay.
• 2/3 if the student takes the response time of GET cmu image as the max. But, uses reasoning about no queueing delay. Example, he/she says there is no queuing delay because the cmu logo is bigger and the path from cmu has R as the bottleneck; which is slower than that on ucal (2R).
• 2.5/3 if the student takes the response time of GET cmu image as the max, and shows that there is no queueing delay through computation. But, forgets about the transmission delay of the ucal logo at switch 1 in the computation.
• 3/3 if the student takes the response time of GET cmu image as the max, and correctly shows that there is no queueing delay through computation.

• 0/3 if the student sums the download time of both images.
• 0/3 if the student assumes that the ucal.logo image is at cmu.

Question 5

• 1 point for mentioning DNS.
• 1 point for mentioning caching/TTLs.
• 3 points for saying that Céline will consider how long it takes to resolve www.berkeley.edu.
• 1 point for saying that Céline will have previously estimated how long it takes to resolve a DNS name that’s already cached.

Question 6

• 1 point for saying it’s the IP address (or both the IP address and the time difference).
• 1/2 point for saying it’s the time difference.
• 2 points for any reasonable explanation. Examples: proxy web server, DNS cache poisoning, DNS stale mapping.

Question 1 

2 points for:

• R x 4D
• R x RTT
• 1000 MSS (in case one of them takes into account flow control)
• The min of 1000 MSS and either R x 4D or R x RTT.

Question 2

• 1 point got 1000 MSS.

Question 3

• 3 points for 1000 MSS / 4D (or 1000 MSS / RTT).
• 3 points for R.
• 3 points for min(1000MSS/4D, R).
  
• 2 points for 1000 MSS/2D but the student seems to have the right idea in mind.

Question 4

• 4 points for 999 ACKs.
• 1 point for anything else that seems reasonable.

Question 5

• 4 points for 2 MSS / (4D + 2 Timeout)
• 4 points for 2 MSS / (RTT + 2 Timeout)
• 1 points for not answering but showing some correct understanding of the question.
• 1.5 point for showing some correct understanding and providing an incorrect but somewhat plausible formula.

Question 6

• 3 points for saying they will be in the application-layer header.
• 2.5 points for saying they will be in the application-layer message.
• 1 point for saying they will be in a cookie.