Midterm 2021, Problem 2 introduction

Consider the network in this figure:

• Each link has propagation delay Dp.
  
• For each link, the transmission rate has the value shown in the figure in each direction. 
  
• The maximum segment size (MSS) is 1000 bytes (for both the Stanford and MIT networks).
  
• switch1 and switch2 are store-and-forward packet switches with 0 processing delay.
  
• All Stanford computers use dns.stanford.edu as their local DNS server. dns.stanford.edu also acts as an authoritative DNS server for stanford.edu, and as a top-level-domain (TLD) DNS server for .edu. It performs recursive DNS requests.
  
• All MIT computers use dns.mit.edu as their local DNS server. dns.mit.edu acts as an authoritative DNS server for mit.edu. It performs recursive DNS requests.
  
• Web browsers and web servers communicate through persistent TCP connections (i.e., they reuse each established TCP connection to exchange as much traffic as possible).
  
• At the beginning of this problem, all caches (of all kinds) are empty, and there are no established TCP connections.
  
• In all questions except for Question 7, DNS records are cached for a day. 
  
• There is no other traffic on the Internet other than the traffic caused by Alice's and Bob's actions. 

• Transport-layer, network-layer and link-layer headers are insignificant (assume 0 bytes).
• Assume that packets that do not carry any application-layer data experience 0 transmission delay. E.g., TCP SYN, TCP SYN ACK, and packets that carry only TCP ACKs experience 0 transmission delay.
• Each DNS request is 50 bytes.
• Each DNS response is 100 bytes.
• Each HTTP GET request is 200 bytes.
• Each HTTP GET response is 200 bytes + the size of the requested object.
• www.stanford.edu/index.html: 800 bytes
• www.mit.edu/tech-news.mp4: 2100 bytes