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GATE 2023 CS – Question 52

Computer Networks · Application Layer: DNS and HTTP · 2 marks · Multiple select

Suppose in a web browser, you click on the www.gate-2023.in URL. The browser cache is empty. The IP address for this URL is not cached in your local host, so a DNS lookup is triggered (by the local DNS server deployed on your local host) over the 3-tier DNS hierarchy in an iterative mode. No resource records are cached anywhere across all DNS servers. Let RTT denote the round trip time between your local host and DNS servers in the DNS hierarchy. The round trip time between the local host and the web server hosting www.gate-2023.in is also equal to RTT. The HTML file associated with the URL is small enough to have negligible transmission time and negligible rendering time by your web browser, which references 10 equally small objects on the same web server. Which of the following statements is/are CORRECT about the minimum elapsed time between clicking on the URL and your browser fully rendering it?

  1. 7 RTTs, in case of non-persistent HTTP with 5 parallel TCP connections.
  2. 5 RTTs, in case of persistent HTTP with pipelining.
  3. 9 RTTs, in case of non-persistent HTTP with 5 parallel TCP connections.
  4. 6 RTTs, in case of persistent HTTP with pipelining.

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Correct answer: (C) 9 RTTs, in case of non-persistent HTTP with 5 parallel TCP connections.; (D) 6 RTTs, in case of persistent HTTP with pipelining.

Explanation

DNS takes 3 RTT (root, TLD, authoritative), then TCP setup 1 RTT and the HTML request 1 RTT, giving 5. Persistent HTTP with pipelining fetches all 10 objects in 1 more RTT, total 6. Non-persistent with 5 parallel connections needs 2 batches × 2 RTT = 4 more, total 9.