GATE CS 2023 Set 1 — Question 52
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Computer Networks → Application Layer → DNS
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Question
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 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 . 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?Correct answer
(C) 9 RTT s, in case of non-persistent HTTP with 5 parallel TCP connections.; (D) 6 RTT s, in case of persistent HTTP with pipelining.
Solution
1.DNS Lookup Time:
The DNS lookup is iterative over a 3-tier hierarchy (Root, TLD, and Authoritative servers). Since no records are cached, the local DNS server (on the local host) must perform three separate queries. Each query takes . Total DNS time = s.
2.HTML Retrieval Time:
- TCP connection setup: .
- HTTP request and response for the HTML file: .
3.Object Retrieval Time:
- Case 1: Non-persistent HTTP with 5 parallel TCP connections:
- Batch 1 (5 objects): (TCP setup) + (Request/Response) = s.
- Batch 2 (5 objects): (TCP setup) + (Request/Response) = s.
Total elapsed time = (DNS) + (HTML) + (Objects) = s. (Option C is correct)
- Case 2: Persistent HTTP with pipelining:
- Request/Response for all 10 objects: .
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