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?

DNS Lookup Time:

• The 3-tier DNS hierarchy consists of the Root DNS server, TLD DNS server (.in), and Authoritative DNS server (gate-2023.in).

• With iterative queries and no caching:

  $$\text{DNS time} = 1\text{ RTT (Root)} + 1\text{ RTT (TLD)} + 1\text{ RTT (Authoritative)} = 3\text{ RTT}$$

Base HTML Retrieval:

• $1\text{ RTT}$ for TCP connection establishment.

• $1\text{ RTT}$ for the HTTP GET request and receiving the base HTML file.

Referenced Objects Retrieval:

• Non-persistent HTTP with 5 parallel connections:

  • To fetch 10 objects using 5 parallel connections requires 2 consecutive rounds.

  • Each round takes $1\text{ RTT}$ (TCP handshake) $+ 1\text{ RTT}$ (HTTP request/response) $= 2\text{ RTT}$.

  • Total time for objects $= 2 \times 2 = 4\text{ RTT}$.

  • Total elapsed time $= 5\text{ RTT} + 4\text{ RTT} = 9\text{ RTT}$. Thus, (C) is correct and (A) is incorrect.

• Persistent HTTP with pipelining:

  • The persistent connection is already established, so all 10 requests are pipelined together over the existing connection and retrieved in $1\text{ RTT}$.

  • Total elapsed time $= 5\text{ RTT} + 1\text{ RTT} = 6\text{ RTT}$. Thus, (D) is correct and (B) is incorrect.