Suppose you click on a link within your Web browser to obtain a Web page. The IP address for the associated URL is not cached in your local host, so a DNS look-up is necessary to obtain the IP address. Suppose that n DNS servers are visited before your host receives the IP address from DNS; the successive visits incur an RTT of RTT1, RTT2 ... RTTn.
Further suppose that two images, sized 100KB and 80KB respectively, are embedded in the Web page associated with the link, while the size of the Web page is 4KB. Let RTT0 denote the RTT between the local host and the server containing the object, and let R denote the average end-to-end transmission rate between your computer and the Web server.
How much time elapses from when the client clicks on the link until the client receives both the Web page and the two images?
Since nothing is specified about the unit of R (the average end-to-end transmission rate), this solution assumes that R is specified in KB/sec.
Time taken to receive the IP address from DNS = Time taken to visit the n DNS servers = RTT1 + RTT2 + ... ...
Solution shows step-by-step computation. Since nothing is specified about the unit of R (the average end-to-end transmission rate) in the question, this solution assumes that R will be specified in KB/sec.