Question

Suppose within your web browser you click on a link 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 given IP address. Further suppose that 3 DNS servers are visited before your host receives the IP address form DNS. The round trip time between the client and the ithDNS server is Ti(1≤i≤3), and that between the jthDNS server and the (j+1)thDNS server is tj(1≤j≤2). Further suppose that thepage contains four objects (including the webpage) and that the web browser has to fetch the webpage (the .html file) before it knows 3 (other) image objects are contained in the webpage. Assume that it takes negligible time to transmit the .html file (i.e., the transmission time for the file is zero), but Oitime is required to transmit the ithimage object. Let T0denote the propagation delay (i.e., RTT excluding transmission time) between the local host and the server containing the objects.How much time elapses from the time instant when the client clicks on the link until the time instant when the client receives a complete webpage? Assume iterative DNS query service and persistent HTTP with pipelining.

Answer 1

T1+ T2 +t1 + T3 + t1 + t2(DNS Server Time) +To(for TCP connection) + 4*To(to fetch 4 objects) + O1+O2+O3(to fetch images)