all parts please Microsoft PowerPoin X HW4 I CMPEO8ON , S x HW4 1.pdf 8-01.cours

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all parts please

Microsoft PowerPoin X HW4 I CMPEO8ON , S x HW4 1.pdf 8-01.courses.soe.ucsc.edu /files/secure-attachments/HW4.1.pdf C: DNS Query Access Ti 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 lookup is necessary to obtain the IP address before retrieving the web page. Suppose that three DNS servers are visited before your host receives the IP address from the local DNS server. The first DNS server visited is the local DNS, with an RTT delay of RTTo 3 msecs. The second and third DNS servers contacted have RTTs of RTT,-40 msecs and RTT2 20 msecs. The requested Web page contains a base HTML page and no objects. Suppose the RTT between the Client and the Web server is RTTHTTP-60 msecs, i.e. it takes 60msecs for the Client to fetch the web page from the web server. Note: RTT - Round Trip Time the time to send request and receive response - inclusive, both directions) Web Server RTT?. RTT local DNS cache client With respect to the above infprmation, answer the following questions: How much time in total is spent on the DNS query? How long does it take to retrieve the web page once the URL name is resolved? How much total time elapses from when the client first clicks on the link until the client receives the web page? (Assume 0 seconds transmission time for the web page - makes the problem a. b. e. easier, but not really true for a large file!)

Explanation / Answer

a. Total time in DNS query:

Local DNS Query RTT + RTTs of the external DNS servers

Note: It is no clealry given why the second external DNS lookup is required (so all calculations assue the resolution happens only after DNS has been resolved over 3 DNS servers)

3 + 40 +20 = 63 ms

There can be a case where a quert result fromany of the external DNS servers is fully qualified result, in which case only the lower RTT will be considered

3 + 20 = 23 ms

b. Once the URL is resolved it takes exactly 60 ms to get the HTTP webpage

c. From the click of the button till the webpage is displayed, is basically the result a. + b. which can be 63 + 60 =123 ms (if it required 3 DNS) or 23 + 60 = 83 ms (if the fastest DNS results was taken)

d. As the DNS is now cached by the host, even the local DNS is not required to resolve. However to featch 1 webpage a d 4 objects, it will first donwload the webpage in 60 ms and then send back-to-back requets for 4 objects. This would take 60 + 60 ms =120 ms to complete.

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