Question

Please Help! thanks in advance

1. 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. Suppose that n DNS servers are visited before your host receives the IP address from DNS; the successive visits incur a RTT (round-trip time) of RTT1, … , and RTTn. Further suppose that the Web page associated with the link contains exactly one object, consisting of a small amount of HTML text. Let RTT0 denote the RTT between the local host and the server containing the object. Assuming zero transmission time of the object, how much time elapses from when the client clicks on the link until the client receives the object?

2. Referring to Problem 1, now suppose the HTML file references seven very small objects on the same server. Neglecting transmission times, how much time elapses with a. Non-persistent HTTP with no parallel TCP connections? b. Non-persistent HTTP with the browser configured for three parallel connections? c. Persistent HTTP?

Answer 1

Answer:

1).

Here, the DNS lookup is necessary and from your computer, it goes to many DNS servers and if we start from our computer, the time taken is RTT1 + RTT2 + RTTn. Here, RTT means Round Trip Time. For example, RTT1 means from your computer to first DNS server and then back to your computer.

So, total of RTT1 + RTT2 + ... + RTTn time is required when your computer is finally getting the required server address. Now, you have that address so you are querying that server directly and getting the result in RTT0 time.

As the transmission cost is neglected in the total scenario, the only time you need to consider is the round trip time.

So, for the given scenario, RTT1 + RTT2 + ... + RTTn time is used first and at last RTT0 time is used. So, the total of RTT0 + RTT1 + RTT2 + ... + RTTn time is elapsed.

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