The IP address for the associated URL is not cached in your local host, so a DNS

Question

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 an RTT of RTTi,..., RTTn. Further suppose that the Web page associated with the link contains exactly one object, consisting of a small amount of HTML text. Let RTTn 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? Now suppose the HTML file references eight very small objects on the same server. Neglecting transmission times, how much time elapses with Non-persistent HTTP with no parallel TCP connections? Non-persistent HTTP with the brow ser configured for 5 parallel connections? Persistent HTTP?

Explanation / Answer

The total amount of time to get the IP address is

RTT1 + RTT2 +---+ RTTn .

Once the IP address is known, RTTo elapses to set up the TCP connection and another RTTo elapses to request and receive the small object. The total response time is

2RTTo +RTT1 +RTT2 +---+RTTn

a. RTT1 +---+RTTn+ 2RTTo +8. 2RTTo=18RTTo + RTT1+---+ RTTn .

b) RTT1 +---+RTTn+ 2RTTo +2.2RTTo=6RTTo + RTT1+---+ RTTn .

c)RTT1 +---+RTTn+ 2RTTo +RTTo=3RTTo + RTT1+---+ RTTn .

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