Deadline 2 hours from now (2 pm) a) 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 an RTT of RTT1, RTT2, …, RTTn. Further suppose that the Webpage associated with the link contains exactly one object, consisting of a small amount of HTML test. 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? • Suppose the HTML file references four 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. Persistent HTTP? b) Below is a portion of a possible DNS database for cs.vu.nl. Give you understanding of the function of the following resource record. And give explanation of the meaning for each field in this resource record. www.cs.vu.nl 86400 IN CNAME star.cs.vu.nl • What is a whois database? • Use various whois databases on the internet to obtain the names of two DNS servers. Indicate which whois databases you used. • Use nslookup on centralops.net/co to send DNS queries to DNS servers with the IP address of a public google DNS for a domain name. Try querying for Type A, NS, and MX reports. List a record of each query and explain the meaning of the resource record you have listed. c) TCP and UDP are transport layer protocols. (a) What is Round Trip Time (RTT)? Do you need to set a timer for data transmission using UDP? Give your reasoning. (b) Consider the TCP procedure for estimating RTT. Suppose that we use exponential weighted moving average (EWMA) for estimating RTT using formula: EstimatedRTT(n) = (1- )*EstimatedRTT(n-1) + *SampleRTT(n-1), The margin is estimated by formula: DevRTT(n) = (1-)*DevRTT(n-1) + *|SampleRTT(n-1)-EstimatedRTT(n-1)|, Where n is the transmission round. Suppose that  = 0.25,  = 0.3. Let initial Estimated RTT at transmission round 3 be 90 ms, let estimated margin DevRTT at transmission round 4 be 15 ms. The observed SampleRTT at transmission round 3 is 75ms, the observed SampleRTT at transmission round 4 is 95ms. What is the Estimated RTT at transmission round 5? What is the Estimated margin DevRTT at transmission round 5? If the TCP timeout interval is set using the formula TimeoutInterval(n) = EstimatedRTT(n) + 4* DevRTT(n), what is the TimeoutInterval for transmission round 5 (round to the nearest integer)? d) The UDP checksum provides for error detection. Suppose that we have the following 16-bit words: Word 1: 1100000011001100 Word 2: 0110000000000110 Word 3: 1011011001101100 Question: What is the checksum field in the UDP segment, if the three words are transferred via UDP? Explain in detail how you obtain your result