Question 1 128 pts] Suppose Alice\'s web browser needs to download a web page of
ID: 3861909 • Letter: Q
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Question 1 128 pts] Suppose Alice's web browser needs to download a web page of 5 Kbytes (HTML file size). Consider the network throughput between Alice and the web server to be 5 Mbps (for both upload and download), and propagation delay of 0.1 seconds within Alice's ISP, and 0.5 seconds between Alice's host and any host outside her ISP. Assume instantaneous processing at the server and client and negligible transmission delay for TCP and HTTP messages if without entity body. a) (7 pts) Suppose that Alice's web browser does not know the IP address of the web server. Please, write down the resource record (ignore the ttl field) for www.pierowebit, which has address 192.115.70.8, that is stored in three authoritative DNS servers, dns1.pieroweb.it, dns2.pieroweb.it, dns3.pieroweb.it, which have addresses 192.115.70.8, 192.115.70.9, 192.115.70.10, respectively Write down the resource records that would be contained in the TLD "it" servers to allow the translation of the web server address www.pierowebit (suppose no DNS caching when contacted by Alice's web browser b) Compute the total time it takes for Alice to receive the web page (including the DNS address resolution based on what said in a) c) (7 pts) Suppose that the web page has references to 5 other web objects of 5Mbytes each to be visualized in the page. How long does it take to Alice's browser to retrieve all objects and visualize the web page in case it is configured to use a non-persistent connection? Would Alice save time by utilizing a persistent connection with pipelining? How much would save?Explanation / Answer
A machine is known by its IP address. Resolving machine names into numbers is the responsibility of Domain Name Service.
To resolve, it is required for the machine to know the IP address of a computer. The host file is queried and if the answer is found in the host file, the answer is returned.
If the domain name is specified, then the PC queries this machine.
When PPP connection is made, tell the machine where it can get hostname to IP number so that the machine names can be used but the computer can translate these to IP addresses.
The resource record has the following information:
b) The total time it takes for Alice to receive the web page (including the DNS address resolution based on what said in a)) is as follows:
The throughput of the network = 5Mbps = 5 * 10^6 bits per second
Size of web page = 5 Kbytes = 5* 10^3 bytes
Time of propagation = size of web page / throughput = (5*10 ^3)/(5*10^6) = 10^-3 seconds = 1msec
The propagation delay within Alice's ISP = 0.1 sec
The propagation delay between Alice's host and any other host outside her ISP = 0.5 sec
Total time = 0.1 + 0.5 + 0.001 = 0.601 seconds
c) If the web page has references to 5 other web objects of 5Mbytes each to be visualized in the page. The time taken by Alice's browser to retrieve all objects and visualize the web page in case it is configured to use a non-persistent connection is the same as calculated above as it does not depends on the web objects.
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