Problem 3 Consider N users trying to download a web page containing a small HTML
ID: 3718168 • Letter: P
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Problem 3 Consider N users trying to download a web page containing a small HTML file (i.e., size negligible) referencing a data file of F bits from a web server through the network shown in Fig. 1. Suppose the internal links have abun- dant bandwidth, and the edge links have bandwidth shown in the figure. Ignore DNS query delays. u: server upload d: user i download file, size F bits erver network with abundant bandwidth 4, u; user i upload capacity Figure 1: Problem 3 illustration. a) Suppose N = 1 (only one user). The path from the user to the server has a round-trip delay of RTT seconds and a throughput of u, bps. How long does it take for the user to download the web page using non-persistent HTTP? [2 pt] How about using persistent HTTP? 12 pt of downloading the data file to the completion of downloading at the last user, under: client-server architecture [2 pt] and P2P architecture [2 pt. c) Give the numerical answer for b) for F = 100M bits, N = 3, us-211 bps, dy d2 ds 10M bps, uu 1M bps, us 2M bps. [2 pt)Explanation / Answer
a.)Since persistent one connection for all data for one round trip times. Only 2 messages will be saved
Therefore the number of RTT is 3 for 3 images and 2 ( one each for start and close connection )
b) Note that each downloaded object can be completely put into one data packet. Let Tp denote the one-way propagation delay between the client and the server. First consider parallel downloads via non-persistent connections.
The parallel download would allow 10 connections share the 150 bits/sec bandwidth, thus each gets just 15 bits/sec.
Thus, the total time needed to receive all objects is given by: (200/150+Tp + 200/150 +Tp + 200/150+Tp + 100,000/150+ Tp ) + (200/(150/10)+Tp + 200/(150/10) +Tp + 200/(150/10)+Tp + 100,000/(150/10)+ Tp ) = 7377 + 8*Tp (seconds) Then consider persistent HTTP connection.
The total time needed is give by: (200/150+Tp + 200/150 +Tp + 200/150+Tp + 100,000/150+ Tp ) + 10*(200/150+Tp + 100,0
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