(a) What information is used by a process running on one host to identify
a process running on another host?
(b) Why does HTTP run on top of TCP rather than on UDP?
(c) Consider an HTTP client that wants to retrieve a Web document at
a given URL. The IP address of the HTTP server is initially unknown.
What transport and application-layer protocols besides HTTP are needed
in this scenario (list all that will be used)?
(d) Consider a short, 10-meter link, over which a sender can transmit at a
rate of 150 bits/sec in both directions. Suppose that packets contain-
ing data are 100,000 bits long, and packets containing only control
(e.g., ACK or handshaking) are 200 bits long.
Assume that N parallel connections each get 1=N of the link band-
Now consider the HTTP protocol, and suppose that each downloaded
object is 100 Kbits long, and that the initial downloaded object con-
tains 10 referenced objects from the same sender.
Firstly, consider parallel downloads via parallel instances of non-persistent
HTTP. Secondly, consider persistent HTTP. Do you expect signiﬁcant
performance gains over the non-persistent case? Justify and explain
your answer (please clearly show your reasoning and summary calcu-
(e) i. The equation for determining the download time for a peer-to-
peer ﬁle sharing is given below.
Dp2p max(F=us; F=dmin;
Explain what each of the following terms represents (for example:
“The time for one peer to download a single copy of the ﬁle”)
3. us +PN
ii. Using the same variables (F, u, d) give an equation for the mini-
mum download time for a client/server ﬁle download.
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