计算机网络代考 | Computer Networks & Applications COMPSCI 3001, 7039

本次澳洲代考主要为计算机网络相关的限时测试

Application Layer
Question 1
(a) What information is used by a process running on one host to identify
a process running on another host?
[2 marks]

(b) Why does HTTP run on top of TCP rather than on UDP?
[2 marks]

(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)?
[3 marks]

(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-
width.

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-
lations).
[12 marks]

(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;
NF
us +PN
i=1 ui
)
Explain what each of the following terms represents (for example:
“The time for one peer to download a single copy of the file”)
1. F=us
2. F=dmin
3. us +PN
i=1 ui
[3 marks]
ii. Using the same variables (F, u, d) give an equation for the mini-
mum download time for a client/server file download.
[3 marks]