计算机网络代写 | COMS3200/7201 Computer Networks I

QUESTION 1
(14 marks total) {Quantitative Comparison of Packet Switching and Circuit Switching}
Consider the two scenarios below: a circuit-switching scenario in which Ncs users, each requiring a bandwidth
of 10 Mbps, must share a link of capacity 50 Mbps. A packet-switching scenario with Nps users sharing a 50
Mbps link, where each user again requires 10 Mbps when transmitting, but only needs to transmit 30 percent
of the time.
(a) (2 marks)  When circuit switching is used, what is the maximum number of circuit-switched users that can
be supported?
For the remainder of this problem, suppose packet switching is used.
(b) (2 marks) Suppose there are 10 packet-switching users (i.e., Nps = 10). What is the probability that a given
(speciÑc) user is transmitting, and the remaining users are not transmitting?
(c) (3 marks) What is the probability that one user (any one among the 10 users) is transmitting, and the
remaining users are not transmitting?
(d) (3 marks) What is the probability that any 6 users (of the total 10 users) are transmitting and the
remaining users are not transmitting?
(e) (4 marks) What is the probability that more than 4 users are transmitting?

QUESTION 2
{HTTP GET}
Suppose that a server receives the following HTTP GET message from a client browser:
GET /main/test1.html HTTP/1.1 \r\n
Host: www.uq2.edu.au \r\n
User-agent: Firefox/3.6.12 \r\n
Accept: text/html, application/xhtml+xml \r\n
Accept-language: en, fr; q = 0.8, en-nz; q =0.5 \r\n
Accept-Encoding: gzip, deflat \r\n
Connection: close \r\n
\r\n
(a) (2 marks) What is the name of the Ñle that is being retrieved in this GET message? Please use Ñle name
only.
(b) (2 marks)  What version of HTTP protocol does the browser use? Please use only number.
(c) (2 marks)  What is the language preference of the browser user mostly prefers to use?
(d) (2 marks)  Does the browser want to have persistent connections? Answer Yes, No or Undecidable.
(e) (2 marks)  Assume that the browser has received “internal server error” from the web server. What is
response code for it? Please provide the numerical value.