Assignment#1
MMIS 653 (Fall 2014) Total points: 100 Due date: 9/20/2014 11:59PM Questions: (70 points) 1, (4 points) Is HFC transmission rate dedicated or shared among users? Are collisions possible in a downstream HFC channel? Why or why not. 2, (6 points) Suppose there are exactly two packet switches between a sending host and a receiving host. The transmission rate between the sending host and switch#1 is R1. The transmissions rate between switch#1 and switch#2 and between switch#2 and the receiving host are R2 and R3, respectively. Assuming that the switches user store-andforward packet switching, what is the total end-to-end delay to send a packet of length L? (Ignore queuing, propagation delay, and processing delay.)

3, (10 points) (a) How long does it take for a packet of length 1,000 bytes to be delivered from the sending host to the receiving host over a link of distance 4,800 km, propagation speed 2.4x108 m/s, and transmission rate 2Mbps? (b) More generally, how long does it take a packet of length L to be delivered from the sending host to the receiving host over a link of distance d, propagating speed s, and transmission rate R bps? (c) How long does it take for the first bit of the packet to arrive at the receiving host (start to count the time when the sending host starts to transmit the packet)? (d) How long does it take for the last bit of the packet to be put on the link (start to count the time when the sending host starts to transmit the packet)? 4, (8 points) Suppose Host A wants to send a large file to Host B. The path from Host A to Host B has three links, of rate R1=512kbps, R2=1.5Mbps, and R3=1Mbps. (a) Assume no other traffic in the network, what is the throughput for the file transfer? (b) Suppose the file is 8MB (consider 1MB = 106 bytes). Dividing the file size by the throughput, roughly how long will it take to transfer the file to Host B? 5, Suppose users share a 3Mbps link. Also suppose each user requires 1Mbps when transmitting, but each user transmits only 15% of the time. (See the discussion of statistical multiplexing in Section 1.3) a, (2 points) When circuit switching is used, how many users can be supported?

b, (2 points) For the remainder of this problem, suppose packet switching is used. Why will there be essentially no queuing delay before the link if three or fewer users transmit at the same time? Why will there be a queuing delay if four users transmit at the same time? c, (2 points) Find the probability that a giving user is transmitting.

6, (4 points) What information is used by a process running on one host to identify a process running on another host? 7, (4 points) Why is it said that FTP sends control information “out-of-band”? 8, (8 points) True or false? Why? a, A user requests a Web page that consists of some text and one image. For this page, the client will send one request message and receive 2 response messages. b, Two distinct Web pages (for example, www.nova.edu/resources/current_students.html and www.nova.edu/resources/faculty_staff.html ) can be sent over the same persistent connection. c, With nonpersistent connections between browser and origin server, it is possible for a single TCP segment to carry two distinct HTTP request messages. d, The Date: header in the HTTP response message indicates the time and date when the HTTP response was created and sent by the server. 9, (8 points) What is an application-layer message? A transport-layer segment? A network-layer datagram? A link-layer frame? 10, (4 points) What is the difference between network architecture and application architecture? 11, (4 points) For a communication session between a pair of processes, which process is the client and which is the server? 12, (4 points) Why do HTTP, FTP, SMTP, and POP3 run on top of TCP rather than on UDP? Wireshark Lab: HTTP (30 points) Wireshark Lab - HTTP: Answer question 1-15 in this lab. (2 points each) Refer to the solutions to Wireshark: Getting Started for the expected format of your answers.