Download Q1 - RMIT University

RMIT University
School of Computer Science
And Information Technology
COSC 1110
COSC 1111
COSC 2061
Foundations of Data Communications and
Networks
Assignment Guide
Semester 1, 2004
Warning regarding Plagiarism

Please remember that plagiarism and other forms of cheating are considered academic
offences, which in turn have academic penalties. The School of Computer Science &
Information Technology now routinely uses plagiarism detection software on electronically
submitted assignments.

Please read the information presented on the following web site:
https://inside.cs.rmit.edu.au/~jz/plagiarism/studentguide/
(use your yallara username/password to access this web site)

All other material that is not original must be fully credited. That is, any material that is
copied or derived from another source must be clearly identified as such and the original
author or source must be identified;

Sometimes students assist each other with an assignment, but end up working together too
closely, so that the students’ separate answers have significant parts in common; unless
answers were developed independently, they are regarded as plagiarized.

You must not provide nor show your answers, or part thereof, to anyone else but CS staff
(e.g. your marker). You are responsible for maintaining your work securely. This means not
leaving your handwritten papers unattended, not losing printouts or disks, and keeping your
file permissions set to prevent others from accessing your files and/or directory.

The minimum penalty for plagiarism is loss of marks for assignment. If this means that a
hurdle requirement is not met, then that could result in failure of the course.

Please be careful!!!
Introduction and Objectives of Assignment 2
 This assignment aims at giving a through understanding of the standard shortest path routing
algorithms, ARQ mechanisms, HDLC protocol, LANs, Network components, IP addressing
and link utilization mechanisms. This assignment two is worth 25% of your final score.
Due Dates and Assignment Submission
 This assignment two is to be completed by each student individually and independently.

The final version of your assignment #2 is to be submitted electronically using the turnin
facility on or before Monday the 24th May 2004 at 9:30 p.m. Assignment submissions will
be accepted only electronically.

You should submit the file with your name, and student number. The file name can be your
yallara login name.

We will accept late submissions of the assignment, which will be penalized as follows: For 1
to 5 days late, a penalty of 10% per normal working day. For assignments more than 5 days
late, 100% penalty.

Do NOT leave submitting your assignment until the last day; let alone the last hour or even
minute. You can resubmit many times up until the final cut-off time. If you leave submissions
until it is too late and find you have a problem (e.g. unable to connect) that is entirely your
own fault and no special consideration will be given.

Good Luck with your assignment 2!!!
Answer all questions
Q1.
(i)
Bob from RMIT sends few MP3 files electronically to John at Monash
University using Go-Back-N ARQ. The transmission link between RMIT and
Monash is mostly noisy. Bob finds Go-Back-N ARQ to be very inefficient for
a noisy link and decides to switch to Selective Repeat ARQ. Did Bob make
the right decision? If so, explain why Go-Back-N ARQ is very inefficient in a
noisy link, but Selective Repeat ARQ is found to be more efficient for the
same link.
Marks 10
(ii)
Consider the Stop-and Wait Protocol as described in the chapter. Suppose that
the protocol is modified so that each time a frame is found in error at either
the sender or receiver, the last transmitted frame is immediately resent.
a. Show that the protocol still operates correctly
b. Does the state transition diagram need to be modified to describe the new
operation?
c. What is the main effect of introducing the immediate-retransmission
feature?
Marks 2+2+2=6
(iii)
Consider the use of 1000-bit frames on a 1-Mbps satellite channel with a 270ms delay. What is the maximum link utilization for
a. Stop-and-Wait flow control
b. Continuous flow control with a window size of 7?
c. Continuous flow control with a window size of 127?
d. Continuous flow control with a window size of 255?
Marks 3+3+1+1=8
(iv)
a. How is bandwidth-delay product related to system efficiency?
b. Consider the various combinations of communications channels with bit
rates of 1 Mbps, 10 Mbps, 100 Mbps, and 1 Gbps over links that have
round-trip times of 10 msec, 1 msec, and 100 msec. Find the bandwidthdelay product for each of the 12 combinations of speed and distance.
Marks 2+4=6
(v)
Alice from RMIT sends data to Zhang at Monash University over a
transmission line that has a bandwidth of 2 Mbps and is mostly noise free. The
transmission system uses Stop-and-Wait ARQ, and 1 bit takes 10 ms to make
a round trip. The bandwidth-delay product is naturally 20,000 bits. If the
system data frames are 1000 bits in length, what is the utilization percentage
of the link? Why use of stop-and-wait for a high-bandwidth (or long-delay)
line wastes the capacity of the link? Does the utilization improve if the system
uses Go-Back-N ARQ with 15-frame sequence? How?
Marks 10
Q2.
(i)
Suppose a routing algorithm identifies paths that are “best” in the following
sense: (1) minimum number of hops, (2) minimum delay, or (3) maximum
available bandwidth. Identify the conditions under which the paths produced
by the different criteria are the same? Are different?
(ii)
Using Dijkstra’s routing algorithm, generate a least-cost route to all other
nodes for nodes 2 through 6 of the following figure:
Marks 8
Do the same using the Bellman-Ford algorithm.
Marks 8+8=16
(iii)
It was shown that flooding can be used to determine the minimum-hop route.
Can it be used to determine the minimum-delay route?
Marks 6
Q3.
(i)
What are the functions performed by a bridge? What is the difference between
a hub and layer 2 switch?
Marks 3
(ii)
Under heavy loads, how do the behavior of CSMA/CD and token ring differ?
Marks 2
(iii)
a. What is the fundamental difference between circuit switching and packet
switching?
b. A message is broken up into three pieces. Explain the transmission of the
packets using the datagram approach of packet switching.
c. Why does the internet use a connectionless network service.
Marks 5
(iv)
Diagrammatically represent a system of 3 LANs with 4 bridges. The bridges
(B1 to B4) connect the LANs as follows:
- B1 connects LAN1 and LAN2
- B2 connects LAN1 and LAN3
- B3 connects LAN2 and LAN3
- B4 connects LAN1 , LAN2, and LAN3
Marks 2
(v)
a. Identify the address class of the following IP addresses and also convert
them to their binary representations: 200.58.20.165; 128.167.23.20;
16.196.128.50; 50.156.10.10; 250.10.24.96
b. A host in an organization has an IP address 150.32.64.34 and a subnet
Mask 255.255.240.0. What is the address of this subnet? What is the range
of IP addresses that a host can have on this subnet?
Marks 4+5=9
(vi)
We currently use IPv4. What are the reasons we may need IPv6? What
strategies have been devised for the transition of IPv4 to Ipv6?
Marks 4
(vii)
Give an example of how multicasting saves network bandwidth.
Marks 5