B227 Data Communications

Frequently Asked Questions (FAQs)

Table of Contents:

Are tutorial attendance compulsory for internal students?
I've read some parts of the textbook, and I don't understand any of it. What do I do?
In the lecture notes page, what is the difference between the links to Overheads and the links to Overheads with notes?
In the week 7 Tutorial on Basic Network Tools, the command "arp -a" is not producing what it is suppose to. Is there something wrong?
Are the ping and traceroute tools available in Windows?
Some lines in the traceroute output just have * in them instead of round-trip times. What do those lines mean?
In Assignment 2 Chapter 3 Q3, am I suppose to put bits in, or take bits out?
Are the answers for all questions in Assignment 2 in the textbook?
In the project description for internal students, what do you mean by "Personal evaluation of the project as a whole..."?
In the project, the budget doesn't allow me to implement what I want to implement. What do I do?
In the group project for internal students, how do we submit the group and individual parts?
Is any material covered in the tutorials going to come out in the exam?

Are tutorial attendance compulsory for internal students?

No. All tutorial attendances will be voluntary. The tutorials will consist of following doing practical exercises on the computers. The exercises themselves will not be assessed, BUT you must know them to complete parts of Assignment 2 and the Project. They will also help you understand the concepts presented in lectures. Make sure you keep up with the work.
I've read some parts of the textbook, and I don't understand any of it. What do I do?

First of all, don't panic. The textbook is not easy to read without guidance. The study strategy I suggest you take is:
1. Read the lecture overheads and notes. Try and understand what I put in the notes.
2. Consult your tutor, or me, if you want clarification on anything in the lecture notes.
3. Look at the Readings section in each Topic in the lecture notes page, and read the sections I've indicated. Most of them should already be summarised in the lecture notes.
The book will be invaluable to you once you have a basic understanding of the underlying concepts. At this stage, you should read about the details (and the book has A LOT of that), but not spend time memorising names and figures. Concentrate on why something is the way it is, and how it works.

Then why use this textbook, you ask? It is still the most best book covering the material I feel you should know, and giving it in a perspective I feel is best. Also, as I've said, it will be an invaluable reference once you have a basic understanding of Data Communications.

One day, I'm hoping Tanenbaum will write the same book in English. :-)

Again, let me stress, you will not make much head-way if you are a beginner to Data Communications, and you try to read the textbook on your own. It's a recipe for confusion! Read the lecture notes first.
In the lecture notes page, what is the difference between the links to Overheads and the links to Overheads with notes?

The Overheads with notes contains extra comments, descriptions, elaborations on the materials on the Overheads pages. The reason why I even have the Overheads pages is so that I can out them on before the lectures, and internal students can print them out and jot comments on them during the lecture. At the time of the lecture, I probably wouldn't have the Overheads with notes ready by the time lectures comes along.
In the week 7 Tutorial on Basic Network Tools, the command "arp -a" is not producing anything. Is there something wrong?

My wordings for the exercise sheet may be a bit misleading. ARP is suppose to tell you about machines which it receives packets from (I think the way I described it in the exercise sheet, it implies the output from ARP is information about your own machine - that is not so). So when you first start up the machine, you probably will not have any entries in the ARP table, and "arp -a" will not produce anything. You may occasionally get an entry to the main university gateway (gateway.murdoch.edu.au) because the boot-up process had some communication with the gateway, but that is not determinant.

Anothing issue is, ARP keeps its table in cache (memory) and occasionally flushes (clears) it. So you may get different results from ARP without doing anything.

It was probably my mistake to not mention this in the exercise sheet. What I would like you to do is to start a few communications using PING and TRACEROUTE. Then occasionally use the "arp -a" command and look at the ARP table. You will see address information about the machines which sent packets back to you.
Are the ping and traceroute tools available in Windows?

Yes, in an MS-DOS prompt. The name of the programs are "ping" and "tracert". Typing "ping" and "tracert" without any options will list the options.
Some lines in the traceroute output just have * in them instead of round-trip times. What do those lines mean?

The traceroute command sends out packets to all the intermediate routers in a path, and expects reply packets. It also starts a timer for each of those packets sent out. If the reply doesn't arrive before the timer times out, it will print a * in place of the round-trip time. The two possible reasons for this happening is if the packets got lost, or the traffic is so heavy it takes too long for the reply to come back.

For the sake of the Assignment 2 Q1 (for INTERNAL STUDENTS only), if you have some theory about why the lines with * are appearing, then go ahead and put them into the results.
In Assignment 2 Chapter 3 Q3, am I suppose to put bits in, or take bits out?

Put bits in - what the question is asking is "If you bit-stuff the string 0111101111101111110, what do you get?"

This should be obvious if you understand bit-stuffing and the format of the the bit-stuffed strings. The string cannot possibly be already stuffed. I do agree the question is not well-phrased though.
Are the answers for all questions in Assignment 2 in the textbook?

No. Some of the questions have direct answers, but not all. Unlike Assignment 1, which is a read-and-summarise assignment, all the questions in Assignment 2 requires thinking a bit about the material you've read.

Don't worry, the exam questions will not be anywhere near as tough as the assignment questions.
In the project description for internal students, what do you mean by "Personal evaluation of the project as a whole..."?

This is a component to demonstrate your ability to self evaluate your and your team's achievements. No project is ever perfect. This is your chance to report on what went wrong, what were the major problems, what you would do differently to do better, etc. If you do say that everything went perfectly, then I would expect a perfect project submission.
In the project, the budget doesn't allow me to implement what I want to implement. What do I do?

Welcome to network design! :-)

Your job is to work within the budget and satisfy the requirements AS FAR AS POSSIBLE. You may do anything you like and make any assumptions, as long as it doesn't violate what the project description states. Just list the assumptions in your submission.

Don't make blatantly stupid assumptions, like the manager just won the lottery and decided to buy everyone brand new machines with her/his own money!
In the group project for internal students, how do we submit the group and individual parts?

There are two cover sheets on the assignments page - one for the group submission and one for the individual component. Your group should submit ONLY ONE group submission with one group cover sheet with 3 names on it. EACH group member should also submit separate individual components with an individual cover sheet.
Is any material covered in the tutorials going to come out in the exam?

No, only the material in the textbook as required in the "Required Readings" of every topic. See the readings section at the end of ever topic in the lectures page.

H.L. Hiew
Unit Coordinator