Quick Links


 Module Organiser
 Ask a Question



 VB Sockets
 Java Sockets
 VB Code
 Java Code

 Pub Challenge
 OSI Model  
 Bits, bytes and frames
 IQ Test

Free Updates

Network Emulators
CNDS site

Back | Assign 1 | Assign 2  | Assign 3  | All  | [CNDS] 


Duration: 1 hour

Format comprises of two sections:

A: Multiple choice (based on material from Unit 1/2) based on:

Unit 1 (Introduction)
Unit 2 (Network Types)

B: Fixed format answers, based on:

Challenge 1: Network Topology.
Challenge 2: Network Modelling.
Research 1: Network Topology.
Research 2: Routes

Ask a question from Unit1/2

If you want to ask a question, please complete the following:



Matriculation number:



Alternatively if you have MSN Messenger you can ask a question at:



Questions asked

Hi Bill

I am hoping you can clear up a problem I am having with protocols relating to the levels of the OSI model. Your test has protocols such as telnet, ftp and smtp linked to the session layer but Cisco and http://webopedia.internet.com/quick_ref/OSI_Layers.asp have them all and more linked to the application layer (this is the way i originally understood it) could you clear up which one it is in case this stuff comes up in the test

Date/time: 11/1/02 10:26 AM

Answer: The model you quote is the Internet model, and lumps too many things together. Thus the OSI model is best, as it seperates the session from presentation, and so on, as it should be. Thus TELNET is an application program, but there is also a Telnet session protocol (RFC854 - which is quoted as an application layer protocol as related to the Internet model). The same is true with email, Microsoft Outlook is an email application, but SMTP (RFC788) and POP-3 (RFC1081) are a session layer protocols used to transfer email information. Another example is that Internet Explorer is a WWW Browser application, which uses HTTP (RFC1945 - Written by Berners-Lee, the creator of the WWW) as its session protocol, and a character transformation (such as US-ASCII) and HTML (RFC1866)for its presentation layer.

Hi Bill, Can we use a calculator in Tuesday's exam

Date/time: Fri 11/1/2002 3:48 PM

Answer: Yes. As long it is doesn't have a memory bank.


On the research topic how does fddi use timed tokens used to create priority

Date/time: Fri 11/1/2002 4:10 PM

Answer: Token ring allows for sharing over the network, but does not really implement priority, as a node must release the token once it has transmitted its data frame. FDDI improves this by allowing nodes to keep the token for a certain amount of time. For example one node could be setup to have the token for a maximum time of 0.5 seconds, while another can only have it for 0.05 seconds. Thus the first node would be able to transmit up to ten times as much data as the other, if it wants.


I don't understand question 6 of the FDDI research worksheet. I know that the base rate for FDDI is 51.84Mbps but don't know how to calculate the time when I don't know the distance. Am I missing something?
Additionally, are we expected th know this information before the exam or are we allowed to do the research on the internet during the exam.

A typical bit rate for FDDI is 100Mbps per ring. The time to transmit 1 bit will thus be 1/100e6 which is 1e-8s. The time to transmit say 56 bytes will be:

Time= 8 * 56 * 1e-8 s = 4.5µs

In the test you will not be allowed to open any Windows on the computer, thus you must remember the main principles involved in your research and challenges.

Hi Bill,

how many marks are assigned for each section (a + b) and can we use the windows calculator

In Section A there are 20 questions, each worth an equal rating. In Section B there are eight questions, each with an equal weighting. Yes, you can use the Windows calculator.

What is basic difference between interior and exterior routing protocols ? What is the answer for a question 2.8.17 (How does a router differ from a bridge ?) on the teaching pack ? A,B,C or D

An interior routing protocol is typically used within an organisation (typically grouped as an Autonomous System -AS), and an exterior routing protocol typically is used to route between these AS's. Example of an IRP are RIP (Routing Information Protocol) and IGRP (Interior Gateway Routing Protocol), and examples of ERP are EGP (Exterior Routing Protocol) and BGP (Border Gateway Protocol).

The best answer for the difference between a router and a bridge, is that a router routes with network address (such as the IP address), and the bridge routes with the physical address (such as the MAC address on an Ethernet network).

Hi Bill, RIP max. hop-count on your online /.../quiz_network_iq.htm (q 27) is marked correct for a max. hop-count of 14. Cisco say 16. We were told in NOS last week it is defaulted to 16 but can be set by admins. What\'s the correct answer?

The maximum that it can be set to is 16, which is infinity. Thus the maximum hop count is 15. Oops. I must have changed the IQ test by mistake, I'll set it back again.

hello Mr Buchanan

I would like to know if it exist last exam paper of the first exam.I haven\'t find it on the website.

For the test of tuesday, are there only questions by responding with choose the correct answer (like online test), or are there question by responding with explain? So,I would like to know if the online test that we do on tutorial are noted and if the note count for the final average.

The exam paper from last year is at:


Section A has multiple choice asnwers, and Section B has fixed answers. Section A has multiple choice asnwers, and Section B has fixed answers. The on-line tests that you have done do not count for anything.

Hi Bill You said that the questions were multiple choice and hand written for the exam on Tuesday. How many are multiple choice and how many are hand written

In Section A there are 20 questions, each worth an equal rating. In Section B there are eight questions, each with an equal weighting.

In the exam on tuesday will we have to answer all the fixed format questions or do you want us to do these questions online and submit them

You will get a printed exam paper, which you complete. We may also ask you to complete your answers on-line, but the paper copy provides the main system for answers.

Will there be any questions about the worksheets, like ping commands and ipconfig etc.

The module is continually assessed and everything that you do can be assessed in some way, this it is a good idea to revise your worksheets.

I have a hesitation about the encapsulation question answer. The two answers seem to be right but, encapsulation is better "adding additional information that the data can be viewed properly" or "wrapping the data in a particular protocol header"

The viewing of data only really occurs at the presentation layer, thus the best answer is wrapping the datab in a particular protocol header.

In the on line test the answer to the question "What is the name given to the retransmission delay after a collision" is Collision Timeout but in the notes page 32 note 2.7 it states that it is called "Backoff". Which is the correct term?

Good question. Any of the two answers would be acceptable, but the best is probably Collision Timeout.

Bill, When using RIP as the routing protocol, what is the maximum number of hops? In the notes it says 16 but I think you said 15 in Thursdays lecture?

The maximum that it can be set to is 16, which is infinity. Thus the maximum hop count is 15.

Hello Mr Buchanan I am writing to you to enquire about the research part of the test we are to take this Tuesday. My question is:

Will we be given a subject to do research on during the test, or will we be asked some of the questions we' ve already answered in the past researches.

That's a good idea, that we can maybe use in the future, but for this exam the material is only based on the research work that you have done for the weekly activities.

Hi Bill, Any chance of letting me know if there will be a lot of stuff based on binary\hex in the exam.

It's a good idea to understand the main concepts of decimal-to-binary and hexademical-to-binary conversion, and vice-verse, but I wouldn't make this the focus of your studies.

Hi Bill, Can we use a calculator in Tuesday's exam

Yes, as long as it is a Napier-approved one.

What was the correct answer to Challenge 1? How did you come to that answer?

To be answered.

Hi Bill,

I am a bit confused regarding error and flow control. On page 6 of the notes the data link layer deals with identification of errors and re-transmission of those data. On page 8 the transport layer appears to do the same thing. Could it be that the error hadling at the data-link layer pertains to data being passed between nodes on the same segment and the transport layer deals with errors passed to external networks networks


The data link layer is responsible for the point-to-point detection of errors and retransmssions. The method used for this varies greatly, from highly robust detection (such as Ethernet), to simple parity checks on the transmitted data (such as with RS-232). The data link layer also, typically, does not sequence data frames, thus there is thus no guarantee that when the data packets arrives, that they will be in the correct order, or if there are many missing. It is thus up to the transport layer, so some other high-level protocol to provide enhanced reliability.

Hi Bill,

I am confused with the answer you gave on the web about timed tokens on FDDI. 1. Cisco's handbook extract: "Token ring networks provide priority system... that permits certain user-designated, high-priority stations to use the network more frequently. Token Ring frames have two fields that control priority: the priority field and the reservation field. Only stations with a priority equal to or higher than the priority value contained in a token can seize that token... 2. For FDDI several websites describe an extra technique based on TTRT (target token rotation time) which also makes use of the priority bit of the token but no mention to timed tokens.

In a pure token ring network, there is no priority given to nodes, and all will have an equal share. In IBM Token Ring there is a facility in the token to grant priority, but this may not necessarily be properly implemented.

In FDDI the time that a station can hold onto a token is defined as the token holding time (or a timed token), where a station can transmit data frames until a given time-out on the token occurs.This holding time is defined as a system parameter.

For the test tomorrow I understand it will be divided into two

1. Multiple choice
2. Problem solving

I do not understand what problem solving means.Does it mean both the challenge and the Research?


MSN Message: Im just wondering why in your challenge doesnt data travel at the speed of light in fibre optic networks? Is that just for the purposes of the example ? Surely they are laser light signals so they always travel at the speed of light?

Well. Fibre cable is made out of plastic or glass. Light slows down when it enters a more dense material. Typically light will travel at only 1/3 of the speed of light along a glass fibre. It also bounces along the cable, so it doesn't take a straight path. In free space it will travel at the speed of light, but it is very quickly reduced in strength.

MSN: It will always be quite a variable number then ?

No. It should be well known for the cable being used. It is possible to calibrate equipment to determine it though, such as set up a 1000 m cable, and let the pulse bounce off the end, and measure the time taken.

Hi Bill, If we are required to use a value for pi in the exam to what level of precision should we use?

3.14 should be fine. But you might want to use 3.14159.