Wednesday, April 29, 2015

Tackling the CIE Exam Papers

The following material is original to the authors and the University of Cambridge Local
Examinations Syndicate are not responsible for the advice given. Please note that the information
that follows is not necessarily true for all questions. There will always be exceptions to general
rules and so these are intended only as a loose guide.
 
General tips
In many cases, you can find clues about the answer within the question itself. The main ‘clues’ are:
• the number of marks given for the question
• the key instruction words e.g. Name, Describe, Compare, Evaluate ...
• instruction/question text written in bold typeface.

The number of marks
Th e number of marks awarded for a question is given in square brackets [ ] after each question or
sub part of a question. Typically (though not always), the number of marks gives an indication of
how many different points you need to make. For example:

Explain what is meant array?                                                                            [2]

There are potentially 5 or 6 different points you could make to answer this question successfully.
However, as it is only worth 2 marks, the examiner is most likely only looking for any 2 correct
comments. You could spend 20 minutes writing 6 accurate comments but you would still only
score 2 marks because this is the maximum allowance for the question.

You won’t lose marks for writing extra answers, but you could waste time writing points that won’t
score you any more marks. Also, the examiner might decide to only look at the first 2 points and
ignore the rest. So, make sure you always put the answers you are certain are correct first before
any additional answers.

Th e number of marks indicates the likely number of separate points you need to make and it is also
a good indicator of how much time you should spend on that particular question. For example, it
is more sensible to spend much longer writing the answer to a question worth 5 marks than one
worth 1 mark. BUT this is not always the case. For some questions the number of marks does not
indicate how many comments you need to make. So, you should always take the time to think
about the questions and your answer before committing pen to paper.

Key instruction words
Th e examination questions will oft en have a single word that tells you how much detail is required
for each answer. Typically, the following is true:

• State, Name, List means that all you have to do is give the name of what is being asked for.
• Describe, Explain means you should say how something works (this will depend on the actual question, it
   might not always be how but it infers more detail than simply listing a name).
• Compare means you should say how both things work and sometimes what are the differences between
   them.
• Evaluate means you should say how well or poorly the object/method/application etc. works, or how
   suitable something is for a given scenario.
• Justify means you should say why the object/method/application etc. has been chosen.

Think about what each of these words is asking for in the question. This can really help you write a
good answer.

Instruction text written in bold or capitals
Th is applies to general text within the instruction/question as well as the key instruction words
mentioned above. When certain text is given in bold or sometimes CAPITALS it is meant to draw
your attention to it and emphasise its meaning.

Often a question will ask you to give ‘two examples of ’ where the word ‘two’ is written in bold
typeface. Th is means that you have to supply at least two examples in order to get the marks even
if the answer is only worth 1 mark! In other words, it is a clue to the minimum number of different
points you need to make regardless of the number of marks. Similarly, if the question included the
instruction to ‘Evaluate’ it means that you have to do more than simply state the name of a term.
You have to also discuss its advantages and disadvantages, for example. In such cases, you are being
given a direct and clear instruction and you must follow it in order to get the marks.

Examination technique
An hour of revision the night before the examination is a good idea. It is not a good idea to cram
in as much revision as possible at the last minute by spending hours revising the night before; or to
stay up into the early hours of the next morning.

What you really need to do is:

• get a good night’s sleep and relax in order to be in a positive frame of mind
• make sure you have the correct equipment (remember to take spare pens)
• when you get to the examination room:
– arrange your equipment on the desk and relax
– before you write anything, quickly read through all the questions on the examination paper,
   the last question is not always the hardest
– start by answering a couple of the easier questions to boost your confidence, then tackle the
   more diffi cult questions
– an alternative would be to answer the questions in increasing level of difficulty so that you
   leave the more difficult questions until the end
– remember to keep an eye on the time, don’t spend too long on any one question, even if you
   know everything there is to know on that particular topic. Th e question paper will usually
   tell you how many marks there are for each question and so you can use this to work out
   how much time to spend on each question
– in cases where you have to write in the answer, make sure that you answer every question
   even if you are having to guess. You cannot score marks if you don’t give an answer, but an
   educated guess could end up scoring you marks.

   Make sure you take whatever approach works for you. We are all different and work in different ways.
   Above all, READ THE QUESTION THOROUGHLY.



Wednesday, April 22, 2015

TCP/IP and Mac Address

MAC address:

A media access control address (MAC address) is a unique identifier assigned to network interfaces for communications on the physical network segment. MAC addresses are used as a network address for most IEEE 802 network technologies, including Ethernet and WiFi. Logically, MAC addresses are used in the media access control protocol sublayer..

MAC addresses are most often assigned by the manufacturer of a network interface controller (NIC) and are stored in its hardware, such as the card's read-only memory or some other firmware mechanism. If assigned by the manufacturer, a MAC address usually encodes the manufacturer's registered identification number. It may also be known as an Ethernet hardware address (EHA), hardware address or physical address. This can be contrasted to a programmed address, where the host device issues commands to the NIC to use an arbitrary address.


What is TCP/IP?

TCP/IP stands for Transmission Control Protocol / Internet Protocol. It defines how electronic devices (like computers) should be connected over the Internet, and how data should be transmitted between them.
TCP - Transmission Control Protocol
TCP is responsible for breaking data down into small packets before they can be sent over a network, and for assembling the packets again when they arrive.
IP - Internet Protocol
IP takes care of the communication between computers. It is responsible for addressing, sending and receiving the data packets over the Internet.

TCP/IP Protocols For the Web

Web browsers and servers use TCP/IP protocols to connect to the Internet. Common TCP/IP protocols are:
HTTP - Hyper Text Transfer Protocol
HTTP takes care of the communication between a web server and a web browser. HTTP is used for sending requests from a web client (a browser) to a web server, returning web content (web pages) from the server back to the client.
HTTPS - Secure HTTP
HTTPS takes care of secure communication between a web server and a web browser. HTTPS typically handles credit card transactions and other sensitive data.
FTP - File Transfer Protocol
FTP takes care of transmission of files between computers.

What is SSL?

What is SSL?

SSL stands for Secure Sockets Layer and is one security protocol that is used on the Internet. This is the technology that will show a “lock icon” and/or a green address bar on the browser to let people know that they’re visiting a website that is secured with SSL / TLS. (Note: TLS refers to Transport Layer Security, which is a broad security protocol that SSL fits into.)


Simply, SSL is a way to encrypt data that is sent from a web browser (like Internet Explorer, Firefox, or Chrome) to the web server. While it was primarily used in the past to protect sensitive information like credit card numbers and other data, these days it’s becoming used on a wider basis.

Without encryption, any information sent from the web browser to the web server can fall prey to a man-in-the-middle attack – which refers to bad guys grabbing the data after it leaves the browser and before it reaches the server. By encrypting the data going from a browser to a server, it’s possible to make man-in-the-middle attacks more difficult to pull off successfully.

Understanding Public Key Cryptography

To understand how SSL protects sensitive data, you need to know a thing or two about public key cryptography. While this deals with a lot of very complex math, we’re going to skip over a lot of the technical details in this guide and give you just the basic information you need to know in order to understand how SSL works.
Basically, to use an SSL connection, a public key and a private key are used. The web browser uses the public key to encrypt the data and the server uses the private key to decode the information. Instead of encrypting and decrypting keys every time a connection is made – which would take a lot of processing power – a symmetric key is created after the initial communication between the browser and server.

Establishing an SSL Connection

Next, I'm going to give a very basic outline of the process of establishing an SSL connection.
  1. Browser requests a HTTPS webpage
  2. Web Server sends public key and certificate
  3. Browser examines the SSL Certificate
  4. Browser creates a symmetric key and sends it to server
  5. Web server decrypts symmetric key with its private key
  6. Web server sends browser the page with symmetric key
  7. Browser decrypts the data and displays page
What’s amazing is that all that happens very quickly – without most people even noticing it’s going on under the hood.

Computer Systems (FAST TRACK)

1     Data representation   1.1    Number systems   How and why computers use binary to represent all forms of data? •     Any form ...