Correction for NS2 Book: ARQ Codes

This is the correction for the following book:

T. Issaraiyakul and E. Hossain, "Introduction to Network Simulator
NS2", Springer 2008.
http://www.springer.com/engineering/signals/book/978-0-387-71759-3


If you are trying to run the ARQ codes in chapter 14, it will not work. You need to add the following code into your arq.cc file:

static class ARQTxClass: public TclClass {
public:
ARQTxClass() : TclClass("ARQTx") {}
TclObject* create(int, const char*const*) {
return (new ARQTx);
}
} class_arq_tx;

You might also find the following slide useful:
http://www.ece.ubc.ca/~teerawat/NS2.htm

Best,
Teerawat

"Can I use NS2" v.s. "Do I need NS2"

Yes, NS2 is a very powerful network simulation tools. A lot of people wants to use it (some without knowing whether they really need NS2). A common question is that "Can I use NS2 for my work?" Unfortunately, no one knows the answer more than yourself. In fact, it is more appropriate to rephrase the question as "Do you really need NS2?" A tough one, eh?

So, here are some question which can help you determine whether you need NS2.

- You don't want to use NS2 if your work is self-contained. If your work does not need any interaction with many other component (e.g., determine bit error rate for a particular modulation), it would be easier to write codes in a basic programming language (e.g., C++).
- You want to use NS2 if you work is so connected to other components and you don't want to re-create those component. NS2 has a whole lot of modules that you can re-use. Those modules are written and proved by others. They are quite robust and ready to use. If for example you want to study TCP performance for your new modulation scheme, you might consider writing your own modulation module and use TCP module available in NS2.

Come back to our original question: "Can I use NS2 for my work?" Well, the answer is always YES! NS2 is just a combination of C++ and Tcl. If your work can be programmed by using C++, Tcl, or both. You can use and integrate your work into NS2. But, again, if you don't need to, don't bother using NS2. After all, use NS2 to make your life easier. Do not enslave yourself by using NS2 :)

For more information about language structure (C++-Tcl) in NS2, please look at chapter 3 in the following book:

T. Issaraiyakul and E. Hossain, "Introduction to Network Simulator
NS2", Springer 2008.

Here is the link:
http://www.springer.com/engineering/signals/book/978-0-387-71759-3

You might also find the following slide useful:
http://www.ece.ubc.ca/~teerawat/NS2.htm

Best,
Teerawat

Cryptographic with Asymmetric Keys: Public Key and Private Key

Asymmetric cryptography uses one key to encrypt a message and another key to decrypt the encrypted message. One of the two keys is called a public key. Another is called a private key. As implied by their names, a public key is usually broadcast as general information, while a private key is kept confidential. A private key has no relation to a public key. There is no way (or with little possibility) of inferring a private key from the knowledge of public key.

A -->|Message|-->B

Suppose we would like to protect a message from A to B from being eavesdropped (e.g., in a website with https:://).

The process proceeds as follows:

1. B broadcasts its public key.
2. A recognizes the public key of B.
3. A encrypts the message using the pubic key of B, and sends the encrypted message to B.
4. B decrypts the encrypted message using its private key.

Since there is no way of inferring the private key from the public key, no one benefits from knowing B's public key and the messaged remains gibberish to everybody who does not know the private key of B.

Clearly, the public key is a powerful concept which allows end-to-end encryption without having to share the key apriori.

Linux initialization files: .bash_profile and .bashrc

As a Linux or Cygwin (Linux emulation for Windows) new, would you wonder what really happen when you execute the shell (e.g., double click on the Cygwin icon)? In the old day, Windows always invokes a file called "autoexec.bat". This file contains a bunch of thing the the window will do at the boot-up such as setting path or invoke other programs (e.g., anti-virus).

In your home directory, there are two files, ".bash_profile" and ".bashrc", which are the initialization file in the Linux. When you open a shell, they are automatically executed as a shell initialization.The path setting is contained in these files.

The difference? According to [Josh Staiger],

- ".bash_profile" is invoked for a log-in session. Log-in? Yeah, log-in. It means anything that you usually need to provide user name and password such as log-in physically at the boot-up or using ssh

- ".bashrc" is invoked for a non-log-in session. For example, when you have already log-in to a graphical environment such as KDE. All you have to do is to click on a terminal icon and you don't have to provide username/password to open a shell.

In fact, you can see in the file ".bash_profile" the following

if [ -f ~/.bashrc ]; then
source ~/.bashrc
fi


which basically invokes ".bashrc" if it exists.

For the Cygwin environment, you can add your own initialization in either ".bashrc" or ".bash_profile". Wanna try? Add the following lines into the files and restart the shell.

- Add to ".bashrc"


echo Add2.bashrc


- Add to ".bash_profile"

echo Add2.bash_profile

PATH=${PATH}:
export =


ENJOY...

Is Low-level format sufficient to protect your sensitive (private) data?

Unfortunately, NO!! If you have private data that you don't want others to see, and you think that you can get away with a low-level formatting before somebody gets their hands on your hard drive, THINK AGAIN.

Well, a hard drive is just an electrical device. It records data (0 or 1) in a form of electric current. Unfortunately, low-level format simply puts 0 on all the sectors of your hard drive. This pattern of formatting make it easier for a guesser to recover your sensitive data.

How? Think of a tape recording. Suppose you have a conversation that you don't want people to know about. So you re-record with noise (i.e., press recording buttons and say nothing). When you play the tape, you will hear nothing and you think your data is now safe. Unfortunately, somebody may still recover your private conversation.

Here is how forensic recovery works. Well, tape now contain noise over your conversation. The capability of regular human ears would probably not be able to differentiate between the noise and the background conversation. With the current technology, your conversation can be recover without the ears of Clark Kent :) This is as simple as amplifying the sound in the tape and filtering out the noise. This simple signal processing technique can recover your private conversation.

What about the hard drive. Well, when you replace every sector with zero (low-level format). The electric voltage in the sector is not exactly 0 Volts. There is a little electric trace that can tell what was there before the low-level format. Knowing that all the sectors in a hard drive was replace with zero values, it is easy for a forensic team to recover your information. It is hard, but not impossible.

So how do you prevent your private information. Well, the easiest way is to replace data in all the sectors with pseudo-random binary data. Not knowing what was in the hard drive, the forensic team will have a hard time recovering your data. Typically, two runs of pseudo-random overwrite would be sufficient to protect your information.

Source: Security Now: EPS 150

Realtime Transit Map

Talking about transit map... What a boring topic... Not really, if we see the realtime transit map in Helsinki, Finland.


View Larger Map


We can see where the buses is in the map REALTIME!! The map allows you to zoom-in zoom-out move around like a Google Maps. If you can't see buses moving, checkout time in Helsinki. People may be sleeping :)

In a cold place like that, you can stay in the office and start leaving the office few minutes before the bus arrive at the bus stops. Pretty neat, eh?

Upcodes: Picture-Based Identifiers

UpCode is another picture-based identifier, which can be used for anything. It can be used for various purposes:

• Advertisement in newspaper
  
• Bus stop information
• Bus tickets
  
• Video clip identifier
• Business cards

The neat things about upcodes is that you can read an upcode with your cellphone. Just take a picture of the upcode and send it over to the server, and you will get the info. about the upcode.

Cost? Well, it depends on the business model. In Helsinki, Finland, the transit let their customers use the upcodes for free!! Example use is to find out when the bus will arrive at a bus stop or to use an upcode as a bus ticket.

Wanna know more about upcodes, visit http://www.upc.fi/en/upcode/