July 24, 2012

QR Code : Explained

QR Code - A common term that is seen in the media that reads "Scan your smartphone here to get more details". Its a modified version of Bar-Code that has some added features of readability even in damaged code. QR Code is the one that comes with auto error correction. So what is QR Code?

QR Code - Quick Response Code is a combination of Black and White squares as it is below:


The most beauty part of it is that any one can make this code and any one can generate them for free. Of course the unique one. Once the QR Code is generated or created, one can modify its colour, graphics, or even one can mess it up! One needs not to be a great hacker to crack the code, just knowing the basics can make it all.

QR Code is a 2 dimensional code that is categorized in matrix code. 
The features of QR Code are:
  1. High speed in reading the code.
  2. Error correction.
  3. High capacity.
Since the QR Code has been created, it is available in two models- Original and Extended model. Extended model is the one in use now-a-days. Depending upon the number of characters used, the size of the QR Code changes. More the characters, big is the size. Though it can hold any number of characters, QR Code scanner (smartphone!) finds difficult to scan the code. 


Versions and Character encoding:
Depending upon the size of the QR Code, the version number changes. There are around 40 versions available starting from 21*21 grid pattern for version 1 to 177*177 grid pattern for version 40. QR Code can hold:
  • Numeric characters(0-9) - 10 Characters
  • Alpha-Numeric characters(0-9 A-Z special symbols) - 45 Characters
  • 8-bit data
  • Multi Byte data

Know QR Code:

  • Three large squares marked RED are position markers. These tells the scanner where the edge is.
  • A single small square in RED is an alignment  marker that tells the scanner that the codes are lined up properly. Their number increase when the size of the grid increases as here.
  • RED stripes that runs over the alternative white and black squares is a timing pattern, defines the position of number of rows and columns.
  • GREEN tells the format of the QR Code as it is a website or text message or a phone number.
  • BLUE area describes the version number used in the QR Code. (It is already discussed few lines before)
Here is a pictorial representation. These areas are the sensitive ones and other areas can be changed depending upon your data.

Error Correcting:
An added feature of QR Code is error correcting. QR Code defines 4 levels of error correction in case the white and black squares are misread. 
  • Level L: Up to 7% of the error can be corrected.
  • Level M: Up to 15% of the error can be corrected.
  • Level Q: Up to 25% of the error can be corrected.
  • Level H: Up to 30% of the error can be corrected.
Because of this error correction, you can create an error for sure as it is here.

You can do even like this as it is Here. It is still readable until you don't touch the sensitive areas as it is described above.

Now you can create your own QR Code for your Products or Website or E-Mail or Phone Number... Or generate online here for free. Google can fetch you some more online QR Code generators.


July 19, 2012

Domain Types

There are many types of domain in the internet world. Here I do not mean it as .com or .co.in or something like that. I come to say about Parked Domains, Sub-Domains, Add-on Domains and Redirects.

Parked Domain
Suppose, say you have two domain names like mydomain.com and my-domain.com. If you want the users to point to the same website from mydomain.com and my-domain.com, then this is the right choice for you, which means that when the users type mydomain.com or my-domain.com, DNS (Domain Name Server) will direct the user to the same website.

Try it: Everyone knows Google website. You just type www.google.com to access that website. Have you just tried www.gooogle.com or www.ggoogle.com? You may wonder that it all directs you to same page!
This is the use of Parked Domain.



Sub-Domain
An online company wants to have a forum website for its main website. Though the forum is needed for it, they do not buy another website for forum, instead they use the existing website as the link to it. In other words, sub-domain utilizes the existing domain name. Consider mycompany.com is a company's domain name, if it wants to add a forum page to its website and to be shown as a unique one, it just creates a sub-domain as: forum.mycompany.com. Its just the concept of replacing www with your own words.

Know it: forum.mycompany.com is a sub-domain and it also can be called from www.mycompany.com/forum
This is how the sub-domain can be used as a unique domain. Sub-domains are usually free and is most preferred in order not to change a domain.



Add-On Domain
It is like having two seperate domain names with different contents but with the same hosting account, which means your content is split in public_HTML folder inside your hosting account itself. Main account and Add-on account uses same bandwidth of the hosting account but different nameserver. Here the advantage is that add-on domain can be accessed either separately or can be accessed from you main account as :

addondomain.com
maindomain.com/addondomain
addondomain.maindomain.com



Redirects
This is different from those previously discussed domain types. Those domain names are dependent on your webhosting plan. But Redirect is the concept that you point out a website either to your blog or a social networking profile or even a website hosted in a different web server. Some redirects allow you to point out your IP address similar to the DNS address. The Redirecting server do not host your website or its contents rather it stores the URL that is to be redirected when the redirecting URL is entered in the address bar. Some services even allows masking of the real redirecting URL and displays their URL.

July 15, 2012

CDPD vs CMDA vs GSM vs GPRS vs EDGE

CDPD :


Cellular Digital Packet Data
  • Packet-based network.
  • Optimal bandwidth of 19.2 Kbps.
  • Run in the same spectrum as the AMPS networks.

CDMA :

Code Division Multiple Access
  • Either packet based or circuit based.
  • CDMA1 :  Uses circuit switch data, that runs at 14.4 Kbps, and acts as a dial-up connection.
  • CDMA2000 : packet based, and has a maximum of 144 Kbps, and delivers 50-120kbps in real world usage.
GSM :

Global System Mobile Communication
  • Circuit-based network.
  • The user must make a dial-up connection to access the network.
  • Optimal bandwidth of 14.4 Kbps.
  • Provides voice service through digital network.
  • SIM card (Subscriber Identity Module card) stores phone number, connection information, and may store an address book. 
  • This allows a user to switch devices without needing to contact the service provider.
GPRS :

General Packet Radio Service
  • Packet-based wireless communication service.
  • Extends the GSM network that allows for advanced data services.
  • Data rates from 56 up to 114 Kbps and continuous connection to the Internet for mobile phone and computer users, but delivers in the 30-50 Kbps in real world usage.
  • Advantage over GSM is that one can use the device as the modem or as an Web-Browser.
EDGE :

Enhanced Data for Global Evolution
  • An extension to the GSM / GPRS networks.
  • 3 times faster than GPRS.
  • Download speed extends about 300 Kpbs.

July 8, 2012

Internet blackout Monday: Check if your PC is infected

Today is Internet Blackout Monday. So check your computer whether it is affected or not here:
http://www.dns-ok.us/

If you get green pic as DNS Resolution, you are not affected. If your computer is infected with DNS changer malware youwill have seen a red background.

If you see red background, here's the fix:
http://www.dcwg.org/fix/



dns_changer_check.jpg