(Networking Basics): TCP, UDP, TCP/IP & OSI models

 

The Transmission Control Protocol/Internet Protocol (TCP/IP) suite was created by the U.S. Department of Defense (DoD) to ensure that communications could survive any conditions and that data integrity wouldn't be compromised under malicious attacks.

 

The Open Systems Interconnection Basic Reference Model (OSI Model) is an abstract description for network protocol design, developed as an effort to standardize networking.

 

Comparing TCP/IP and the OSI Models

 

The TCP/IP model is basically a shorter version of the OSI model. It consists of four instead of seven layers. Despite their architectural differences, both models have interchangeable transport and network layers and their operation is based upon packet-switched technology. The diagram below indicates the differences between the two models:

 

 

 

 

 

 

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  Application Layer: The Application layer deals with representation, encoding and dialog control issues. All these issues are combined together and form a single layer in the TCP/IP model whereas three distinctive layers are defined in the OSI model.
  

  
   

  
   

  
   

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  Host-to-Host: Host-to-Host protocol in the TCP/IP model provides more or less the same services with its equivalent Transport protocol in the OSI model. Its responsibilities include application data segmentation, transmission reliability, flow and error control.
  

  
   

  
   

  
   

Internet: Again Internet layer in TCP/IP model provides the same services as the OSIs Network layer. Their purpose is to route packets to their destination independent of the path taken.

ASCII Character Code List

Introduction to ASCII

ASCII stands for American Standard Code for Information Interchange. Computers can only understand numbers, so an ASCII code is the numerical representation of a character like 'c' or '#' or an action of some sort. Here are some sample ASCII codes and the characters they represent:
033 -- !

034 -- "

035 -- #

036 -- $

So for example the code '035' will give you the character: #

Why use ASCII codes

Knowing ASCII codes allows you to insert a character that is not found on your keyboard.
Examples would include: ™ ¾ ®

How to insert ASCII codes:

Place your mouse cursor where you want to insert the special ASCII character in your document:

1. Hold down the "ALT" key.
2. Type the ASCII number code.
3. Let go of the"ALT" key.

The character will appear on your screen at that location. Knowing ASCII codes is not only useful in web design, these codes will work in just about any program including software like MS Word and Excel and even simple programs like notepad.

If you happen to have a copy of MS Word, you can get to a list of ASCII character easily by selecting: Insert -> symbol. You have all your ASCII characters there but be careful, you will also find a bunch of characters that work in Word but not in your web pages.
Dreamweaver MX also has a 'Character' tab at the top of the window with many of these codes for you you to use.

The ACSII codes and HTML Entity Names

Notes

The HTML equivalent to the ASCII code is simply: An ampersand and hash before the ASCII number and semicolon following the ASCII number. So for example the ASCII code for $ (dollar sign) is the number 36, so the the HTML code for this is:
$

ASCII and HTML code table
Please note than when using the ASCII codes you need to always start with the number 0 (zero) then the code. So to get $ you need to type in 036 and not just 36.

UNICODE

What is Unicode?

Unicode provides a unique number for every character,no matter what the platform,no matter what the program,no matter what the language.

Fundamentally, computers just deal with numbers. They store letters and other characters by assigning a number for each one. Before Unicode was invented, there were hundreds of different encoding systems for assigning these numbers. No single encoding could contain enough characters: for example, the European Union alone requires several different encodings to cover all its languages. Even for a single language like English no single encoding was adequate for all the letters, punctuation, and technical symbols in common use.

These encoding systems also conflict with one another. That is, two encodings can use the same number for two different characters, or use different numbers for the same character. Any given computer (especially servers) needs to support many different encodings; yet whenever data is passed between different encodings or platforms, that data always runs the risk of corruption.

Unicode is changing all that!

Unicode provides a unique number for every character, no matter what the platform, no matter what the program, no matter what the language. The Unicode Standard has been adopted by such industry leaders as Apple, HP, IBM, JustSystems, Microsoft, Oracle, SAP, Sun, Sybase, Unisys and many others. Unicode is required by modern standards such as XML, Java, ECMAScript (JavaScript), LDAP, CORBA 3.0, WML, etc., and is the official way to implement ISO/IEC 10646. It is supported in many operating systems, all modern browsers, and many other products. The emergence of the Unicode Standard, and the availability of tools supporting it, are among the most significant recent global software technology trends.

Incorporating Unicode into client-server or multi-tiered applications and websites offers significant cost savings over the use of legacy character sets. Unicode enables a single software product or a single website to be targeted across multiple platforms, languages and countries without re-engineering. It allows data to be transported through many different systems without corruption.

About the Unicode Consortium

The Unicode Consortium is a non-profit organization founded to develop, extend and promote use of the Unicode Standard, which specifies the representation of text in modern software products and standards. The membership of the consortium represents a broad spectrum of corporations and organizations in the computer and information processing industry. The consortium is supported financially solely through membership dues. Membership in the Unicode Consortium is open to organizations and individuals anywhere in the world who support the Unicode Standard and wish to assist in its extension and implementation.

Unicode in use
1. Operating systems

2. Input methods
3. E-mail
4. Web
5. Fonts
6. New lines