What is an OSI model?
 
      OSI stands for Open System Interconnect. It was developed by the International Organization for Standardization in 1974. The OSI model consists of seven layers with each layer having a different function of processing.
The seven layers of OSI Reference model are as follows:

• Application layer
• Presentation layer
• Session layer
• Transport layer
• Network layer
• Data link layer
• Physical layer

OSI Model

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The Open System Interconnection model defines implementations for networking framework protocols in seven layers. Starting from the application layer in one station, the control is circulated from one layer to the other over the channel to the next station and back up the hierarchy.

Application layer

The application layer is the seventh or topmost layer of the OSI Model. The Application Layer is responsible for providing end-user services, such as file transfers, electronic messaging, e-mail, virtual terminal access, and network management. This is the layer with which the user interacts with the application. This interface may be command-line-based or GUI-based. Cisco routers and switches have a command-line interface, while a web browser uses a graphical interface.The application layer refers to applications that are network-aware. There are thousands of computer applications, but not all of these can transmit information across a network Examples of application layer programs are telnet, FTP, web browsers, and e-mail.



Presentation layer
The Presentation Layer establishes context between Application Layer entities, in which the higher-layer entities may use different syntax and semantics if the presentation service provides a mapping between them. If a mapping is available, presentation service data units are encapsulated into session protocol data units, and passed down the stack.


Session layer
 The session layer is the fifth layer of the OSI model that controls the connections between computers. Its responsibility is to establish, manage and terminate the connections between the client and remote applications. Session layer provides full duples, half duplex and simplex operaions of communication.

There are four main phases or sequences of hosting a website, which are discussed below:

• Simple internet presence

           This is the most common and most basic type of website that is simplest to set up and least expensive as well. This type of website is a medium of direct communication of an website owner to the clients. It contains general information about the business firm, its objectives, missions, news, press releases, products and views, services, contact information etc. It may contain annual reports and specialized news bulletins, as well as a dedicated area for visitor feedback.

• Basic E-commerce or E-business website

               This category of website is somewhat complex version of the simple internet presence website, complex to mean that it consists of much more information compared to the simple internet presence websites. It consists of a number of substantial enrichment features that provide extra functionality to the website. The extra features may consist of an online store of various goods and services with secure ordering capabilities, integrated online call centers, FAQs and fact sheets, etc.


 Advanced E-commerce or E-business website 

 
               Advanced websites consist of increased functionality such as web based software and core applications to dynamic IP based systems and applications. Off-the-shelf and custom software applications can be integrated with enterprise websites to enhance various processes in a number of areas such as automated processes, general business applications, data management functions and automated software, private IP-based networks, etc.

• Fully Integrated E-business web presence

           At this fourth stage of development, the firm or enterprise has become a fully integrated E-business with intranets, extra-nets and discrete enterprise system working together. The back-office and front-office functions work together as an integrated system for the ease of ordering, asset and inventories management, and knowledge management throughout the system. In this model, the institution has become a true E-business.