Open Systems Interconnection (OSI) is a standard description for transmitting messages between any two points in a telecommunication network. The purpose of the OSI is to guide product implementors and ensure the product will work consistently with other products. OSI consist of seven layer that were The application layer, The presentation layer, The session layer, The transport layer, The network layer, the data-link layer and lastly The physical layer. Each layer having difference special and related functions. These layers are separated into two group. the upper four layer are used whenever a message passes from or to a user. The lower three layers are used whenever the message passes through the host computer. The seven layers are:
Layer 7: The application layer
This layer is which the comunication partners are identified, quality of service is identified, user authentication and privacy is considered and any constraints on data syntax are identified.
Layer 6: The presentation layer
This layer is part of an operating system that converting outgoing and incoming data from one presentation format to another. This layer are also name as syntax layer.
Layer 5: The session layer
This layer sets up, coordinates, and terminates conversations, exchanges, and dialogs between the application at each end. It deals with session and connection coordination.
Layer 4: The transport layer
This layer will ensure the complete data transfer. It manage the end to end control and error checking.
Layer 3: The network layer
This layer handles the routing and forwarding of data. It make sure the data is send to the right destination on the outgoing transmission and incoming transmission at the packet level.
Layer 2: The data-link layer
This layer provides synchronization for the physical level and does bit-stuffing for strings of 1's in the excess of 5. It furnishes transmission protocol knowledge and management.
Layer 1: The physical layer
This layer conveys the bit stream through the network at the electrical and mechanical level. It provides the hardware means of sending and receiving data on a carrier.
Server-side code and Client-side code
In web applications contain the client and server. The client is like the web browser. The server is a web application server at a remote location that will process web requests and send pages to the client. There are several server-site technologies that can be used when developing web applications. Server-side processing is used to interact with permanent storage like databases or files. The server will render pages is first requested and when pages are posted back to the server. Server-side code required a long time to process unlike the Client-side code. Client-side code also having more interactive application and less overhead on the web server. Client side code is ideal for when the element of the page to be changed without contact the database. Client-side code form a validation alerts but Server-side code validating data prior to saving. moreover, Client-side code calculations based on page values but Server-side code filtering data by permissions. In Client-site code the layout positioning can be change but in server-site code must be deleting data or remove. Client-site code set values to input areas and server-site code working with sensitive data.
Application server and web services
Web services are services with standard interfaces that just expose a behavior. Web applications are full blown browser-based applications that also include an interface. Web services are granular. Web application are complete holistic functions that are bound into a single application. A web application is an application that is accessed through a web browser running on client's machine whereas a web service is a system of software that allow different machines to interact with each other through a network. Web server do not necessarily have a user interface, while a web application is a complte application with a GUI. Web services can be used to communicate or transfer data between web application running on different platforms.
The web application example is Google Documents, Meebo and Slide Rocket.
The Web Services example is Web service mocking, Web service inspection and Web service load test.
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