ISO=International Organization for Standardization
OSI=Open System International
The OSI was model meant to help vendors create interoperable network devices and software in the form of protocols, so that different vendor s networks could work with each other and it was introduced by ISO. By this help of OSI model can communicate.
:&different manufactures PCs
:&different hardware configuration
:&different software
:&Protocol support
OSI model is the primary architectural model for networks. It describes how data and network information are communicated from an application on one computer through the network. A reference model is a conceptual blue print of how communication should take place between two computers. It addresses all the process required for effective communication and divides the process into logical grouping called layers. In OSI, concept total communication process has divided in to 7 layers. Based on hardware or software supports seven layers have divided in to two.
1. Upper layer
Upper layer works based on software or operating system and in each upper layer data known as protocol data unit (PDU) such as Application Protocol Data unit, Presentation Protocol data unit etc.,
2. Lower layer
Lower Layers works based on hardware components. The main function of upper layer is to send, formatted data from source to destination with some added information (headers). In each lower layer data identified with different names such as segment (in transport layer), packet (in network layer), frame (in data link layer) and bits (in physical layer).
Encapsulation:-
The process of adding protocol headers with data is known as encapsulation.
De-encapsulation:-
The process of removing protocol headers from data is known as de-encapsulation. In communication system source devices takes place encapsulation and destination devices takes place de-encapsulation.
1.APPLICATION LAYER:
When an application program runs our application (eg: www.yahooo.com) the request is handover to the application layer. It is the layer, which interacts with user directly, receives application from the user. Data communication starts from these layers. Its function is to check data availability (ie., checks whether www.yahoo.com is available or not) and if the data exists transfer data to presentation layer. (in detail: link)Protocol support in Application Layer
" HTTP Hyper text transfer protocol2.PRESENTATION LAYER
This layer Encryption or decryption Compression and Decompression takes place in this layer. The output of presentation layer is presentation PDU.It translates data to common formats such as
* MPEG => moving picture Expert group