OSI Model

OSI Reference Model (Open System Interconnection)

The open system interconnection model is a conceptual framework for understanding various aspects of a computer network into seven layers  It has been developed by International Organization of Standardization (ISO) in year 1974. It maintained a ISO/IEC 7498-1. Each layer having special functionality. All layers working together to transmit the data for one end to another end 

Above mentioned seven layers can divide into 3 categories. It is the

•       Software layer- [application, presentation, session layers]
•       Transport layer [heart of OSI]
•       Hardware layers [network, datalink, physical layers]

Why a layer network model

•          Reduce complexity
•           Standardize interface
•           Facilitate modular engineering.
•           Ensure inter operable technology.
•           Simplifies teaching and learning.
•           To allow different type of network hardware and software to communicate with each other.
•           When we make the network devises OSI model is very important.
•           To design network.
•           To detect the errors of network.
•           To breaks network communication into smaller parts that are easy to develop.

OSI LAYERS

                                               

   01.Physical Layer

•          The bottom layer of the OSI model.
•           It is a protocol to decide physical signals and connection methods in networks.
•           Working the interface between communication media and communication devises.
•           The way off cable is connected to the network interface, size of connector type and number of pins and modulation technology is describing in this layer.\

    02.Data Link Layer

•  Most important function is it provide a way for packets to be sent safely over the physical media without interference from other devices.
•  It realizes the reliable transmission between two points based on MAC (Media Access Control) address. (transmit data between LAN or WAN network ports.)
• Data link layer provide basic error detection and correction to ensure that data sent is the same as the data receive
• The data from the network layer will be transmitted and framed into the physical layer to distribute trough the network.
• Data link layer support to flow control and frame synchronization.
• Data link layer commonly used bridge and switches.

     03.Network Layer

• The ultimate responsibility is to determine the best way to send data to the end point and it decides appropriate communication path between two hosts based IP addresses.
• To above purpose, logical addressing use for translate logical address to MAC (Media Access Control) address.
• Only decides communication path and is not involved in the quality of communication.
• Network layer provide two important functions. It is logical addressing and routing. 

     04.Transport Layer

•  Provide basic data transfer services.
•  TCP helps IP to move the data packet to one end to another end.
•   Main purpose of the transport layer is handle error recovery it ultimately ensures data are received in order and free of corruption.
•   Ensure complete data transferring.

     05.Session Layer

• The session layer establishes conversation sessions between networked devices. Session layer be able to detect the errors of above layers.
• Session layer tracks the dialogs between computers, which are also called sessions 
• Session layer allows three types of transmission medias.

1.      Simplex – data flow to only one direction.

2.      Half-duplex – both way communication but at a time

3.      Full duplex – both way communication at the same time. 

 

     
     06.Presentation Layer

• Presentation layer can data Translate, Encryption and Compression
• It responsible for how data is represented to application layer.
• translate: convert the sender data to the public data and also public data type convert to the sender data type.
• Encryption: the sender will translate the original data into another format to send the data foe receiver (it is security method to the data protection)
• Compression: number of bits in the data is reduced. It is important for multimedia transport and also when we sending the large file to the receiver.

    07.Application Layer

•          The most recent layer is for the user.
•          Application layer represents the programing interfaces that application programs use to request network services.
•          Provide an interface to user services of e-mail, telnet, FTP and HTTP.
•          Application layer can data recovery procedure and error recovery procedures.
•          Ensure the privacy
•          More than is protocols are used in this layer