OSI MODEL
OSI (Open System Interconnection) model is the conceptual model it characterizes and standardizes the communication function of telecommunication.
In the OSI MODEL seven layer are describing with different function of data travel through network.
There are the Seven layers of the OSI Model.
⦁ Apllication Layer
⦁ Presentation Layer
⦁ Session Layer
⦁ Transport Layer
⦁ Network Layer
⦁ Data Link layer
⦁ Physical Layer
1. Physical Layer:-
Physical layer is the Lower layer of OSI Model, Physical layer define the How the Bits of data are transfer from one device to another device. In the Physical Layer Network cables and network cards working and send or received the data. It is consist the networking hardware transmission of a network. This layer work with the physical connection like Cable wireless transmission, connector and interface card as per the network requirements.
- Representation of Bits:-
Physical layer are consists of the data streaming. These data must be encoded into signals for transmission. It defines the data type encoding in 0's and 1's are changed into signal.
2. Date Rate:-
Physical layer defines the rate of transmission of data which is the number of data bits as per second are transmitted.
3. Synchronization:-
The synchronization of the data transmission and receiver .The sender and receiver are synchronized the data at the bit level.
4. Interface:-
The physical layer defines the transmission interface between devices and transmission media.
5. Line Configuration:-
Physical layer connect the devices with transmission media Point to Point configuration and Multi point configuration.
6. Topologies:-
Devices must be connected using the following topologies like Bus topologies, Ring Topologies, Star Topologies, Mesh Topologies.
7. Transmission Modes:-
Physical Layer defines the direction of transmission between the devices Simplex, Half Duplex, Full Duplex.
2. DATA LINK LAYER:-
The data link layer is the second layer of the OSI Model. The data link layer provide the transferring the data in the form of frames one layer to another layer. The physical layer allow the above layers to assume virtually data frames transmission over the link.
There are two types of Data Link layer:-
⦁ Logical Link Control :- The Logical Control used to flow control of data Bits and error detection.
⦁ Media Access Control:- The Media Access used for hardware addressing and controlling the access method.
FUNCTIONS OF DATA LINK LAYER:-
1. Framing:-
Frames are the streams of bits received data from the network layer. This division of stream of data bits is done by Data Link Layer.
2. Physical Addressing:-
The Data Link layer add a header into the frame. Physical address of the sender or receiver of the data bits frames, if the frames are to be distributed to different systems on the network.
3. Flow Control:-
A flow control mechanism to avoid a fast transmitter from running a slow receiver by buffering the extra bits is provided by flow control. This prevents traffic jam at the receiver side.
4. Error Control:-
Error control is achieved by adding a trailer at the end of the frame. Duplication of frames are also prevented by using this mechanism. Data Link Layers adds mechanism to prevent duplication of frames.
5. Access Control:-
Protocols of this layer determine which of the devices has control over the link at any given time, when two or more devices are connected to the same link.
3. Network Layer:-
Network layer is third layer of the OSI Model. Network layer is responsible for forwarding the packets of data and control the operation of subnet and addressing, routing and decided the path of data should be on network condition. And Logical device addressing is used to identify a host on a network.
FUNCTIONS OF NETWORK LAYER:-
- It translates logical network address into physical address. Concerned with circuit, message or packet switching.
- Routers and gateways operate in the network layer. These Mechanism is provided by Network Layer for routing the packets to final destination.
- Connection services are provided including network layer flow control, network layer error control and packet sequence control.
- Breaks larger packets into small packets.
4. Transport layer:-
Transport layer is the fourth layer of OSI Model. Transport layer is the responsible for end to end communication over a network. The Transport layer process the data received from the higher level layer and control the flow data and data recovery. The Transport layer is responsible for the management of error correction, providing quality and reliability to the end user. and transport layer enables the host to send and receive error corrected data, packet or messages over a network.
FUNCTIONS OF TRANSPORT LAYER:-
1. Service Point Addressing:-
Transport Layer header includes the service point address which is port address. This layer gets the message to the correct process on the computer unlike Network Layer, which gets each packet to the correct computer.
2. Segmentation and Reassembling:-
A message is divided into segments, each segment contain the sequence of number. Message is reassembled correctly upon arrival at the destination and replaces packets which were lost in transmission.
5. Session Layer:-
Session Layer is fifth layer of the OSI Model. Session Layer allow the session establishment and terminate a session between two system. Session layer manages and synchronize the conversation between two different applications. Transfer of data from one destination to another destination of session layer streams of data are marked and are re synchronized properly, so that the ends of the messages are not cut prematurely and data loss is avoided.
FUNCTIONS OF SESSION LAYER:-
1. Dialog Control :-
This layer allows two systems to start communication with each other in half-duplex or full-duplex.
2. Synchronization:-
This layer allows a process to add checkpoints which are considered as synchronization points into stream of data.
6. Presentation layer:-
Presentation layer define data format to be presented to the application layer. And Compression and encryption data used on Presentation layer. The primary goal of this layer is to take care of the syntax and semantics of the information exchanged between two communicating systems.
FUNCTIONS OF PRESENTATION LAYER:-
1. Translation :
Information in the form of characters and numbers should be changed to bit streams. The presentation layer is responsible for interoperability between encoding methods as different computers use different encoding methods. It translates data between the formats the network requires and the format the computer.
2. Encryption :-
It carries out encryption at the transmitter and decryption at the receiver.
3. Compression :-
It carries out data compression to reduce the bandwidth of the data to be transmitted. The primary role of Data compression is to reduce the number of bits to be transmitted. It is important in transmitting multimedia such as audio, video, text etc.
7. Application Layer:-
The Application layer is the closest layer to user. It consist of protocol to focus on process to process communication across IP network and provide the communication interface end user services. Manipulation of data (information) in various ways is done in this layer which enables user or software to get access to the network. Some services provided by this layer includes: E-Mail, transferring of files.
FUNCTIONS OF APPLICATION LAYER:-
1. Mail Services:-
This layer provides the basis for E-mail forwarding and storage.
2. Network Virtual Terminal:-
It allows a user to log on to a remote host. The application creates software emulation of a terminal at the remote host. User's computer talks to the software terminal which in turn talks to the host and vice versa. Then the remote host believes it is communicating with one of its own terminals and allows user to log on.
3. Directory Services:-
This layer provides access for global information about various services. File Transfer, Access and Management (FTAM) : It is a standard mechanism to access files and manages it. Users can access files in a remote computer and manage it. They can also retrieve files from a remote computer.
TCP/IP Model:-
TCP/IP stand for Transmission Control Protocol/Internet Protocol is set of networking protocols allow two or more computer to communicate in private network.
TCP/IP Model consist of four layer.
⦁ Application layer
⦁ transport Layer
⦁ Internet Layer
⦁ Network Access Layer
The application, presentation and Session layer of the OSI Model are merged in only one layer, Application layer in the TCP/IP Model. Physical layer and data link layer are called network Access layer in the TCP/IP model.
Lowest layer of the all. Protocol is used to connect to the host, so that the packets can be sent over it. Varies from host to host and network to network.
2. Internet Layer:-
Selection of a packet switching network which is based on a connection less internet work layer is called a internet layer.
3. Transport Layer:-
It decides if data transmission should be on parallel path or single path. Functions such as multiplexing, segmenting or splitting on the data is done by transport layer. The applications can read and write to the transport layer.
4. Application Layer:-
The TCP/IP specifications described a lot of applications that were at the top of the protocol stack. Some of them were TELNET, FTP, SMTP, DNS etc.
Difference b/w OSI and TCP/IP
OSI (Open System Interconnection):-
⦁ OSI is protocol independent standard acting as a communication gateway between network and end user
⦁ OSI model the transport layer guarantees the delivery of packets.
⦁ OSI follow the vertical approach.
⦁ OSI has a separate Presentation layer and Session layer.
⦁ OSI model are used the guidance tool.
TCP/IP:-
⦁ TCP/IP is based on the standard protocol around the internet developed. It allow the connection of hosts over a network.
⦁ TCP/IP model the transport layer not gurantees delivery of packet.
⦁ TCP/IP follow the Horizontal approch.
⦁ TCP/IP does not have the saparate presentation layer and session layer
⦁ TCP/IP is implementation of the OSI model.
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