What is OSI(Open System Interconnection) Model?
° The OSI (Open Systems Interconnection) model is a theoretical framework that defines a networking standard for communication systems.
° OSI model was developed by the International Organization for Standardization (ISO) in 1984.
° And it is now considered as an architectural model for the inter-computer communications.
° It is a seven-layer reference model that describes how data is transmitted and processed within a computer network by breaking it down into smaller, manageable parts.
° Each layer serves a specific function, such as addressing, routing, or error correction, and interacts with the layers above and below it to provide a complete network solution.
° The OSI model provides a common reference point for understanding how data is transmitted and processed within a network, and it is not a standard itself.
° It is widely used as a guide for designing, implementing and troubleshooting communication systems and networks.
| OSI layered model in computer network skills arena |
Characteristics of OSI Model:
It has the following characteristics:
• Layered architecture: The OSI model is divided into seven distinct layers, each serving a specific function and interacting with the layers above and below it to provide a complete network solution.
• Modularity: Each layer of the OSI model has its own set of protocols and technologies that are used to transmit and process data, which allows for greater flexibility and scalability in network design.
• Independence: The OSI model allows network protocols and technologies to be developed, tested, and updated independently of each other, which makes it easier to add new features, fix bugs, and improve performance.
• Interoperability: The OSI model provides a common reference point for understanding how data is transmitted and processed within a network, which allows for greater interoperability between different systems and networks.
• Troubleshooting: The OSI model makes it easier to troubleshoot and diagnose problems in the network, as each layer can be examined and managed separately.
• Vendor independence: The OSI model is vendor-independent which means that different vendors can develop and implement products that conform to the same model.
• Functionality: Each layer of the OSI model provides a specific set of functionality,
Different 7(seven) Layers of OSI Model
The layers of the OSI model are:
1) Physical Layer
2) Data Link Layer
3) Network Layer
4) Transport Layer
5) Session Layer
6) Presentation Layer
7) Application Layer
1) Physical layer
The Physical Layer is the first layer of the OSI (Open Systems Interconnection) model. It deals with the physical properties of the network, such as voltage levels, signal timing, and cable types. It is responsible for the electrical, mechanical, and functional aspects of the connection between devices.
The main functions of the Physical Layer are:
• Transmission of bits: It is responsible for the physical transmission of data in the form of bits over the communication channel.
• Defining the physical characteristics of the interface: It defines the physical characteristics of the interface between the network and the device, such as the type of cable, connector, and voltage levels.
• Media access control: It controls the access to the shared media, such as Ethernet, Token Ring, and FDDI.
• Data rate and transmission mode: It defines the data rate and transmission mode, such as synchronous or asynchronous, for the communication channel.
• Topology: It defines the physical topology of the network, such as bus, star, or ring.
• Signal encoding: It defines the way the data is encoded into a signal that can be transmitted over the communication channel.
• Error detection: It provides a mechanism to detect errors in the transmission of bits, such as the use of parity bits or cyclic redundancy checks.
2) Data link layer
The Data Link Layer is the second layer of the OSI (Open Systems Interconnection) model. It is responsible for creating a reliable link between two devices on the same network.
The main functionality of the Data Link Layer are:
• Error Detection and Correction: The Data Link Layer checks for errors in the data that is transmitted between devices. It uses error detection techniques such as checksums, parity bits, and cyclic redundancy checks (CRCs) to detect errors, and it uses error correction techniques such as retransmission and forward error correction to correct errors.
• Flow Control: The Data Link Layer uses flow control techniques such as buffering, windowing, and congestion control to regulate the flow of data between devices. This ensures that data is transmitted at a rate that the receiving device can handle, and it also prevents data from being lost or delayed.
• Media Access Control: The Data Link Layer uses Media Access Control (MAC) protocols to control access to the shared communication medium, such as a wired or wireless network. It ensures that devices on the network can share the medium efficiently and without conflicts.
• Addressing: The Data Link Layer assigns a unique address to each device on the network. This address is used by the Network Layer to route data packets through the network.
• Encapsulation: The Data Link Layer encapsulates the data packets from the Network Layer into frames, which include addressing and error detection and correction information.
• Decapsulation: The Data Link Layer decapsulates the frames received from the network into data packets and pass them to the Network Layer for further routing.
3) Network layer
The Network Layer is the third layer of the OSI (Open Systems Interconnection) model. It is responsible for routing data packets through the network and for managing the logical addressing of devices on the network.
The main functionality of the Network Layer is as follows:
• Logical Addressing: The Network Layer assigns logical addresses to devices on the network, such as IP addresses. This allows data to be sent to specific devices on the network, rather than to a physical address.
• Routing: The Network Layer is responsible for routing data packets through the network. It uses routing algorithms to determine the best path for the data packets to take, and it uses routing tables to look up the next hop for each packet.
• Packet switching: The network layer is responsible for switching packets from the source to the destination based on the routing table.
• Flow Control: The Network Layer also controls the flow of data packets through the network, by implementing flow control mechanisms such as windowing, buffering and congestion control.
• Congestion Control: The Network Layer also monitors the network for congestion, and it can take measures to reduce the amount of traffic on the network, such as by discarding packets or by slowing down the flow of data.
• Error handling: The network layer also handles errors that may occur during packet transfer, such as lost packets or routing errors.
4) Transport layer
The Transport Layer of the OSI (Open Systems Interconnection) model is responsible for ensuring that data is delivered reliably and in the correct order between the source and destination devices. It deals with issues such as flow control, error recovery, and end-to-end delivery of data packets. The Transport layer provides a logical communication between end-user application processes running on different hosts. It also helps to hide the complex details of the underlying network from the upper layers.
The main functionalities of the Transport Layer are:
• Flow control: This feature allows the transport layer to manage the flow of data between the source and destination devices, ensuring that data is not sent too quickly for the destination device to handle.
• Error recovery: The transport layer provides mechanisms for error recovery, such as retransmitting lost or corrupted data packets, to ensure that data is delivered reliably.
• Segmentation: The transport layer is responsible for breaking up large data blocks into smaller segments that can be transmitted over the network.
• Multiplexing: This feature allows the transport layer to handle multiple communication sessions between different applications and devices simultaneously.
• Connection-oriented and Connectionless service: The transport layer can provide both connection-oriented and connectionless service. In a connection-oriented service, a virtual circuit is established between the source and destination devices before data is transmitted. In a connectionless service, data is sent without first establishing a virtual circuit.
• End-to-end communication: The transport layer provides a logical link between the end-user application processes running on different hosts. This enables end-to-end communication across the network.
5) Session layer
The Session Layer is the fifth layer of the OSI (Open Systems Interconnection) model. It is responsible for establishing, maintaining, and terminating connections between devices on a network. The main function of the session layer is to manage the communication sessions between applications. It provides the means for two devices to establish, maintain and terminate a logical connection.
The Session Layer is responsible for:
• Establishing a session: The Session Layer establishes a session between two devices by synchronizing the communication between them. This includes agreeing on the type of communication that will take place, and establishing any necessary security measures.
• Maintaining a session: The Session Layer maintains a session by ensuring that data is being transmitted correctly and that both devices are still communicating. It monitors the communication to detect any errors or problems and takes appropriate action.
• Terminating a session: The Session Layer terminates a session when the communication between the devices is finished. It releases any resources that were allocated for the session, and ensures that the session is properly closed.
The session layer also allows for multiplexing, which allows multiple logical connections to be multiplexed over a single physical connection. This means that multiple applications can use the same network connection at the same time, increasing the efficiency of the network.
It also provides dialog control, which allows applications to control the flow of data during a session. It can also provide authentication, which verifies the identity of the devices that are communicating, and it can also provide encryption, which ensures the confidentiality of the data being transmitted.
6) Presentation layer
The Presentation Layer of the OSI (Open Systems Interconnection) model is the sixth layer of the model. It is responsible for translating and formatting data for the Application Layer, which is the topmost layer of the OSI model. The main functionality of the Presentation Layer is to provide a common format for data representation so that data can be understood by the Application Layer, regardless of the format in which it was originally created.
The Presentation Layer's main functions are:
• Data compression: It is responsible for compressing data before it is sent across the network, in order to reduce the amount of bandwidth required to transmit it.
• Data encryption: It is responsible for encrypting data before it is sent across the network, in order to protect it from unauthorized access or tampering.
• Data conversion: It is responsible for converting data from one format to another, in order to ensure that it can be understood by the Application Layer. This includes converting between different character sets, image formats, and video formats.
• Data compression: It is responsible for compressing data before it is sent across the network, in order to reduce the amount of bandwidth required to transmit it.
7) Application layer
The Application Layer is the seventh and highest layer of the OSI (Open Systems Interconnection) model. It is the interface between the network and the applications that use it, and it provides a common set of services to the applications that use the network. The Application layer is responsible for providing the necessary functions to support the various types of applications that use the network, such as file transfer, remote login, email, and other types of communications.
The main functionality of the Application Layer includes:
• Identifying and establishing communication partners: It identifies and establishes communication partners for the application, such as determining the availability of a remote server.
• Synchronizing communication: It synchronizes communication between the application and its communication partner.
• Managing errors: It manages errors that occur during communication, such as ensuring that all data is received correctly.
• Negotiating options: It negotiates options and parameters for the communication, such as security options and data compression.
• Identifying network services: It allows applications to identify the network services they require, such as email or file transfer.
• Network Virtual Terminals: It provides support for Network Virtual Tarminals (NVTs) which are used for remote login and other types of remote access to network resources.
• File transfer and management: It provides support for file transfer and management, such as file upload and download.
• Database access: It provides support for database access, such as SQL (Structured Query Language) used for communicating with databases.
______________________________________
Please share this post and blog link with your friends.For more programs use this blog.
If you have any problem, please comment in comment box, subscribe this blog for notifications of new post on your email and follow this blog.If you have any methodHh of this program or want to give any suggestion send email on hc78326@gmail.com
Created by-- HARSH CHAUHAN
