January 27, 2020
Amitraj
OSI Model in Computer Network
-> OSI Model stands for Open System interconnection model.
-> OSI Model defines how data is transferred from one computer to another computer.
-> In a very basic scenario two computers connected with a LAN and connectors transfer data using the NIC. This forms a computer network, however if both the system uses different operating systems, for example one system runs on windows and other one runs on MacOS then how can data be transferred between these two different systems, here comes the role of a OSI model which is a seven layered model that defines how a data can be transferred between different systems.
-> OSI model was introduced by International Organisation for standardisation (ISO) in 1984.
-> This model defines seven separate layers.
Characterstics of the OSI Model -
The OSI model is divided into two layers: upper layers and lower layers
-> The upper layer of the OSI model mainly deals with the application related issues, and they are implemented only in the software. Both the end user and the application layer interact with the software applications.
-> The lower layer of the OSI model deals with the data transport issues. The data link layer and the physical layer are implemented in hardware and software.The physical layer is mainly responsible for placing the information on the physical medium.
There are the Seven layers in OSI Model listed below:-
1.Application Layer
2.Presentation Layer
3.Session Layer
4.Transport Layer
5.Network Layer
6.Data-Link Layer
7.Physical Layer
1. Application Layer:-
-> The application layer is the layer that the users and user-applications most often interact with.
-> An application layer serves as a window for users and application processes to access network service.
-> It handles issues such as network transparency, resource allocation, etc.
-> Network communication is discussed in terms of availability of resources, partners to communicate with, and data synchronization.
2. Presentation Layer:-
-> The presentation layer is responsible for mapping resources and creating context. It is used to translate lower level networking data into data that applications expect to see.
-> Presentation layer receives the data from top most layer which is application layer.
-> This layer is a part of the operating system that converts the data from one presentation format to another format.
-> The Presentation layer is also known as the syntax layer.
3. Session Layer:-
-> The session layer is a connection handler. It creates, maintains, and destroys connections between nodes in a persistent way.
-> The main role of session layer is to setup and maintain the connection between different systems.
4. Transport Layer:-
-> The main role of transport layer is to check the reliability of data communication.
-> It receives the data from the upper layer and converts them into smaller units known as segments.
-> This layer can also called end-to-end layer as it provides a point-to-point connection between source and destination to deliver the data reliably.
In this layer two Protocols that are:
Transmission Control Protocol
-> It is a standard protocol that allows the systems to communicate over the internet.
-> It establishes and maintains a connection between hosts.
-> When data is sent over the TCP connection, then the TCP protocol divides the data into smaller units known as segments. Each segment travels over the internet using multiple routes, and they arrive in different orders at the destination. The transmission control protocol reorders the packets in the correct order at the receiving end.
User Datagram Protocol
-> User Datagram Protocol is a transport layer protocol.
-> It is an unreliable transport protocol as in this case receiver does not send any acknowledgment when the packet is received, the sender does not wait for any acknowledgment. Therefore, this makes a protocol unreliable.
5. Network Layer:-
-> The Data link layer is responsible for routing and forwarding the packets.
-> The main purpose of network layer is to receive the data segments from transport layer and transfer them from one computer to another computer on different network.
-> This layer manages device addressing, tracks the location of devices on the network.
-> The protocols used to route the network traffic are known as Network layer protocols. Examples of protocols are IP and Ipv6.
6. Data Link Layer:-
-> Data link layer receives the data from network layer.
-> This layer is responsible for the error-free transfer of data frames.
-> It provides a reliable and efficient communication between two or more devices.
-> This layer is responsible for the error-free transfer of data frames.
There are two types of addressing done to the packets transfers from one computer to another computer.
Logical addressing: Logical addressing is assigning sender and receiver IP addresses to data packets. This is done at the network layer.
Physical addressing: Physical addressing is done at data link layer where MAC addresses of sender and receiver are assigned to each data packets.
7. Physical Layer:-
-> The physical layer is responsible for handling the actual physical devices that are used to make a connection. This layer involves the bare software that manages physical connections as well as the hardware itself (like Ethernet).
-> It is the lowest layer of the OSI model.
-> It establishes, maintains and deactivates the physical connection.
-> It specifies the mechanical, electrical and procedural network interface specifications.
-> OSI Model stands for Open System interconnection model.
-> OSI Model defines how data is transferred from one computer to another computer.
-> In a very basic scenario two computers connected with a LAN and connectors transfer data using the NIC. This forms a computer network, however if both the system uses different operating systems, for example one system runs on windows and other one runs on MacOS then how can data be transferred between these two different systems, here comes the role of a OSI model which is a seven layered model that defines how a data can be transferred between different systems.
-> OSI model was introduced by International Organisation for standardisation (ISO) in 1984.
-> This model defines seven separate layers.
Characterstics of the OSI Model -
The OSI model is divided into two layers: upper layers and lower layers
-> The upper layer of the OSI model mainly deals with the application related issues, and they are implemented only in the software. Both the end user and the application layer interact with the software applications.
-> The lower layer of the OSI model deals with the data transport issues. The data link layer and the physical layer are implemented in hardware and software.The physical layer is mainly responsible for placing the information on the physical medium.
There are the Seven layers in OSI Model listed below:-
1.Application Layer
2.Presentation Layer
3.Session Layer
4.Transport Layer
5.Network Layer
6.Data-Link Layer
7.Physical Layer
1. Application Layer:-
-> The application layer is the layer that the users and user-applications most often interact with.
-> An application layer serves as a window for users and application processes to access network service.
-> It handles issues such as network transparency, resource allocation, etc.
-> Network communication is discussed in terms of availability of resources, partners to communicate with, and data synchronization.
2. Presentation Layer:-
-> The presentation layer is responsible for mapping resources and creating context. It is used to translate lower level networking data into data that applications expect to see.
-> Presentation layer receives the data from top most layer which is application layer.
-> This layer is a part of the operating system that converts the data from one presentation format to another format.
-> The Presentation layer is also known as the syntax layer.
3. Session Layer:-
-> The session layer is a connection handler. It creates, maintains, and destroys connections between nodes in a persistent way.
-> The main role of session layer is to setup and maintain the connection between different systems.
4. Transport Layer:-
-> The main role of transport layer is to check the reliability of data communication.
-> It receives the data from the upper layer and converts them into smaller units known as segments.
-> This layer can also called end-to-end layer as it provides a point-to-point connection between source and destination to deliver the data reliably.
In this layer two Protocols that are:
Transmission Control Protocol
-> It is a standard protocol that allows the systems to communicate over the internet.
-> It establishes and maintains a connection between hosts.
-> When data is sent over the TCP connection, then the TCP protocol divides the data into smaller units known as segments. Each segment travels over the internet using multiple routes, and they arrive in different orders at the destination. The transmission control protocol reorders the packets in the correct order at the receiving end.
User Datagram Protocol
-> User Datagram Protocol is a transport layer protocol.
-> It is an unreliable transport protocol as in this case receiver does not send any acknowledgment when the packet is received, the sender does not wait for any acknowledgment. Therefore, this makes a protocol unreliable.
5. Network Layer:-
-> The Data link layer is responsible for routing and forwarding the packets.
-> The main purpose of network layer is to receive the data segments from transport layer and transfer them from one computer to another computer on different network.
-> This layer manages device addressing, tracks the location of devices on the network.
-> The protocols used to route the network traffic are known as Network layer protocols. Examples of protocols are IP and Ipv6.
6. Data Link Layer:-
-> Data link layer receives the data from network layer.
-> This layer is responsible for the error-free transfer of data frames.
-> It provides a reliable and efficient communication between two or more devices.
-> This layer is responsible for the error-free transfer of data frames.
There are two types of addressing done to the packets transfers from one computer to another computer.
Logical addressing: Logical addressing is assigning sender and receiver IP addresses to data packets. This is done at the network layer.
Physical addressing: Physical addressing is done at data link layer where MAC addresses of sender and receiver are assigned to each data packets.
7. Physical Layer:-
-> The physical layer is responsible for handling the actual physical devices that are used to make a connection. This layer involves the bare software that manages physical connections as well as the hardware itself (like Ethernet).
-> It is the lowest layer of the OSI model.
-> It establishes, maintains and deactivates the physical connection.
-> It specifies the mechanical, electrical and procedural network interface specifications.
