However, the OSI 7-layer model is still widely used, as it helps visualize and communicate how networks operate, and helps isolate and troubleshoot networking problems. OSI was introduced in by representatives of the major computer and telecom companies, and was adopted by ISO as an international standard in The application layer is used by end-user software such as web browsers and email clients. It provides protocols that allow software to send and receive information and present meaningful data to users.
The presentation layer prepares data for the application layer. It defines how two devices should encode, encrypt, and compress data so it is received correctly on the other end.
The presentation layer takes any data transmitted by the application layer and prepares it for transmission over the session layer. The session layer creates communication channels, called sessions, between devices. It is responsible for opening sessions, ensuring they remain open and functional while data is being transferred, and closing them when communication ends. The session layer can also set checkpoints during a data transfer—if the session is interrupted, devices can resume data transfer from the last checkpoint.
It is responsible for reassembling the segments on the receiving end, turning it back into data that can be used by the session layer. The transport layer carries out flow control, sending data at a rate that matches the connection speed of the receiving device, and error control, checking if data was received incorrectly and if not, requesting it again. The network layer has two main functions. One is breaking up segments into network packets, and reassembling the packets on the receiving end.
The other is routing packets by discovering the best path across a physical network. The network layer uses network addresses typically Internet Protocol addresses to route packets to a destination node. The data link layer establishes and terminates a connection between two physically-connected nodes on a network.
It breaks up packets into frames and sends them from source to destination. This layer is composed of two parts—Logical Link Control LLC , which identifies network protocols, performs error checking and synchronizes frames, and Media Access Control MAC which uses MAC addresses to connect devices and define permissions to transmit and receive data.
The physical layer is responsible for the physical cable or wireless connection between network nodes. It defines the connector, the electrical cable or wireless technology connecting the devices, and is responsible for transmission of the raw data, which is simply a series of 0s and 1s, while taking care of bit rate control.
It divides data communication into seven abstraction layers and standardizes protocols into appropriate groups of networking functionality to ensure interoperability within the communication system regardless of the technology type, vendor, and model. The OSI model was originally developed to facilitate interoperability between vendors and to define clear standards for network communication. This image illustrates the seven layers of the OSI model. The lowest layer of the OSI model is concerned with data communication in the form of electrical, optic, or electromagnetic signals physically transmitting information between networking devices and infrastructure.
The physical layer is responsible for the communication of unstructured raw data streams over a physical medium. It defines a range of aspects, including:. The second layer of the OSI model concerns data transmission between the nodes within a network and manages the connections between physically connected devices such as switches. The raw data received from the physical layer is synchronized and packaged into data frames that contain the necessary protocols to route information between appropriate nodes.
The data link layer is further divided into two sublayers:. The network layer is responsible for routing the data via the best physical path based on a range of factors including network characteristics, best available path, traffic controls , congestion of data packets, and priority of service, among others.
The network layer implements logical addressing for data packets to distinguish between the source and destination networks. Other functions include encapsulation and fragmentation , congestion controls, and error handling.
The outgoing data is divided into packets and incoming data is reassembled into information that is consumable at a higher application level. Network layer hardware includes routes, bridge routers, 3-layer switches, and protocols such as Internet IPv4 Protocol version 4 and Internet Protocol version 6 IPv6.
As the first of three layers that deal with the software level, the session layer manages sessions between servers to coordinate communication. Session refers to any interactive data exchange between two entities within a network.
Common examples include HTTPS sessions that allow Internet users to visit and browse websites for a specific time period. The Session Layer is responsible for a range of functions including opening, closing, and re-establishing session activities, authentication and authorization of communication between specific apps and servers, identifying full-duplex or half-duplex operations, and synchronizing data streams.
The sixth layer of the OSI model converts data formats between applications and the networks. Responsibilities of the presentation layer include:. It also performs sequencing and reassembling of the segmented data. The functions of the transport layer are :. This type of transmission is reliable and secure. Connectionless service: It is a one-phase process and includes Data Transfer. In this type of transmission, the receiver does not acknowledge receipt of a packet. This approach allows for much faster communication between devices.
Connection-oriented service is more reliable than connectionless Service. It is a part of the OS and communicates with the Application Layer by making system calls.
Session Layer Layer 5 : This layer is responsible for the establishment of connection, maintenance of sessions, authentication, and also ensures security. The functions of the session layer are : Session establishment, maintenance, and termination: The layer allows the two processes to establish, use and terminate a connection. Synchronization: This layer allows a process to add checkpoints which are considered synchronization points into the data.
These synchronization points help to identify the error so that the data is re-synchronized properly, and ends of the messages are not cut prematurely and data loss is avoided. Dialog Controller: The session layer allows two systems to start communication with each other in half-duplex or full-duplex. These are also known as Upper Layers or Software Layers. Presentation Layer Layer 6 : The presentation layer is also called the Translation layer. The data from the application layer is extracted here and manipulated as per the required format to transmit over the network.
The encrypted data is known as the ciphertext and the decrypted data is known as plain text. A key value is used for encrypting as well as decrypting data.
Compression: Reduces the number of bits that need to be transmitted on the network. These applications produce the data, which has to be transferred over the network. This layer also serves as a window for the application services to access the network and for displaying the received information to the user. Ex: Application — Browsers, Skype Messenger, etc. This article is contributed by Kundana Thiyari and Harshita Pandey. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.
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