Following are the different layers in the OSI model:

Physical Layer: The physical layer is the lowest layer in the OSI reference model. It is in charge of establishing a physical connection between the devices. BITS of information are stored in the physical layer. Following are the responsibilities of the physical layer :

• Bit synchronisation: A clock is provided by the physical layer, which allows the bits to be synchronised. This clock controls both the sender and the receiver, ensuring bit-level synchronisation.
• The transmission rate, or the number of bits transferred per second, is likewise defined by the Physical layer.
• Physical topologies: The physical layer defines the arrangement of devices/nodes in a network, such as bus, star, or mesh topologies.
• Transmission mode: The physical layer also specifies how data is passed between the two linked devices. Simplex, half-duplex, and full-duplex transmission modes are available.

Data Link Layer (DLL): The data link layer is in charge of message transport from node to node. The major purpose of this layer is to ensure that data transfers from one node to another through the physical layer are error-free. Following are the responsibilities of data link layer :

• Framing: The data link layer is responsible for framing. It allows a sender to deliver a set of bits to a receiver that are relevant to the receiver. This can be done by attaching unique bit patterns to the frame's beginning and end.
• Physical addressing: After producing frames, the Data link layer adds the sender and/or receiver's physical addresses (MAC addresses) to the header of each frame.
• Error control: The data link layer implements error control by detecting and retransmitting broken or lost frames.
• Flow Control: Because the data rate on both sides must be consistent or the data would be corrupted, flow control coordinates the amount of data that can be transferred before acknowledgment.
• When many devices share a single communication channel, the MAC sub-layer of the data link layer assists in determining which device has control over the channel at any particular time.

Network Layer: The network layer is responsible for data transmission between hosts on different networks. Following are the responsibilities of the network layer :

• Routing: From source to destination, the network layer protocols determine which path is best. Routing is the name for this network layer function.
• The network layer defines an addressing scheme in order to uniquely identify each device on the internetwork. The network layer places the IP addresses of the sender and receiver in the header. An address like this recognises each gadget in a unique and universal way.

Transport Layer: The transport layer delivers services to the application layer while also receiving services from the network layer. Segments are the units of data in the transport layer. Following are the responsibilities of the Transport layer :

• This layer accepts the message from the (session) layer and splits it down into SMALLER parts. A header is attached to each of the segments created. The message is reassembled by the transport layer at the destination station.
• The transport layer header provides a form of address called service point address or port address in order to deliver the message to the relevant process. The transport layer ensures that the message is delivered to the relevant process by supplying this address.

Session Layer: The Session Layer is in charge of establishing connections, maintaining sessions, authenticating users, and ensuring security. Following are the responsibilities of session layer :

• Establishing, maintaining, and terminating a session: The layer enables the two processes to create, use, and terminate a connection.
• Synchronization: This layer allows a process to insert checkpoints into the data that serve as synchronisation POINTS. These synchronisation points aid in the detection of errors so that data may be correctly resynchronized, message ends are not SEVERED prematurely, and data loss is avoided.
• Dialog Controller: The session layer enables two systems to communicate in half-duplex or full-duplex mode.

Presentation Layer: The Presentation Layer is often referred to as the Translation Layer. The data from the application layer is retrieved and processed here so that it may be transmitted across the network in the proper format. Following are the responsibilities of the presentation layer :

• It is responsible for translations such as ASCII to EBCDIC.
• Encryption/decryption: Data encryption is the process of converting data into a different form or coding. The CIPHERTEXT is the encrypted data, and the plain text is the decoded data. When encrypting and decrypting data, a key-value is used.
• Compression: This technique reduces the amount of data that must be transmitted over the network.

Application Layer: The Application layer, which is implemented by network applications, is at the very top of the OSI Reference Model stack of levels. Following are the responsibilities of the application layer :

• This layer also acts as a window for application services to connect to the network and show the information they receive to the user.
• It is also responsible for file transfer access and management.
• It is responsible for mail services.
• It is also responsible for directory services.