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Application Layer(Layer 7): This layer lies at the top of the OSI model. It enables the user, human or software to access the network. It is responsible for providing services to the user. High-level APIs including resource sharing, remote file access. Services provided by Application layer: Network Virtual terminal: A network virtual terminal is a software version of a physical terminal. This layer is responsible for facilitating the user to log on to a remote host through setting up network virtual terminal. File transfer, access, and management: It allows a user to access files    in a remote host(to make changes or read data), to retrieve files from a remote computer for use in the local computer 

Presentation Layer(Layer 6):  It is concerned with the syntax and semantics of the information exchanged between two systems, translation of data between a networking service and an application; including character encoding, data compression, and encryption/decryption.  Functions of the Presentation layer include: Translation: As different computers use different encoding systems, the Presentation layer is responsible for the interoperability between these different encoding methods. The Presentation layer at the sender changes the information from its sender dependent format to a common format. The Presentation layer at the receiving machine changes the common format into its receiver dependent format. Encryption: Encryption means sender transforms the original information to another form and sends the resulting message out over the network. Compression: Data compression reduces the number of bits contained in the information which is particularly important ...

Session Layer(Layer 5): This layer lies between the Transport layer and the Presentation layer. It allows users of different machines to set sessions between them. It establishes, maintains and synchronizes the interaction among communicating devices. It manages communication sessions, i.e. continuous exchange of information in the form of multiple back-and-forth transmissions between two nodes. The functions of the session layer are: Dialog Control: The session layer allows two systems to enter into a dialog. It allows the communication between the two processes in either half-duplex or full duplex. Synchronization: It allows long transmissions to resume after a checkpointing.

Transport Layer(Layer 4):  The transport layer is responsible for the delivery of an entire message from one process to another. It ensures that the whole message arrives intact and in order, overseeing both error control and flow control at the source-to-destination level.  Functions include: Service-point Addressing: Computers often run more than one program at the same time. For this reason, source-to-destination delivery means delivery not only from one computer(source) to another(receiver), but also from a specific process on one computer to a specific process on the other. The transport layer header, therefore, must include a type of address, called service point address(port address). The Network layer is responsible for sending each packet to the correct computer; the transport layer gets the message to the correct process on that computer. Segmentation and Reassembly: A message is divided into transmittable segments, each segment containing a sequence numbe...

Network Layer(Layer 3):  It is responsible for the source-to-destination delivery of packets across multiple links(networks).It is also responsible for structuring and managing a multi-node network, including addressing, routing, and traffic control. Functions include: Logical Addressing: IP addressing is defined at the Network Layer of the OSI model. This layer adds a header to the packet coming from the upper layer that, among other things, indicates the logical addresses of the sender and receiver. IP addressing is also known as logical addressing. Routing: When independent networks are connected together to create a large network, the connecting devices(routers/gateways) route the packets to their final destination. The decision which route/path should be followed to reach from source to destination is handled by the network layer. 

Data link Layer(Layer 2):  It makes the raw transmission facility, reliable and error-free to the upper layer. It is responsible for moving the frames from one hop to the next, reliable transmission of data frames between two nodes connected by a physical layer. Functions  include: Framing: This layer divides the stream of bits from the network layer and organizes into manageable data units called frames. Physical Addressing: The data link layer adds a header to the frame in order to define physical address of the sender or receiver of the frame, if the frames are to be distributed to the different systems on the network. Flow Control: If the data rate, at which the data is transmitted by the sender is greater than the rate at which data is received by the receiver, this layer imposes a flow control mechanism to prevent overwhelming the receiver. This prevents traffic jam at the receiver side. Error Control: This layer adds reliability to the phys...

Physical Layer(Layer 1): This is the lowest layer of the OSI model that physically gets connected to the communication channel. It is responsible for movements of individual bits from one node to next i.e. transmission and reception of raw bit streams over a physical medium. Functions include: Physical characteristics of interfaces and medium: The physical layer defines the characteristics of the interface between the devices and the transmission medium. Bit Representation: To be transmitted, the bits must be encoded into signals, so this layer is responsible for defining which type of encoding is to be used. Data Rate: Physical layer defines the number of bits which are to be sent each second. Bit Synchronization: It ensures synchronization between the sender and the receiver at the bit level. Physical Topology: It defines how the devices are connected to make a network. M ode of transmission  Physical layer is responsible for defining the transmission mo...