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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 number. These

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 physical layer by addin

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 modes.

The OSI(Open System Interconnection) model is a layered framework to implement protocols. It consists of seven separate but related layers, each of which defines a part of the process of moving information across a network.  The International Standards Organisation(ISO) developed the Open Systems Interconnection(OSI) model .  An open system is a set of protocols that allows any two different systems to communicate regardless of their underlying architecture. The OSI model is not a protocol. It is a model for understanding and designing a network architecture that is flexible, robust and interoperable. The Seven Layers of OSI are:- 7.Application 6.Presentation 5.Session 4.Transport 3.Network 2.Data Link 1. Physical

What is a Network ? A Network is defined as an arrangement of a set of devices connected together by communication links for the purpose of sharing data. Each device may be called as a node which can be a computer, printer or any other devices capable of sending or receiving data generated by other nodes or devices on the network. Following are the types of Network:- 1. Local Area Network(LAN): LANs are privately owned networks defined within a small physical area such as in a single office, building or campus. LAN size is limited to a few kilometers for which the network management is simple.   Most common LAN topologies are bus, ring, star and have data rates in the range of 4 to 16 megabits per second. LANs often use a transmission technology consisting of a single cable to which all the machines are attached. LANs are mostly used to allow resources to be shared among personal computers or workstations. 2. Metropolitan Area Network(MAN): A MAN is designed to

Modes of Data Communication refers to the direction of data flow from sender to receiver or vice-versa. There are basically three modes of data communication:- 1. Simplex: In this mode the communication is unidirectional . Only one of the two devices on a link can transmit and the other can only receive .i.e data travels in one direction. Example: radio, television, loudspeaker 2. Half-Duplex: In this mode, each device on the link has   the ability to both transmit and receive, each at a time . When one device is sending, the other can only receive and vice versa. Example: walkie-talkie 3. Full-Duplex: In full-duplex mode, both the devices can transmit and receive simultaneously .i.e data can travel in both directions at the same time. Here the communication is bidirectional . Example: Telephone

Data Communication refers to the exchange of data between the sender and the receiver.There are basically five elements of data communication:- 1. Message: It is the information or the data to be communicated.It may be in the form of text, numbers, pictures, sound, video or any other physical quantities. 2. Sender: It is the device which sends the data.It can be computers, workstations, telephone etc. 3. Receiver: It is the device which receives the message.It can be computers, workstations, television etc. 4. Transmission Medium: It is the physical path by which the message travels from sender to the receiver.It could be a twisted pair cable, fibre optic cable, microwaves, infrared waves etc. 5. Protocol : A protocol is a set of rules that govern data communications. It establishes an agreement between the communicating devices. Without a protocol, two devices may be connected but cannot communicate with each other. The protocols are being embedded with the co