The presentation layer (Layer 6) ensures that the message is presented to the upper layer in a standardized format. It deals with the syntax and the semantics of the messages.The main functions of the presentation layer are as follows −It encodes the messages from the user dependent format to the common format and vice versa, for communication among dissimilar systems.It is responsible for data encryption and decryption of sensitive data before they are transmitted over common channels.It is also responsible for data compression. Data compression is done at the source to reduce the number of bits to be transmitted. It ... Read More

The session layer (layer 5) is responsible for establishing, managing, synchronizing and terminating sessions between end-user application processes.The main functions of the session layer are as follows −It works as a dialog controller. It allows the systems to communicate in either half-duplex or full-duplex mode of communication.It is responsible for token management. Through this, it prevents the two users to simultaneously attempt the same critical operation.It synchronizes communication. It adds synchronization points or checkpoints in data streams for long communications. This ensures that data streams up to the checkpoints are successfully received and acknowledged. In case of any failures, only ... Read More

The transport layer (Layer 4) is responsible for delivery of an entire message from an application program on the source device to a similar application program on the destination device.The main functions of the transport layer are as follows −It delivers a message from a specific process of one computer to a specific process in another computer. The transport layer adds a port address to the header of the data packet.It divides a message into smaller segments such that each segment contains a sequence number along with the port address. It ensures that the segments arrive correctly at the receiver’s ... Read More

The data link layer (Layer 2) converts the raw transmission facility provided by the physical layer to a reliable and error-free link.The main functions of the data link layer are as follows −It breaks up the stream of bits into data frames having sizes from a few hundred to a few thousand bytes.It ensures distribution of the frames to the different systems. For this, it adds a header to the frame containing the address of the sender and the receiver.In case of reliable connection, this layer ensures that the receiver sends an acknowledgement frame. In absence of acknowledgement frames, frame ... Read More

OSI or Open System Interconnection model was developed by International Standards Organization (ISO). It gives a layered networking framework that conceptualizes how communications should be done between heterogeneous systems. It has seven interconnected layers. The seven layers of the OSI Model are a physical layer, data link layer, network layer, transport layer, session layer, presentation layer, and application layer, as shown in the following diagram −The physical layer, data link layer and the network layer are the network support layers. The layers manage a physical transfer of data from one device to another. Session layer, presentation layer, and application layer ... Read More

In computer networks, reference models give a conceptual framework that standardizes communication between heterogeneous networks.The two popular reference models are −OSI ModelTCP/IP Protocol SuiteOSI ModelOSI or Open System Interconnection model was developed by International Standards Organization (ISO). It gives a layered networking framework that conceptualizes how communication should be done between heterogeneous systems. It has seven interconnected layers.The seven layers of the OSI Model are a physical layer, data link layer, network layer, transport layer, session layer, presentation layer, and application layer. The hierarchy is depicted in the following figure −TCP / IP PROTOCOL SUITETCP stands for Transmission Control Protocol, while ... Read More

A Connectionless service is a data communication between two nodes where the sender sends data without ensuring whether the receiver is available to receive the data. Here, each data packet has the destination address and is routed independently irrespective of the other packets. Thus the data packets may follow different paths to reach the destination. There’s no need to setup connection before sending a message and relinquish it after the message has been sent. The data packets in a connectionless service are usually called datagrams.Protocols for connectionless services are −Internet Protocol (IP)User Datagram Protocol (UDP)Internet Control Message Protocol (ICMP)Connectionless services ... Read More

A connection-oriented service is one that establishes a dedicated connection between the communicating entities before data communication commences. It is modeled after the telephone system. To use a connection-oriented service, the user first establishes a connection, uses it and then releases it. In connection-oriented services, the data streams/packets are delivered to the receiver in the same order in which they have been sent by the sender.Connection-oriented services may be done in either of the following ways −Circuit-switched connection: In circuit switching, a dedicated physical path or a circuit is established between the communicating nodes and then data stream is transferred.Virtual circuit-switched ... Read More

A protocol is a set of rules and conventions agreed upon and followed by the communicating entities for data communication. A protocol outlines the what, how and when of a communication.The three aspects of a protocol are −Syntax − It defines the format of data that is to be sent or received.Semantics − It defines the meaning of each section of bits that are transferred.Timings − It defines the time at which data is transferred as well as the speed at which it is transferred.Protocol HierarchiesMost networks are organized as a stack of layers, one on the top of another. ... Read More

Network software encompasses a broad range of software used for design, implementation, and operation and monitoring of computer networks. Traditional networks were hardware based with software embedded. With the advent of Software – Defined Networking (SDN), software is separated from the hardware thus making it more adaptable to the ever-changing nature of the computer network.Functions of Network SoftwareHelps to set up and install computer networksEnables users to have access to network resources in a seamless mannerAllows administrations to add or remove users from the networkHelps to define locations of data storage and allows users to access that dataHelps administrators and ... Read More