Diploma in Computer Applications (DCA)


The Network bus topology connects all the nodes on a network to a main cable called bus. In this each packet that is placed on the bus contains the address of the destination node and is transmitted in both directions along the bus. As single high capacity cable is required thus requiring minimum cabling and its cost. Entire cable setup needs to be reconfigured to add a node. Time consuming process to troubleshoot as every point needs to be checked to locate the fault. The star topology connects nodes over a network using a central control unit called the hub. Nodes to a star-based network can be easily attached to the hub. All the nodes are connected to the hub thus requiring lot of cabling and cost. A faulty hub can disrupt the entire network. The ring topology connects the nodes on a network through a point-to-point connection. Easy to locate cable faults in a ring and the entire network stops functioning , if any of the nodes in the network malfunctions. OSI (Open System Interconnection) Model was design by International Organization for Standardization. The OSI model provides a global set of rules that make various manufacturers and developers to create software and hardware that is compatible with each other, which can make organized communications. As Network professional it helps us to understand and develop computer-to-computer communications over a network. This model divides network communications into seven layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application. It is the top most, seventh layer of the OSI Model. It makes easy communication between software application (like Word, email) and lower –layer network services so that the network can understand an application's request and data sent from the network. This layer protocols helps software applications discuss their formatting , procedural, security, synchronization, and other requirements This layer is sixth layer of OSI model below the Application layer. This layer Protocols accept Application layer data and format information. The task of this layer is to serve as translator which it does by doing the compressing and encoding of graphics of the information received. It also understands a coded and compressed format in data received from other computers and manages data encryption and decryption Session: This layer coordinates and maintains communications between two nodes on the network. This layer's functions are to establishing and keeping alive the communications link, secure, synchronizing between the two nodes. This also determining communications cut off if so restart transmission and terminating communications. This layer services also set the terms of communication by deciding which node communicates first and how long a node can communicate. This layer monitors the identification of session participants, ensuring that only the authorized nodes can access the session. This layer accepts data from the Session layer and manages end-to-end delivery of data. This can ensure that the data is transferred from point A to point B constantly in the correct sequence, and without errors. This layer sees that the data is verified or understand by its receiver. These layers' protocols also handle flow control process of determine the suitable rate of transmission based on how fast the receiver can accept data. In this layer protocols take steps to ensure that data arrives exactly as it was sent. Such protocols are connection oriented, because they establish a connection with another node before they begin The primary function of this layer is to divide data receives from the Network layer into different frames that can then be transmitted by the Physical layer. A frame is an ordered package for moving raw data. It also needs sender and receiver network addresses, error checking and control information. The addresses tell the network where to deliver the frame, whereas the error checking and control information ensure that the frame arrives without any problems. The Error checking is skilled by a 4-byte FCS (frame check sequence) this purpose is to ensure that the data at destination exactly matches to issue from source. When the source node transmits the data, it performs an algorithm called a CRC (cyclic redundancy check). CRC takes the values of all of the earlier fields in the frame and generates a unique 4-byte number that is FCS. When the destination node receives the frame, its Data Link layer services order the FCS(frame check sequence) via the same CRC Cyclic Redundancy Check algorithm and ensure that the frame's fields match their original form. This Layer Protocols accept frames from the Data Link layer and generate signals as changes in voltage at the NIC. (Signals are made of electrical impulses that, when issued in a certain pattern, represent information.) When the network uses copper as its transmission medium, these signals are also issued over the wire as

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