TCS Papers: Sample Questions 312 - 312 of 502

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Question number: 312

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Describe in Detail

List the layers of OSI


  • OSI model passes control from one layer to the next.

  • OSI model divides inter-networking into vertical stack with 7 layers:

    • Physical

      • Layer 1 conveys the bit stream - electrical impulse, light or radio signal — through the network at the electrical and mechanical level.

      • Provides hardware for sending and receiving data on a carrier, including defining cables, cards, and physical aspects.

      • Fast Ethernet, RS232, and ATM are protocols with physical layer components.

    • Data link

      • Layer 2 encodes data packets and decodes them into bits.

      • Furnishes transmission protocol knowledge and management and handles errors in the physical layer, flow control and frame synchronization.

      • The data link layer is divided into two sub layers: The Media Access Control (MAC) layer and the Logical Link Control (LLC) layer.

        • MAC sub layer controls network access to the data and permission to transmit it.

        • The LLC layer controls frame synchronization, flow control and error checking.

    • Network

      • Layer 3 provides switching and routing technologies, creating logical paths, known as virtual circuits, for transmitting data from node to node.

      • This functions handles routing and forwarding, as well as addressing, internetworking, error handling, congestion control and packet sequencing.

    • Transport

      • Layer 4, provides data transparent between end systems, or hosts, and is responsible for end-to-end error recovery and flow control.

      • Ensures complete data transfer.

    • Session

      • This layer establishes, manages and terminates connections between applications.

      • It sets up, coordinates, and terminates conversations, exchanges, and dialogues between the applications at each end.

      • Deals with session and does connection coordination.

    • Presentation

      • Provides independence from differences in data representation by translating from application to network format, and vice versa.

      • Transform data into the form that the application layer can accept.

      • Formats and encrypts data, providing freedom from compatibility problems.

      • Also called the syntax layer.

    • Application

      • Final highest layer which supports application and end-user processes.

      • Identifies communication partners, quality of service, user authentication and privacy issues, and constraints on data syntax.

      • This layer is application-specific- provides services for file transfers, e-mail, and other network software services.

      • Tiered application architectures like Telnet and FTP are part of this layer.

Image of the Layers of OSI

Image of the Layers of OSI

Given the image is define the 7 Layers of Open System Interconnection (OSI)