Basic CS-Networks [3i Infotech Placement]: Sample Questions 36 - 36 of 90

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Question 36


Describe in Detail


Define OSI model and their functions, what popular protocol fit in OSI model.


OSI Model with All Layers

OSI model and their functions

Physical layer:

  • The lowest layer of the OSI model transmits and receive unstructured raw bit stream over a physical medium.

    It provides:

    • Data encoding:
      • Modifies digital signal pattern (of 1s and 0s) to accommodate the characteristics of the analogue physical medium
      • Aids in bit and frame synchronization
    • Transmission technique:
      • Determines whether the encoded bits will be transmitted by baseband or broadband signalling.

Data Link layer:

  • Provides error free transfer of data frames between notes over physical layer, allowing layers above to assume error free transmission over the link (although in reality that is not the case) .
  • The data link layer provides:
    • Link establishment and termination:
      • Establishes and terminates the logical link between two nodes.
    • Frame traffic control:
      • Communicates the transmitting node to “back-off” when no frame buffers are available (to store the incoming frames) .
    • Frame sequencing:
      • Transmits and receives frames sequentially.
    • Media access management:
      • Determines the access rights to use the physical medium.

Network later:

  • Controls the operation of the subnet.
  • Decides the physical path the based on network conditions, priority of service, and other factors.

    It provides:

    • Routing:
      • Routes frames among networks.
    • Logical-physical address mapping:
      • Translates logical addresses, or names, into physical addresses.
    • Subnet usage accounting:
      • Provides accounting functions keeping track of frames forwarded by subnet intermediate system.

Transport Layer:

  • Ensures messages are delivered error free
  • Messages are delivered in sequence
  • Allows messages to be delivered with no losses or duplications.
  • Relieves the higher layer protocols from above concerns during transfer of data.

    It provides:

    • Message segmentation:
      • Accepts a message from the layer above it and passes the smaller units down to the network layer.
    • Message acknowledgment:
      • Provides reliable end-to-end message delivery with acknowledgments.
    • Message traffic control:
      • Communicates transmitting station to “back-off” when no message buffers are available.
    • Session multiplexing:
      • Multiplexes several message streams, or sessions onto one logical link keeping track of messages belonging to sessions.

Session Layer:

  • Allows session establishment between processes running on different stations.

    It provides:

    • Session establishment, maintenance and termination:
      • Allows two application processes on different machines to establish, use and terminate a connection, called a session.
    • Session support:
      • Allow processes to communicate over the network- provides security, name recognition, logging.

Presentation layer:

  • Formats the data presented to the application layer.
  • Viewed as the translator for the network.

    It provides:

    • Character code translation:
      • For example, ASCII to EBCDIC.
    • Data conversion:
      • Bit order, CR-CR/LF, integer-floating point, and so on.
    • Data compression:
      • Reduces the number of bits to be transmitted on the network.
    • Data encryption:
      • Encrypt data for security purposes. For example, password encryption.

Application layer:

  • Provides methods and applications to users and processes to access network services.

    It provides:

    • Resource sharing and device redirection
    • Remote file access
    • Remote printer access
    • Inter-process communication

Popular protocol in OSI model:

  • TCP:
    • Transmission control protocol is one of the main internet protocols.
    • Complements the Internet Protocol.
    • Is a transport layer protocol in the OSI layer
    • Used to create a connection between remote computers by transporting.
    • Ensures the delivery of messages over supporting networks and the Internet.
    • Creates active connection between the source and destination node.
  • UDP:
    • User datagram protocol
    • Part of the internet protocol used by programs running on different computers on a network.
    • Can send short messages called datagrams- but unreliable, connectionless protocol.
    • Widely used in video conferencing and real time computer games- some data like frames can be dropped.
  • ICMP:
    • Internet control message protocol is an error reporting protocol for network devices
    • Provides error messages to the source IP when network problems prevent delivery of IP packets.
    • Created to communicate errors in an IP datagram or for diagnostic routing purposes.
    • Errors are reported to the originating datagram՚s source IP address.
  • IP:
    • Internet protocol is the method or protocol to send data across computers on internet.
    • All hosts or network nodes must be configured with the TCP/IP suite.
    • Communication occurs when a host sends a data packet to another host by addressing its IP address.
  • Ethernet:
    • Widely installed local area network technology.
    • Link layer protocol in TCP/IP stack can format data for transmission to other network devices
    • Component of Ethernet network:
  1. Ethernet cable
  2. Ethernet hub
  3. Crossover cable
  4. Router
Component of Ethernet Network

Developed by: