Basic CS [3i Infotech Placement]: Sample Questions 186 - 186 of 243

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Question 186

Basic CS

Describe in Detail


What is Protocol Data Unit?


  • Protocol Data Unit is an open system interconnection term used in telecommunications
  • Refers to a group of information added or removed by a layer of the OSI model.
  • Represents a unit of data specified in the protocol of a given layer- consisting of protocol control information and user data.
  • Term specifically related to the initial four layers of the OSI model.
  • DSAP (Destination Service Access Point) , SSAP (Source Service Access Point) are addresses used by the LLC (Logical Link Control) to identify the protocol stacks on the receiving and sending machines generating and using the data.

PDU for each layer of the OSI model is listed below:

  • Physical layer
    • Raw bits (1s or 0s) transmitted physically via the hardware
  • Data Link layer
    • A frame
  • Network layer
    • A packet that contains the source and destination address
  • Transport layer
    • A segment that includes a TCP header and data
  • Session layer
    • The data passed to the network connection
  • Presentation layer
    • The data formatted for presentation
  • Application layer
    • The data received or transmitted by a software application

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