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Difficulty: EasyEncapsulation and De-encapsulation

A workstation application generates data to be sent across a network. In what order are the protocol data units (PDUs) created during the outbound encapsulation process, from the first unit formed at the top of the stack to the final unit prepared for network media transmission?

  1. 1Data (Application Payload)
  2. 2Segment / Datagram (Transport Layer PDU)
  3. 3Packet (Network Layer PDU)
  4. 4Frame (Data Link Layer PDU)

Answer

The correct order of outbound PDU encapsulation from top to bottom is: Data, Segment, Packet, and Frame.
Outbound encapsulation flows from the top layer down through the OSI stack: Data (Layers 5-7) is encapsulated into a Segment at Layer 4, which is encapsulated into a Packet at Layer 3, and finally wrapped into a Frame at Layer 2 before physical transmission.

Step-by-Step Solution

1
Identify the initial top-layer data payload
Raw Data is produced at the Application layer.
Encapsulation moves downward through the protocol stack starting from application software.
2
Attach Layer 4 headers
Data becomes a Segment (or UDP Datagram).
The Transport layer adds port numbers and sequence controls to the application data.
3
Attach Layer 3 headers
The Segment becomes a Packet.
The Network layer encapsulates the segment with logical IP source and destination addresses.
4
Attach Layer 2 headers and trailers
The Packet becomes a Frame.
The Data Link layer wraps the packet in hardware MAC address headers and a Frame Check Sequence (FCS) trailer prior to bit transmission on the physical media.

Key Concept

Outbound Encapsulation Sequence and Protocol Data Unit (PDU) Terminology
Estimated Time:45s
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Topics

Encapsulation and De-encapsulation

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