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Difficulty: EasyEncapsulation and De-encapsulation

A host computer initiates a file transfer and passes data down the OSI model stack for network transmission. Which of the following sequences correctly lists the Protocol Data Units (PDUs) generated during this outbound encapsulation process in order from the highest layer to the lowest layer?

  1. Data, Segment, Packet, Frame, BitsAnswer
  2. B
    Data, Packet, Segment, Frame, Bits
  3. C
    Bits, Frame, Packet, Segment, Data
  4. D
    Data, Segment, Frame, Packet, Bits

Answer

The correct sequence of Protocol Data Units (PDUs) during outbound encapsulation from highest layer to lowest layer is Data, Segment, Packet, Frame, and Bits.
Outbound encapsulation processes data top-down through the protocol stack. The Application, Presentation, and Session layers manage Data. The Transport layer encapsulates this into Segments (or UDP datagrams). The Network layer encapsulates segments into Packets with logical IP addresses. The Data Link layer encapsulates packets into Frames with physical MAC addresses. Finally, the Physical layer converts frames into Bits for transmission over the network medium.

Step-by-Step Solution

1
Determine the direction of data flow from the scenario.
The host is sending data, meaning traffic moves outbound (top-down) from upper applications down to the physical medium.
Outbound traversal requires adding headers sequentially from Layer 7 to Layer 1.
2
Match each OSI layer to its designated Protocol Data Unit (PDU).
Layers 5-7 handle Data, Layer 4 creates Segments, Layer 3 creates Packets, Layer 2 creates Frames, and Layer 1 transmits Bits.
Each layer encapsulates data received from the layer above by appending its own header/trailer.
3
Arrange the PDUs in top-down sequence.
Data → Segment → Packet → Frame → Bits.
This order reflects the exact encapsulation workflow of an originating host stack.

Key Concept

OSI Layer Encapsulation Order and PDU Terminology
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Topics

Encapsulation and De-encapsulation

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