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Difficulty: EasyEncapsulation and De-encapsulation

During the outbound encapsulation process on a host system, application data is passed down the protocol stack. At the Transport layer (Layer 4), a TCP header containing source and destination port numbers is attached to the data payload. Which Protocol Data Unit (PDU) is generated at this specific layer?

  1. SegmentAnswer
  2. B
    Packet
  3. C
    Frame
  4. D
    Bit stream

Answer

Segment
The correct answer is Segment. When data moves down to Layer 4 (Transport layer) during encapsulation, a header containing control information—such as TCP source/destination port numbers and sequence numbers—is added to the data payload, forming a Segment.

Step-by-Step Solution

1
Identify the OSI layer referenced in the scenario.
The scenario explicitly describes adding Transport layer headers (Layer 4) such as port numbers.
Different protocol layers produce specific Protocol Data Units (PDUs) during data encapsulation.
2
Map Layer 4 to its corresponding Protocol Data Unit term.
Layer 4 produces Segments (for TCP) or Datagrams (for UDP).
Encapsulation naming conventions designate Data at Layers 5-7, Segment at Layer 4, Packet at Layer 3, Frame at Layer 2, and Bits at Layer 1.

Key Concept

OSI Protocol Data Unit (PDU) Encapsulation Terminology
Estimated Time:45s
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Topics

Encapsulation and De-encapsulation

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