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Difficulty: Very hardOSI Model Layers and Functions

A systems engineer is auditing an enterprise application stack protocol to verify proper layer encapsulation and responsibility delegation according to the OSI model. The protocol performs syntax transformation, data payload reduction, session checkpointing, and segment reassembly. Which of the following functions operate strictly within the Presentation Layer (Layer 6) of the OSI model? (Select TWO.)

  1. Translating application data between ASCII and EBCDIC character encodingsAnswer
  2. Compressing application payload data prior to forwarding it down the protocol stackAnswer
  3. C
    Establishing and managing full-duplex dialogue control checkpoints between communicating endpoints
  4. D
    Negotiating sliding window sizes and port parameters to prevent buffer overrun

Answer

The functions operating strictly at the Presentation Layer (Layer 6) are character encoding translation (such as ASCII to EBCDIC) and data payload compression.
The Presentation Layer (Layer 6) acts as the data translator for the network. It handles syntax formatting, character encoding conversions (e.g., ASCII to EBCDIC), data compression, and encryption/decryption so that applications running on heterogeneous operating systems can interpret shared data.

Step-by-Step Solution

1
Identify the core responsibilities of Layer 6 (Presentation Layer) of the OSI model.
Layer 6 is responsible for data format translation, syntax conversion, encryption/decryption, and data compression.
This establishes the scope of Layer 6 independent of adjacent layers.
2
Evaluate character encoding translation against OSI layer definitions.
Converting between ASCII and EBCDIC transforms how syntax is represented without managing session dialogues or transport segments, matching Layer 6.
Character set conversion ensures disparate systems can interpret data structures.
3
Evaluate payload compression against OSI layer definitions.
Data compression manipulates the representation format of the payload, which is an explicit Presentation Layer service.
Compression occurs before data is handed off to Session/Transport layers.
4
Differentiate incorrectly categorized options.
Dialogue control checkpoints belong to Layer 5 (Session Layer), while sliding window flow control and port management belong to Layer 4 (Transport Layer).
Isolating Layer 5 and Layer 4 operations confirms that only character translation and compression belong to Layer 6.

Key Concept

OSI Presentation Layer (Layer 6) Services and Boundary Differentiation
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Topics

OSI Model Layers and Functions

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