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Difficulty: MediumOSI Model Layers and Functions

A host system prepares to send data over a network connection using the standard OSI protocol stack. Place the following processing steps in the correct order, starting from higher-layer data preparation down to physical transmission over the wire.

  1. 1Data formatting, character encoding, and encryption are applied to prepare the application payload.
  2. 2Source and destination port numbers are added to segment the data for process-to-process communication.
  3. 3Logical IP addressing and header information are appended to route the packet across network boundaries.
  4. 4Physical MAC addresses and a Frame Check Sequence (FCS) trailer are added to form data frames.
  5. 5The binary data stream is encoded into electrical signals or light pulses for medium propagation.

Answer

The correct encapsulation order flows top-down: Presentation Layer formatting/encryption, Transport Layer port segmenting, Network Layer IP packet routing, Data Link Layer MAC/FCS framing, and Physical Layer bit transmission.
During outbound transmission, data undergoes top-down encapsulation through the OSI reference model: Layer 6 (Presentation) formats and encrypts data, Layer 4 (Transport) appends port headers, Layer 3 (Network) appends IP headers, Layer 2 (Data Link) appends MAC headers and FCS trailers, and Layer 1 (Physical) converts bits into signals on the physical wire.

Step-by-Step Solution

1
Identify higher-layer data processing (Layer 6)
Formatting, encoding, and encryption occur at the Presentation Layer first.
Data must be properly formatted before transport sessions and encapsulation begin.
2
Identify transport segment processing (Layer 4)
Port numbers are attached to create segments.
Transport Layer handles end-to-end communication pathways and service port identification.
3
Identify logical addressing encapsulation (Layer 3)
Logical IP headers are attached to form packets.
Network Layer adds IP routing information for cross-network path selection.
4
Identify local framing and error detection (Layer 2)
MAC addresses and FCS trailers are added to create frames.
Data Link Layer formats data for transmission across the physical local link.
5
Identify physical signal conversion (Layer 1)
Binary bits are converted to physical signals.
Physical Layer handles the actual hardware signal transmission.

Key Concept

OSI Model Encapsulation Sequence
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Topics

OSI Model Layers and Functions

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