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Difficulty: MediumOSI Model Layers and Functions

A network host receives an incoming web session over an encrypted HTTPS connection. Arrange the following decapsulation steps in the correct order in which they are processed by the receiving system, starting from the lowest OSI layer (Data Link) up to the Presentation layer.

  1. 1The Network Interface Card verifies the Frame Check Sequence (FCS) and strips the Ethernet header.
  2. 2The operating system examines the destination IP address in the packet header to ensure local delivery.
  3. 3The transport stack uses the TCP header port numbers to reassemble segments into a continuous stream for the socket.
  4. 4The TLS subsystem decrypts the payload into cleartext data suitable for rendering.

Answer

The decapsulation sequence proceeds from Layer 2 to Layer 6: Ethernet frame check and header stripping (Data Link), IP address processing (Network), TCP port routing and segment reassembly (Transport), and TLS payload decryption (Presentation).
The correct order follows the OSI model bottom-up decapsulation path: Layer 2 Data Link (Ethernet FCS/header), Layer 3 Network (IP address header), Layer 4 Transport (TCP port/reassembly), and Layer 6 Presentation (TLS decryption).

Step-by-Step Solution

1
Identify Data Link Layer (Layer 2) functions.
The frame checksum (FCS) verification and Ethernet header removal happen first upon arrival at the network interface.
Lower layer encapsulation framing must be validated and removed before higher layer protocol headers can be accessed.
2
Identify Network Layer (Layer 3) functions.
The IP header is evaluated to confirm the destination network address matches the receiving host.
Network layer headers contain logical addressing required to route the packet to the correct destination host.
3
Identify Transport Layer (Layer 4) functions.
TCP port numbers are evaluated and segments are reassembled.
Transport layer mechanisms manage connection streams and multiplexing to specific service ports.
4
Identify Presentation Layer (Layer 6) functions.
TLS decryption transforms the raw encrypted payload into application-readable data.
Encryption/decryption, data compression, and character encoding/formatting are responsibilities of Layer 6.

Key Concept

OSI Layer Decapsulation Order and Layer Functions
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Topics

OSI Model Layers and Functions

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