OSI layer for segmentation: At which OSI layer is a continuous data stream segmented into smaller transport units for delivery across the network?

Introduction / Context:
Large application data streams are broken into manageable pieces for reliable delivery. Identifying the OSI layer responsible for segmentation helps map functions like flow control, sequencing, and reassembly to the proper protocol stack layer.

Given Data / Assumptions:

• Segmentation refers to dividing the byte stream into segments (e.g., TCP).
• Layer responsibilities follow the OSI model.
• Reliable, ordered delivery is typically provided at the transport layer.

Concept / Approach:

The Transport layer (Layer 4) handles segmentation, sequencing, acknowledgment, and reassembly at the destination. TCP is the canonical example. Lower layers forward packets/frames; higher layers provide application semantics.

Step-by-Step Solution:

Verification / Alternative check:

Packet analyzers show TCP sequence numbers and segment sizes—clear evidence of Layer 4 segmentation and reassembly behavior.

Why Other Options Are Wrong:

Physical (A) transmits bits; Data Link (B) frames; Network (C) handles logical addressing and routing, not segmentation of application data.

Common Pitfalls:

Confusing fragmentation (Network layer, IP) with segmentation (Transport layer).

Final Answer:

Transport