Within the OSI/TCP-IP model mapping, what is the core responsibility of the transport layer (transport protocol)?

Introduction / Context:
The transport layer sits between application protocols and the network layer. It segments application data, assigns ports, and may provide reliability, ordering, and congestion/flow control. Understanding its role clarifies how TCP and UDP differ and how applications map to endpoints.

Given Data / Assumptions:

• We model communications using the OSI reference and the TCP/IP suite.
• Transport protocols include TCP (reliable, connection-oriented) and UDP (connectionless, minimal services).
• We want the definition that best captures end-to-end logical connections and reliability.

Concept / Approach:
The transport layer builds logical associations between processes (ports) on hosts, coordinating segmentation/reassembly. TCP provides reliable, ordered delivery, flow control, and congestion control. UDP provides multiplexing and optional checksum without connection state. Presentation (data representation) and session (dialog management) are higher-layer concerns; adapter control is lower-layer (data link/physical).

Step-by-Step Solution:

Verification / Alternative check:
Examine TCP headers (ports, sequence, acknowledgment numbers) and behavior (retransmissions, sliding windows). This confirms the transport layer’s reliability role, separate from routing (network) and framing (data link).

Why Other Options Are Wrong:

• Presentation/session responsibilities do not belong to the transport layer.
• Adapter management belongs to the data link/physical layers and drivers.
• ‘‘None of the above’’ is incorrect because one option correctly describes transport.

Common Pitfalls:
Confusing TCP (transport) with IP (network) or assuming UDP provides reliability; reliability on UDP must be implemented by the application.

Final Answer:
Establishes logical end-to-end connections and supports reliable data transfer between communicating computers