Within the TCP/IP suite, which description correctly characterizes Transmission Control Protocol (TCP)?

Introduction:
Transmission Control Protocol (TCP) is a foundational transport protocol of the Internet. Understanding its reliability, connection semantics, and OSI placement is essential for networking and systems exams.

Given Data / Assumptions:

• OSI reference layers: Physical, Data Link, Network, Transport, Session, Presentation, Application.
• TCP is part of the transport layer in the TCP/IP model (mapped to OSI Transport).
• We compare connection orientation and reliability features.

Concept / Approach:
TCP establishes a virtual circuit via a 3-way handshake, ensures ordered delivery, provides retransmissions, flow control (windowing), and congestion control. It is therefore connection oriented and reliable. UDP, in contrast, is connectionless and unreliable.

Step-by-Step Solution:

Verification / Alternative check:
Use the mnemonic: TCP = handshake + ACKs + sliding window + congestion control; UDP = minimal, best-effort datagrams.

Why Other Options Are Wrong:

• Data Link layer: incorrect layer; TCP is Transport.
• Connection oriented and unreliable: contradicts TCP’s reliability features.
• Connectionless and unreliable: describes UDP-like behavior.
• Connectionless and reliable: uncommon pairing; not TCP.

Common Pitfalls:
Confusing OSI vs TCP/IP models; assuming “connection” equals “physical circuit” rather than a logical state machine.

Final Answer:
TCP is connection oriented and reliable.