What is the key difference between TCP and UDP in the Internet protocol suite with respect to connection semantics and service model?

Introduction / Context:
Applications choose between TCP and UDP based on their needs for reliability, ordering, flow control, and latency. Understanding the fundamental service models helps you select the right transport for web, streaming, gaming, or control applications.

Given Data / Assumptions:

• Transport protocols compared: TCP and UDP.
• We focus on connection semantics and service characteristics.
• No assumptions about specific applications beyond common usage patterns.

Concept / Approach:
TCP (Transmission Control Protocol) is connection-oriented: it establishes a logical connection (three-way handshake), provides reliable delivery (ACKs, retransmissions), ordered byte stream, and flow/congestion control. UDP (User Datagram Protocol) is connectionless and message-oriented (datagram): it sends independent packets without built-in reliability or ordering, minimizing overhead and latency.

Step-by-Step Solution:
Identify TCP features: connection setup, reliable, ordered stream, congestion control.Identify UDP features: no connection, no guaranteed delivery/order, simple header.Map to the option that states “UDP is a datagram service whereas TCP is a connection-oriented service.”

Verification / Alternative check:
Typical mappings: HTTP/HTTPS over TCP for reliable delivery; DNS queries commonly over UDP for speed (with TCP fallback for truncation); live media sometimes uses UDP-based protocols to avoid retransmission delays.

Why Other Options Are Wrong:
UDP connection-oriented and TCP datagram: Reversed and incorrect.

TCP Internet vs UDP ATM: UDP is also an Internet transport; ATM is a different technology stack.

All/None of the above: Do not fit the accurate characterization.

Common Pitfalls:
Assuming UDP is “unreliable” in all senses; reliability can be built at the application layer. Conversely, assuming TCP is always best; latency-sensitive apps may prefer UDP.

Final Answer:
UDP is a datagram service whereas TCP is a connection-oriented service