Which transport-layer protocol is connectionless and provides best-effort delivery without built-in reliability?

Introduction / Context:
Transport-layer protocols provide end-to-end communication services. Some are connection-oriented with sequencing and retransmissions; others are connectionless with minimal overhead, favoring latency over reliability.

Given Data / Assumptions:

• We compare common protocols used in Internet stacks.
• Focus: whether the transport is connection-oriented or connectionless.

Concept / Approach:
UDP (User Datagram Protocol) is connectionless and provides best-effort delivery—no session setup, no guaranteed ordering, and no retransmission by the protocol itself. TCP, by contrast, is connection-oriented with reliability features. NVT and FTP are not transport protocols (application concepts/protocols).

Step-by-Step Solution:

Verification / Alternative check:
Refer to IETF standards: UDP is defined with minimal header fields (ports, length, checksum), and lacks sequence numbers and ACKs. TCP includes sequence/ack numbers and a three-way handshake.

Why Other Options Are Wrong:

• NVT: Network Virtual Terminal (a TELNET concept), not transport.
• FTP: Application-layer file transfer protocol.
• TCP: Connection-oriented, not connectionless.
• None: incorrect because UDP is explicitly connectionless.

Common Pitfalls:
Equating “connectionless” with “unreliable in all senses”; applications can add reliability on top of UDP if needed; also confusing IP (network layer) with UDP (transport layer).

Final Answer:
UDP