OSI Layer 4 mapping: which transport protocol underlies a Telnet connection?

Introduction / Context:
Telnet provides remote terminal access and requires a reliable byte stream to carry interactive text. Selecting the correct Layer-4 protocol helps ensure ordered, error-checked delivery suited for terminal sessions.

Given Data / Assumptions:

• Telnet is a classic application-layer protocol (port 23).
• It predates SSH and relies on cleartext transport.
• Transport requirements: ordered, reliable delivery.

Concept / Approach:
Only TCP provides reliable, connection-oriented delivery in the traditional TCP/IP stack. UDP is connectionless and does not guarantee order or delivery, which is not ideal for interactive remote shells like Telnet.

Step-by-Step Solution:

Verification / Alternative check:
Run a port scan or consult IANA port assignments: Telnet is assigned to TCP port 23. UDP 23 is not commonly used.

Why Other Options Are Wrong:
IP: Network layer, not transport.
TCP/IP: A stack name, not a single protocol.
UDP: No reliability/ordering guarantees; unsuitable for standard Telnet.

Common Pitfalls:
Thinking “TCP/IP” is an option equivalent to TCP. It is not; always select the precise layer protocol.

Final Answer:
TCP