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

Question

Solve this multiple-choice question and choose the correct option.

Accepted Answer

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: Map Telnet's port: 23/TCP.Match needs (reliability, order) to TCP features (sequence numbers, ACKs, retransmission).Confirm IP alone is Layer-3 and “TCP/IP” is a suite label, not a Layer-4 protocol. 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

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

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