Answer: Only I and III.

## Explanation Let's analyze each statement about TCP protocol characteristics: **I. Confirms messages that have already been delivered.** - **CORRECT** TCP provides reliable delivery through acknowledgment mechanisms. When a receiver gets a packet, it sends an ACK (acknowledgment) back to the sender, confirming successful delivery. **II. It is optional for it to perform congestion control.** - **INCORRECT** Congestion control is a fundamental, mandatory feature of TCP, not optional. TCP uses algorithms like slow start, congestion avoidance, fast retransmit, and fast recovery to manage network congestion. **III. Delivers messages in order.** - **CORRECT** TCP provides in-order delivery of data. Even if packets arrive out of order (which can happen in IP networks), TCP reorders them before delivering to the application layer. **IV. Is half-duplex.** - **INCORRECT** TCP is **full-duplex**, not half-duplex. Full-duplex means data can flow in both directions simultaneously. TCP connections allow bidirectional communication with separate sequence numbers and acknowledgments for each direction. **Correct statements:** I and III only **Why other options are incorrect:** - **Option B (II and IV)**: Both statements are incorrect - **Option C (I, II, III)**: Statement II is incorrect - **Option D (II, III, IV)**: Statements II and IV are incorrect - **Option E (all)**: Statements II and IV are incorrect

Author: Danyel Barboza