200-901 Network Fundamentals Practice Question
An application requires reliable, ordered delivery of data with flow control and retransmission of lost segments. Which transport layer protocol should the developer choose and what is a key characteristic of this protocol?
⚠ Common exam trap
The trap is the false pairing of UDP with TCP-like features (sequence numbers, handshakes) or the misconception that TCP has lower overhead — candidates must remember TCP trades overhead for reliability.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
TCP; it uses a three-way handshake for connection establishment
TCP is the correct transport protocol because it provides reliable, ordered delivery with flow control and retransmission of lost segments, and a defining characteristic is that it establishes connections via the three-way handshake (SYN, SYN-ACK, ACK). UDP provides none of these guarantees, and TCP actually has higher overhead than UDP, not lower.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
TCP; it uses a three-way handshake for connection establishment
Why this is correct
TCP's sequence numbers and acknowledgements guarantee ordered delivery, while windowing provides flow control and unacknowledged segments are retransmitted — exactly the reliability the application demands. The three-way handshake establishes the connection state these mechanisms depend on before any data flows.
- ✗
UDP; it provides ordered delivery through sequence numbers
Why it's wrong here
UDP is connectionless and provides no sequence numbers, acknowledgements or retransmission, so it cannot guarantee ordered delivery; ordering must be implemented in the application. UDP suits streaming, DNS and VoIP where low latency matters and occasional loss is tolerable, but it fails this reliability requirement.
- ✗
TCP; it has lower overhead than UDP
Why it's wrong here
TCP does satisfy reliability, ordering, flow control and retransmission, but its header, acknowledgements and connection state add overhead compared with UDP, so claiming lower overhead is factually wrong. TCP is correctly chosen for file transfer, HTTP and database sessions where guaranteed ordered delivery outweighs that overhead.
- ✗
UDP; it uses a three-way handshake for connection establishment
Why it's wrong here
UDP performs no handshake; the three-way SYN, SYN-ACK, ACK exchange establishes TCP connections. UDP simply transmits datagrams, so this description is wrong and the protocol cannot meet the reliability requirement. UDP is correct for DNS queries, DHCP and real-time media where connection setup overhead is unwanted.
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
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