TCP vs UDP Behavior for A+

Concept 1

Required terms

TCP: Transmission Control Protocol; a connection-oriented transport protocol that provides sequencing, acknowledgments, and retransmission for reliable delivery. UDP: User Datagram Protocol; a connectionless transport protocol with minimal overhead, no built-in retransmission, used for short request/response or timing-sensitive traffic. TCP: Transmission Control Protocol; connection-oriented, reliable, sequencing and acknowledgment features. Recognition cue: web sessions, remote login, file transfer. Common confusion: "TCP always better". UDP: User Datagram Protocol; connectionless, minimal overhead, no retransmission guarantees. Recognition cue: DNS queries, DHCP exchanges, NTP. Common confusion: "UDP is just broken/unreliable".

Concept 2

How TCP vs UDP Behavior works

TCP establishes a session (handshake), tracks sequence numbers, and retransmits lost segments so data arrives complete and ordered. This makes it suitable for applications where correctness matters. UDP sends independent datagrams without establishing a session; it is useful where low latency or simplicity matters and the application tolerates or handles occasional loss.

Concept 3

Common confusion

- Misapplying a blanket rule that TCP is "slow" and UDP is "fast". The correct factor is the application's need for reliability vs overhead. - Expecting retransmission or ordering from UDP-based services; many UDP services are designed to tolerate loss. - Confusing transport behavior with port numbers: the same port number is not transport-agnostic; some services explicitly use TCP or UDP as their default.

Concept 4

Core 1 (220-1201) question cues

Given a scenario that needs reliable ordered data (remote desktop, file download), ask: which transport is appropriate and why? (Answer: TCP; needs sequencing and retransmission.); Given a quick request/response scenario (DNS lookup or DHCP exchange), ask: which transport and which ports are likely involved? (Answer: UDP; DNS 53, DHCP 67/68.); Given a mixed outcome, ask the student to justify the transport selection based on application needs rather than general performance statements.

Q1.An A+ support scenario describes this situation: Remote shell attempts: secure remote admin tools use TCP (SSH on 22). If a remote CLI fails to connect, think TCP. Which answer fits best?

Q2.For this A+ objective, the scenario says: Client cannot obtain IP: DHCP uses UDP (67/68). Time synchronization problems: NTP uses UDP (123). DNS resolution failures: DNS queries typically use UDP (53) for queries. What is the best match?

Q3.A user reports this support situation: Client cannot obtain IP: DHCP uses UDP (67/68). Time synchronization problems: NTP uses UDP (123). DNS resolution failures: DNS queries typically use UDP (53) for queries. Which option should the technician choose?