Jagannath University — Department of CSE — MSc Admission: 2019প্রশ্ন ও সমাধান

TCP is a connection-oriented, reliable transport protocol; UDP is connectionless and unreliable but much faster — the choice between them depends on whether an application needs guaranteed delivery or low latency.

Aspect	TCP	UDP
Connection	Connection-oriented (3-way handshake)	Connectionless
Reliability	Guaranteed delivery, retransmits lost packets	Best-effort, no retransmission
Ordering	Packets delivered in order	No ordering guarantee
Speed/overhead	Slower, higher overhead (headers, ACKs)	Faster, minimal overhead
Flow/congestion control	Yes	No
Header size	20 bytes (minimum)	8 bytes
Typical use	Web (HTTP/S), email, file transfer	DNS, video/voice streaming, online gaming

sequenceDiagram
    participant C as Client
    participant S as Server
    C->>S: SYN
    S->>C: SYN-ACK
    C->>S: ACK (connection established)
    C->>S: Data (TCP - acknowledged, ordered)
    Note over C,S: UDP: Client simply sends datagrams,<br/>no handshake, no acknowledgement

• TCP trades speed for reliability via handshaking, sequence numbers, acknowledgements, and retransmission — essential when data loss/corruption is unacceptable (e.g. a downloaded file).
• UDP skips all of that overhead, favouring speed — ideal when occasional lost packets are tolerable (a dropped video frame is barely noticed, but a stalled call while TCP retransmits is worse).

Exam takeaway: TCP = reliable but slower (web, email, files); UDP = fast but unreliable (DNS, streaming, gaming) — pick based on whether the application can tolerate loss in exchange for speed.