Transport Layer

• TCP (Transmission Control Protocol): connection-oriented, reliable (guarantees delivery, order, error-checking via acknowledgments/retransmission), includes flow control and congestion control — slower but reliable (e.g., web browsing, file transfer)
• UDP (User Datagram Protocol): connectionless, unreliable (no delivery guarantee, no retransmission) — faster, lower overhead (e.g., video streaming, DNS, online gaming)
• Multiplexing at this layer: port numbers allow multiple applications to share one IP address
• Congestion control: mechanisms (e.g., TCP's slow start, congestion avoidance) that reduce sending rate when network congestion is detected

MCQ Trap

• TCP is connection-oriented and reliable; UDP is connectionless and unreliable but faster — the single most frequently tested networking distinction.