Transport Layer Protocols Questions

Comprehensive understanding of transport layer protocols, primarily Transmission Control Protocol (TCP) and User Datagram Protocol (UDP), and related protocols used for diagnostics such as Internet Control Message Protocol (ICMP). Candidates should be able to explain TCP as a connection oriented, reliable, ordered, and flow controlled protocol including the three way handshake for connection establishment, the four step connection teardown, retransmission and timeout behavior, and high level congestion control and flow control mechanisms. Describe TCP header structure and key fields used for reliability and ordering. Explain UDP as a connectionless, best effort, lower latency protocol, its datagram model, simple header structure, and trade offs for reliability and ordering. Give real world use cases and justify protocol choice, for example reliable file transfer and web traffic versus low latency streaming, real time voice, and many DNS queries. Discuss port numbers and common service ports such as HTTP port 80, HTTPS port 443, DNS port 53, SSH port 22, and SMTP port 25, and how sockets and ports map to endpoints. Cover practical topics such as when UDP may fall back to TCP, how fragmentation and packet loss affect each protocol, and the role of ICMP for network diagnostics and error reporting.