Computer_Network

How SYN, SYN-ACK, and ACK establish TCP state, synchronize initial sequence numbers, negotiate options, and protect against stale connection attempts.

TCP's independent half-close semantics, FIN/ACK exchange, FIN_WAIT/CLOSE_WAIT/LAST_ACK/TIME_WAIT states, and why termination is often illustrated with four segments.

How TCP's receiver-advertised window prevents a fast sender from overrunning the receiver, including sliding windows, zero windows, and window scaling.

TCP as a connection-oriented reliable byte-stream transport: sequencing, acknowledgements, retransmission, checksums, flow control, congestion control, and comparison with UDP.

TCP keepalive probes for detecting long-idle dead peers, and why application-level health checks often remain necessary in distributed systems.

What CLOSE_WAIT means, why it is a local application state after receiving FIN, and how persistent CLOSE_WAIT growth points to socket-lifecycle bugs.

TCP congestion windows, slow start, congestion avoidance, fast recovery, loss/ECN signals, and the distinction between classic Reno-style explanations and modern algorithms such as CUBIC and BBR.

HTTP/1.0, HTTP/1.1, HTTP/2, and HTTP/3: persistent connections, framing, multiplexing, header compression, TCP head-of-line blocking, and QUIC.

WebSocket's full-duplex message channel, HTTP/1.1 upgrade handshake, framing, masking, ping/pong, and comparison with polling, SSE, and ordinary HTTP.

A practical guide to HTTP 1xx-5xx status classes and the most important codes for APIs, caching, redirects, authentication, conflicts, rate limiting, and gateways.

How CDNs cache and serve content near users, use DNS/anycast steering, fill from origins, invalidate content, and trade freshness for latency and origin load.

DNS hierarchy, recursive resolvers, authoritative servers, A/AAAA/CNAME records, caching/TTL, DNS security, encrypted DNS, and traffic steering.