Basics | Notion

📡 Core Concepts

API: Rules/interface for software communication.
Protocol: Standards for data exchange.
IP Address: Unique device ID. IPv4 = 32-bit, IPv6 = 128-bit, dual addressing supported.
Port: Identifies running app/service.
Socket = IP + Port: Unique communication endpoint.
Domain Name: Human-readable alias for IP (e.g., example.com).
DNS: Resolves domain name to IP via recursive queries (Root ➝ TLD ➝ Authoritative).

🔌 TCP/IP Stack (Internet Protocol Suite)

🏓 Layers

Layer	Purpose
Application	Handles data for processes/apps
Transport	End-to-end socket communication (TCP/UDP)
Network	Packet routing via IP
Hardware	Converts packets to/from network signals

🧳 Data flows downward at source (chunked and added with headers) and upward at destination (reconstruction).

🌐 TCP vs UDP

TCP: Connection-oriented, reliable, uses sequence numbers, checksums, and acknowledgments (ACKs). Ensures delivery with retransmissions.
UDP: Connectionless, no error checking or acknowledgments. Much faster, ideal for real-time streaming (video/audio).

🤝 TCP 3-Way Handshake

SYN – Client initiates connection with a TCP segment having SYN flag set (Seq=x).
SYN-ACK – Server replies with segment SYN & ACK set (Ack=x+1) (Seq=y).
ACK – Client sends segment (Ack=y+1) to confirm