Computer Networking Review: OSI, TCP/UDP, HTTP, DNS, CDN, and WebSocket

Networking fundamentals matter for frontend, backend, and cloud engineering.

OSI and TCP/IP

The OSI model has seven layers:

Physical
Data Link
Network
Transport
Session
Presentation
Application

TCP/IP is often simplified into four layers: network interface, internet, transport, and application.

TCP and UDP

TCP is connection-oriented and reliable. It uses a three-way handshake and a four-way teardown. It is suitable for file transfer, web requests, and database connections.

UDP is connectionless and lightweight. It does not guarantee delivery. It is suitable for real-time audio/video, games, and DNS.

HTTP and HTTPS

HTTP is plaintext. HTTPS adds TLS encryption.

Common methods:

GET: read
POST: create
PUT: full update
PATCH: partial update
DELETE: delete

Common status codes:

200: success
301/302: redirect
400: bad request
401: unauthenticated
403: forbidden
404: not found
500: server error

DNS and CDN

DNS resolves domain names into IP addresses. CDN caches static assets at edge locations closer to users.

WebSocket

WebSocket is a long-lived connection protocol. It is useful for chat, notifications, and collaborative editing.

HTTP/2

HTTP/2 improves over HTTP/1.1 with multiplexing, header compression, and more efficient connection reuse.

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