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Protocol
A set of rules that devices follow. A set of processes to follow INVOLVES MORE THAN 1 PERSON, IT CANNOT BE YOURSELF
Internet structure
The internet is a network of networks. When you send data, it hops through many routers and networks to reach the destination — not directly.
End system (host)
A device that connects to the internet and uses network apps, like your phone, laptop, or a web server.
Application layer
Where apps like web browsers and email live — it’s what the user interacts with.
Transport layer
Handles reliable delivery of messages between apps (like making sure your message arrives complete and in order).
Network layer
Decides the best path for your data to travel across networks — it deals with IP addresses.
Link layer
Deals with communication between devices on the same network, like your PC and your router.
Physical layer
All the hardware stuff — wires, Wi-Fi signals, anything that physically moves bits.
Encapsulation
As data goes down the layers, each layer adds its own header to the message. When it’s received, the layers remove the headers in reverse order.
Packet sniffer
A tool that captures and lets you see network traffic. Useful for debugging, but can be misused to steal passwords or spy on users.
HTTP
The protocol used by web browsers to request and receive web pages.
SMTP
The protocol used to send emails between servers.
HTTP request structure
Includes method (GET/POST), URL, headers, and maybe a body. It’s a way to ask a server for something.
Caching (in HTTP and DNS)
Temporary storage of recent data so future requests are faster. Browsers, DNS servers, and even your OS use it.
HTTP vs SMTP
HTTP pulls data (client asks, server sends), while SMTP pushes it (client sends data to server). Also, SMTP stores messages; HTTP doesn’t.
Socket
A combo of IP address and port number that lets apps send/receive data. Think of it as the app’s "address" on the internet.
DNS (Domain Name System)
Translates easy-to-remember names (like google.com) into IP addresses. Without it, you’d have to remember numbers.
Steps of DNS query (e.g. to visit www.utrgv.edu)
Browser checks cache → Asks OS → Asks DNS resolver → May ask root server → TLD server → Authoritative server → Gets IP → Connects.
Client
A device/app that makes requests (like your browser).
Server
A device/app that responds to requests (like a website's backend).
Client-server model
Client initiates connection, server waits for requests. Server usually has more resources and is always online.
P2P (Peer-to-peer)
Devices talk directly to each other and share resources (like BitTorrent). No need for a central server, more scalable.