The vocabulary you need before any of the layered models make sense.
Protocols aren't invented by a single company — they're standardized, often region-by-region and globally, by bodies like the Internet Society, with the actual technical specifications published as RFCs (Request For Comments) through the RFC Editor. An RFC is essentially the "spec document" engineers refer back to when implementing a protocol correctly.
Client–Server model
The dominant pattern for how applications talk over a network:
Client request → Server
Client ← response Server
Client — initiates the request (your browser, your phone app).
Server — a machine that's always listening, waiting to respond to requests (identified by an IP address).
Casting modes: Unicast, Broadcast, Multicast
How data is addressed and distributed across the network determines its casting mode, operating at both Layer 2 (MAC) and Layer 3 (IP):
Circuit Switching vs Packet Switching
The two fundamental paradigms of moving data through a network mesh:
Direct Comparison
| Metric / Feature | Circuit Switching | Packet Switching |
|---|---|---|
| Resource Reservation | Dedicated path reserved upfront | Dynamic sharing on demand |
| Congestion / Queuing | None (Guaranteed bandwidth) | Yes (Packets wait in router queues) |
| Setup Delay | High (Requires signaling handshake) | None (Immediate transmission) |
| Link Efficiency | Low (Wasted during silence/idle) | High (Bursty traffic multiplexed) |
| Failure Resilience | Low (If a link cuts, the call drops) | High (Packets routed dynamically around faults) |
| Primary Use Case | Landline telephony (PSTN), GSM voice | The Internet, LANs, WANs |
IP Addresses
Every server you talk to is identified by an IP address, even though you usually type a domain name instead (DNS bridges that gap — covered later).
ISPs and the chain to your device
Your ISP (Internet Service Provider — e.g. Airtel, Jio, Comcast) is the company that actually connects your home or office to the wider internet.
The ISP gives you a modem/router, which is assigned a global (public) IP address — visible to the rest of the internet.
Inside your home, the router connects to internal devices (laptop, phone, smart TV).
Each of those internal devices gets a private/local IP address, automatically handed out by DHCP (Dynamic Host Configuration Protocol).
Ports
Ports are 16-bit numbers → range from 0 to 2¹⁶−1, i.e. roughly 65,535 available ports.
0–1023 — well-known / reserved ports (e.g. HTTP = 80, HTTPS = 443, MongoDB = 27017).
1024–49151 — registered ports, used by specific named applications.
49152–65535 — dynamic/ephemeral ports, free for short-lived use (e.g. the temporary port your browser tab uses for one connection).
Bandwidth & speed units
| Unit | Meaning | Value |
|---|---|---|
| kbps | kilobits per second | 1,000 bits/sec |
| Mbps | megabits per second | 1,000,000 bits/sec |
| Gbps | gigabits per second | 10⁹ bits/sec |
Internet connections are described by separate upload speed and download speed — most home connections are asymmetric, with download much faster than upload, since typical usage (browsing, streaming) receives far more data than it sends.
Network Delay, Throughput & Goodput
When measuring network performance, bandwidth alone is insufficient. We must track how long data takes to travel, how much arrival time varies, and how much actual data is successfully processed.
The Four Sources of Packet Delay (Nodal Delay)
A packet experiences different delays at each router hop along its path:
Guided vs unguided media
How continents are physically connected
Even satellite and radio aside, the backbone of global internet traffic is physical undersea cables — optical fiber laid across ocean floors connecting continents. You can see the actual global map of these at submarinecablemap.com, maintained by TeleGeography — it shows hundreds of named cables (2Africa, AEConnect-1, etc.) physically linking landing points across every continent.