A network is two or more devices that can exchange data. Networks are grouped by how much ground they cover:
| Type | Covers | Example |
|---|---|---|
| PAN | A few metres | Phone to Bluetooth earbuds |
| LAN | A room, floor or campus | Your college lab, home Wi-Fi |
| MAN | A city | A cable operator's city network |
| WAN | Countries, continents | The internet, a bank's branch network |
A LAN is owned by one organisation, is fast (1–10 Gbps is common) and has low delay. A WAN usually runs over links leased from telecom providers, is slower per rupee and has much higher delay.
Two kinds of delay show up in numericals:
- Transmission delay = data size ÷ bandwidth. Time to push all the bits onto the wire.
- Propagation delay = distance ÷ signal speed. Time for one bit to travel the length of the link.
1,000,000 bytes over 8 Mbps: 8,000,000 bits / 8,000,000 bps = 1 s
4000 km at 2 x 10^8 m/s: 4,000,000 m / 2 x 10^8 m/s = 20 msThe trap: mixing bits and bytes. Bandwidth is in bits per second, file sizes are usually in bytes. Multiply bytes by 8 first.
In interviews: "Is the internet a LAN or a WAN?" It is the largest WAN, a network of networks.