OSI Layer: Foundations & Models
Definition
Networks are classified by geographical scale, transmission technology, ownership, and topology.
By Geographical Scale
| Type |
Range |
Speed |
Ownership |
Example |
| PAN |
1–10 m |
Low |
Personal |
Bluetooth headset |
| LAN |
Room–campus |
100 Mbps–10 Gbps |
Private |
Office/university network |
| MAN |
City (5–50 km) |
High |
Private/public |
Cable TV, metro fibre |
| WAN |
Country–global |
Variable |
Public/leased |
The Internet, PTCL backbone |
- CAN (Campus Area Network) — several LANs across one campus
- SAN (Storage Area Network) — dedicated high-speed network for storage devices
- VPN — logical private network overlaid on public infrastructure
By Transmission Technology
- Broadcast networks — single shared channel; packet carries address field, all machines receive, intended one processes (e.g., classic Ethernet, Wi-Fi)
- Point-to-point networks — many connections between individual pairs; packets may traverse intermediate nodes; routing required
By Ownership
- Private — owned and operated by a single organisation
- Public — carrier-operated, service sold to subscribers (PTCL, mobile operators)
By Connection Type
- Client-Server — centralised, easier control and security
- Peer-to-Peer — decentralised, scalable, harder to secure
Numericals
Q1 — Propagation delay by scale
Propagation speed = 2 × 10⁸ m/s.