LAN, Backbone, MAN, WAN (Organisational Networks)
Context: FIT1047_MOC · how an ORGANISATION assembles networks at every scale — deepens the reach ladder from Computer Networks (Components and Types) with ownership, technology and the WAN buy-vs-lease decision
Quick Revision
- 🎯 Objective: LAN (floor/building, owned, switched Ethernet/WiFi) → backbone (campus, owned, fibre) → MAN/WAN (cities+, leased from carriers).
- 📦 Core Components: access/distribution/core layer architecture ➔ WAN options: dedicated circuits vs packet-switched carrier vs VPN-over-Internet.
- ⚡ Key Constraint: the WAN trade-off triangle — dedicated (guaranteed, dear) vs carrier packet-switched (shared, simpler) vs VPN (cheapest, no guarantees).
📝 Core
- LANs ➔ switched Ethernet or WiFi; end-user + server access; ≤ ~100 m; fully owned/operated; similar devices grouped.
- Backbones ➔ high-speed links BETWEEN LANs (floors, buildings); owned; fibre physical layer + switches/routers; gateway to MANs/WANs/Internet.
- Hierarchy (lecture architecture) ➔ floor Ethernet switch (access layer) → building distribution switch (distribution layer) → precinct switch/router (core layer).
- Why lease WANs ➔ cables over public land need licences; carriers (Telstra, Optus) amortise them across customers — build-your-own rarely rational.
The three WAN options
| Option | Mechanism | Properties |
|---|---|---|
| dedicated circuits | leased full-duplex point-to-point (T-carrier, SONET, Metro Ethernet), flat monthly fee | guaranteed bandwidth + latency; your routers at each end |
| packet-switched WAN | carrier’s shared packet network via a point-of-presence (POP) | shares circuits with other customers; increasingly plain Ethernet (no special kit, common expertise) |
| VPN over Internet | software “virtual NIC”; packets encapsulated + encrypted, tunnelled gateway-to-gateway | available everywhere, cheap, flexible — but NO performance guarantees, slower than dedicated |
- VPN mechanics ➔
Hello!→ VPN gateway encrypts/encapsulates ($U1&x#3) → travels the public Internet inside the tunnel → far gateway unpacks → delivers into the remote LAN as if local.
⚠️ Common Mistakes
- 💡 MAN ≈ WAN ➔ the lecture treats them as the same idea at different distances — don’t invent extra differences.
- 💡 “Private” in VPN is cryptographic, not physical ➔ the bits ride the public Internet; privacy comes from encryption + encapsulation only.
- 💡 Why not just the Internet? ➔ the stock answer triple: security, reliability, performance — VPN patches the first, never the last two.
🧠 Active Recall
A company connects Melbourne and Penang offices. Walk the three options and what each buys.
Answer
- Short answer: Dedicated leased circuit (guaranteed bandwidth/latency, highest cost) · carrier packet-switched service via POPs (shared, moderate) · VPN over each office’s Internet link (cheapest, zero guarantees).
- Why: Pay for certainty ➔ the options price exactly one thing — how much performance is contractually yours.
Sketch the access/distribution/core hierarchy and place switch vs router at each level.
Answer
- Short answer: Floor switches (access) → building distribution switches → precinct core switches/routers toward WAN/Internet.
- Why: Aggregate then route ➔ cheap layer-2 fan-out at the edge; layer-3 intelligence concentrated where networks meet (switch vs router).