CAP7001 · Unit 1: Network basics
Network design, topologies and classifications
10 practice questions · in the MTE and ETE syllabus
Key points
- Mesh links = n(n-1)/2; ports per device = n-1
- Star: hub failure kills the network
- Bus: single backbone with terminators
- LAN < MAN < WAN by coverage
A network topology is the physical or logical arrangement of links and nodes. The four basic topologies are mesh, star, bus and ring.
| Topology | Key feature | Weakness |
|---|---|---|
| Mesh | Dedicated link between every pair | Many cables and ports |
| Star | Each node connects to a central hub or switch | Hub is a single point of failure |
| Bus | One backbone with drop lines and terminators | Backbone fault affects the whole bus |
| Ring | Each node connects to two neighbours | A break can disable a simple ring |
For a fully connected mesh of n devices: duplex links = n(n-1)/2, ports per device = n-1.
Worked example: 8 devices need 8 x 7 / 2 = 28 links and 7 ports each. Growing to 9 devices adds 8 links and one port on every existing device.
Networks are also classified by size: LAN (building or campus), MAN (city), WAN (country or world).
Exam pitfall: forgetting to divide by 2 gives n(n-1) links (56 for n = 8). Each duplex link serves two devices.
Try two questions
A network that covers a city and is larger than a LAN but smaller than a WAN is a:
- MAN
- SAN
- VPN
- PAN
Show the answer
A. LAN < MAN < WAN by geographic coverage.
Six computers are joined either in a full mesh or in a star around one switch. A cable costs 100 per link, a network port costs 20 each, and the switch costs 500 including its own ports. The mesh needs a port on each device for every other device. How much cheaper is the star?
- 880
- 780
- 1500
- 980
Show the answer
A. The mesh has 15 cables (1500) and 30 device ports (600), a total of 2100. The star has 6 cables (600), 6 device ports (120) and the switch (500), a total of 1220, so the saving is 880.
Why not B: That counts the switch ports on top of the 500 cost, and so charges them twice.
Why not C: That is the cable cost of the mesh alone, not the difference between the totals.
Why not D: That forgets the 6 device ports in the star's cost.