Networking: Devices, Topologies & Protocols

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Network types and topologies

⏱ 4 min read🧩 6 question types🎯 20 practice Q

The idea in one minute

Networks are named by how far they reach: PAN, LAN, MAN and WAN, from small to large. A topology is the shape of the wiring: bus, ring, star, mesh, tree or hybrid. Star is the shape used in modern offices. A full mesh of n computers needs n(n-1)/2 links.

Networks by their reach

Name a network by how far it stretches. The order is PAN, then LAN, then MAN, then WAN.

Type	Span	Everyday example
PAN (Personal Area Network)	about 10 metres around one person	Bluetooth headset with a phone
LAN (Local Area Network)	one building or campus	school computer lab, office floor
MAN (Metropolitan Area Network)	one city	city cable network
WAN (Wide Area Network)	countries or continents	the Internet is the largest WAN

A LAN is privately owned and fast. A WAN uses leased lines over long distances.

Tip: Match the span in the question, not the technology. "One office building" is always a LAN.

Topologies, the shape of the wiring

A topology is the way computers are laid out and joined. Learn the table row by row.

Topology	Layout	Strength	Weakness
Bus	all nodes tap one backbone cable with terminators	cheapest	backbone break kills all; collisions
Ring	each node joins exactly two neighbours	orderly token passing	one break can halt the loop
Star	every node joins a central hub or switch	one cable failure hurts one node only	the central device is a single point of failure
Mesh	every node joins every other node	most reliable	most cables, costliest
Tree	hierarchy of stars joined on a bus	scales to large LANs	root failure splits the tree
Hybrid	a mix of the above	fits real networks	more complex

Rule: Star is the most common shape today. Mesh is the most reliable.

Counting mesh links

In a full mesh of n computers, each one has n - 1 links. Every link is counted twice that way, so halve the total.

\text{links}=\dfrac{n(n-1)}{2}

Example: For 6 computers, $6\times5\div2=15$ links. For 8 computers, $8\times7\div2=28$ links.

Never use $n^2$ . Check small cases: 4 computers give 6 links, 5 give 10.

Client-server, peer-to-peer and VPN

Client-server: dedicated servers serve many client machines.
Peer-to-peer: all machines are equals. Each can share and use resources.
VPN: builds an encrypted private tunnel over a public network.

Wireless and IEEE standards

Ethernet (wired LAN) is IEEE 802.3.
Wi-Fi (wireless LAN) is IEEE 802.11. The versions n, ac and ax are called Wi-Fi 4, 5 and 6.
Bluetooth is IEEE 802.15. It is a PAN of about 10 metres.
Infrared needs a clear line of sight.

Watch: Wi-Fi is not 802.3. The number 802.3 belongs to wired Ethernet.

Question types you will see

Each type: how to recognise it, the method step by step, and one question to try.

Type 1very common4 practice Q

Network type by span

How to spot it:

A situation is described (school lab, city cable, worldwide web, one person's Bluetooth) and PAN, LAN, MAN or WAN is asked.

Method

Line up the ladder: PAN, LAN, MAN, WAN.
Find the span in the question: person, building, city or world.
Pick the type with that span.
Remember the Internet is the largest WAN.

Why it works:

The span, not the technology, names the network.

Try this

A computer lab of one school connected by a switch forms a

Show solution

The lab is inside one building.
One building means a local span.

Answer

LAN (Local Area Network)

Type 2very common4 practice Q

Topology identification by description

How to spot it:

The layout is described (all nodes to a central device, every node to every other, one backbone, a circle) and the topology is asked.

Method

Central device with all nodes on it: Star.
Every node linked to every other: Mesh.
One shared backbone cable with terminators: Bus.
Closed circle of neighbours: Ring. Stars joined on a backbone: Tree.

Why it works:

Each topology has one giveaway layout phrase.

Try this

In which topology is every computer connected to a central hub or switch?

Show solution

Central hub or switch is the giveaway.
One cable break isolates only one node.

Answer

Star topology

Type 3common3 practice Q

Mesh link count (numeric)

How to spot it:

How many links are needed for a full mesh of n computers? It is pure arithmetic.

\dfrac{n(n-1)}{2}

Method

Write the formula n(n-1)/2.
Put in n and multiply n by n - 1.
Halve the product.
Check with n = 4 giving 6.

Why it works:

Each line is counted twice if you multiply n by n - 1.

Try this

How many cable links are needed for a full mesh of 6 computers?

Show solution

6 x 5 = 30.
30 / 2 = 15.

Answer

15 links

Type 4common3 practice Q

Topology strengths and failure points

How to spot it:

A statement says which topology is cheapest, most reliable, has a single point of failure, or what happens when a cable breaks.

Method

Star: one cable break hurts one node. Hub failure stops all.
Bus: backbone break means total failure. It is the cheapest.
Mesh: most reliable, most cable, costliest.
Ring: one broken node or link can stop the ring.

Why it works:

The weakness of each shape follows from how it is wired.

Try this

In a star topology, failure of the central hub results in

Show solution

Every node depends on the hub.
Individual cables do not matter here.

Answer

The whole network stops communicating

Type 5occasional2 practice Q

IEEE standards and LAN jargon

How to spot it:

Wi-Fi is IEEE what, or Ethernet works on which standard. It is matching 802.x numbers to technologies.

Method

Ethernet (wired) is 802.3.
Wi-Fi (wireless) is 802.11.
Bluetooth is 802.15.
Watch for the trap of pairing Wi-Fi with 802.3.

Why it works:

The 802 family names the wire or the air.

Try this

Wi-Fi networks are standardised under IEEE

Show solution

Wi-Fi is wireless LAN.
802.3 is wired, 802.15 is Bluetooth.

Answer

802.11

Type 6occasional

Network models, VPN and wireless links

How to spot it:

Questions ask what a VPN does, how client-server differs from peer-to-peer, or the range of Bluetooth.

Method

VPN: an encrypted private tunnel over a public network.
Client-server: dedicated servers serve clients.
Peer-to-peer: all machines are equals.
Bluetooth is a PAN of about 10 m. Infrared needs line of sight.

Why it works:

Each term has one short definition to recall.

Try this

Which technology builds an encrypted private tunnel over a public network?

Show solution

The key words are encrypted and private tunnel.
Public network means the Internet.

Answer

VPN (Virtual Private Network)

Shortcuts that save time

⚡ Mesh half-row sum

Full-mesh links for n nodes are n(n-1)/2. Compute it each time. Do not memorise per-n values.

Example

How many links does a full mesh of 8 computers need?

Show solution

Each computer has 7 links.
8 x 7 = 56, and each link is counted twice.
56 / 2 = 28.

Answer

28 links

⚡ PLMW span ladder

PAN < LAN < MAN < WAN: Personal, Local, Metropolitan, Wide. The Internet is the largest WAN.

Example

A network limited to one office building is a?

Show solution

One building is a local span.
Local Area Network.

Answer

LAN

⚡ Star means central device

If the question says the central device fails and the whole network stops, it describes star topology.

Example

In which topology is the central hub a single point of failure?

Show solution

Every node hangs off the hub.
If the hub fails, none can talk.

Answer

Star topology

Mistakes to avoid

Where most students lose marks on this subtopic.

Mistake 01

Using the bus topology's weakness (backbone break) for star questions.

Star fails at the central hub or switch. Bus fails at the backbone.

Mistake 02

Counting mesh links as $n^2$ .

Use n(n-1)/2. Each link is counted once, not twice.

Mistake 03

Calling Wi-Fi IEEE 802.3.

802.3 is wired Ethernet. Wi-Fi is 802.11.

Mistake 04

Calling the Internet a MAN or a LAN.

The Internet is the largest WAN.

Quick revision

Read this the night before the exam.

PAN (10 m) < LAN (building) < MAN (city) < WAN (country or world).
The Internet is the largest WAN.
Bus = one backbone. Ring = circle of neighbours. Star = central hub or switch. Mesh = all to all.
Full-mesh links = n(n-1)/2. Six computers give 15 links.
Star's weakness is the central device. Bus's weakness is the backbone.
Ethernet is 802.3, Wi-Fi is 802.11, Bluetooth is 802.15.

Practice: 20 questions

Sets of 10, mixed across the question types above. Every answer has a step-by-step explanation.

Topic test · 10 questions

Suggested time 5 min · wrong answers go to your mistake notebook automatically.

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