Networks¶

Network types Network components Practical 1.4 PDF

You send a WhatsApp to the friend sitting right next to you. It arrives in less than a second. But here is the surprise: that message probably did not jump the one metre between your phones. It went out through Wi-Fi or 4G, crossed cables, routers and maybe an undersea fibre, reached a WhatsApp server in a data centre, and came all the way back. How does it find the way?

That is what a network is for. Every game you play online, every video you stream, every photo you back up to the cloud depends on it. And this very classroom is a network you can draw on the whiteboard.

What is a network?¶

A network is two or more devices connected so they can exchange information.

Remember the three verbs from What is a computer?: store, transform, transfer. A network is all about the third one — moving bits from one computer to another.

Any network, from two phones sharing a photo to the whole Internet, needs the same three things:

The rules have a name: protocols. Two people who don't share a language cannot talk even if they are in the same room; two computers without a common protocol can't either. You will study protocols in detail — the famous OSI and TCP/IP models — in Unit 3. For now, just remember they exist.

Types of networks by scope¶

The first way to classify a network: how far does it reach?

A LAN that uses radio instead of cables is called a WLAN (Wireless LAN). Your home Wi-Fi is a WLAN.

flowchart LR
    PAN["<b>PAN</b><br>a few metres<br>earbuds, watch"] --> LAN["<b>LAN / WLAN</b><br>one building<br>home, classroom"]
    LAN --> MAN["<b>MAN</b><br>one city<br>city council network"]
    MAN --> WAN["<b>WAN</b><br>the planet<br>the Internet"]

Types of networks by topology¶

The second way to classify a network: what shape does it have? The topology is the way devices are connected to each other.

flowchart TB
    subgraph BUS ["Bus: one shared cable"]
        direction LR
        B1["PC 1"] --- BC["shared cable"] --- B2["PC 2"]
        BC --- B3["PC 3"]
    end
    subgraph STAR ["Star: everyone to a centre"]
        direction LR
        S1["PC 1"] --- SW["<b>Switch</b>"]
        S2["PC 2"] --- SW
        S3["PC 3"] --- SW
    end
    subgraph RING ["Ring: a closed circle"]
        direction LR
        R1["PC 1"] --- R2["PC 2"] --- R3["PC 3"] --- R1
    end
    subgraph MESH ["Mesh: many paths"]
        direction LR
        M1["Node 1"] --- M2["Node 2"] --- M3["Node 3"]
        M1 --- M3
    end

This classroom is a star: every computer has its own cable going to a central switch.

Components of a network¶

Now open the box. These are the pieces you will find in almost every network.

The network card and the MAC address¶

A NIC (Network Interface Card) is the part of a device that connects it to a network — the door of the house.

Every laptop, phone and console has at least one: an Ethernet port, a Wi-Fi chip, or both. Each NIC comes from the factory with a unique MAC address (Media Access Control), a 48-bit number written in hexadecimal:

A4:83:E7:2C:10:9F

• 48 bits = 6 bytes = 12 hex digits. Yes, the hex from the Binary page pays off here.
• The first 24 bits identify the manufacturer (Apple, Intel, MikroTik...); the last 24 bits are chosen by the manufacturer to tell its own devices apart.

In the postal analogy, the MAC address is the name on the door: it identifies who lives in the house. It does not say where the house is in the world — that is the job of the IP address, which you will meet in Unit 3.

Switch¶

A switch connects devices inside the same LAN and delivers each message only to the device it is for.

It is the concierge of a building: it knows which flat each name lives in, so it hands every letter to the right door instead of shouting it through the whole building. It learns this by looking at MAC addresses. The switch is the centre of a star topology.

Router¶

A router connects different networks together and chooses the path a message should take between them.

It is the post office: when a letter is for another town, the concierge gives it to the post office, which decides which road to send it down. Your home LAN and the Internet are different networks; the router sits between them. The school uses MikroTik routers like this one:

Remember from What is a computer?: a router has a CPU, memory and I/O. It is a computer whose only job is to forward information.

Access point¶

An access point (AP) lets wireless devices join a wired LAN, using radio instead of a cable.

It is a mailbox you can reach without a street: devices near it drop their letters through the air, and it passes them onto the cable network.

Modem and ONT¶

Your Internet provider's line does not "speak" the same language as your LAN. A translator sits at the edge:

• A modem (modulator–demodulator) converts your bits into the signal the provider's line uses — for example over an old copper phone line.
• An ONT (Optical Network Terminal) does the same for fibre: it turns pulses of light into electrical signals and back. If you have fibre at home, the small box where the fibre enters is the ONT.

Summary¶

The medium: cables and connectors¶

Twisted pair¶

Twisted pair cable is the typical network cable: 8 copper wires twisted in 4 pairs, ending in an RJ45 connector.

The wires are twisted because each twist cancels part of the electrical noise from neighbouring wires and from the environment. Cables are graded by category (Cat): a higher category means better protection against noise and more speed.

Notice the 100 m limit: past that, the signal gets too weak and noisy for copper. For longer runs you need something else.

Fibre optic¶

Fibre optic cable carries bits as pulses of light inside a glass thread thinner than a hair.

• Much longer distances than copper — kilometres, even across oceans in undersea cables.
• Immune to electrical noise, because light is not affected by it.
• More fragile and more expensive to install. It connects buildings, cities and continents; in homes it usually stops at the ONT.

Wireless: the medium is the air¶

Radio waves need no cable at all — the air is the medium. Convenient, but the signal weakens with distance and walls, and anyone nearby can pick it up (which is why Wi-Fi needs a password).

Communication systems: wired and wireless¶

The technologies you use every day, in one table:

A little history for each name:

• Ethernet was invented by Bob Metcalfe at Xerox PARC. His memo describing it is dated 22 May 1973. It is still the standard for wired LANs today.
• Wi-Fi is the brand name for the IEEE 802.11 standard, first published in 1997. The name "Wi-Fi" came in 1999.
• Bluetooth is named after Harald "Bluetooth" Gormsson, a 10^th-century Viking king who united Denmark and Norway — just like the technology unites devices. Its logo mixes his initials in runes: ᚼ and ᛒ.

Network maps: physical and logical¶

When a network breaks, a technician's first question is: "Where is the map?" There are two kinds:

• A physical map shows where things really are: which room, which wall socket, which cable goes to which port.
• A logical map shows how information flows: which devices talk to which, grouped by network, ignoring where they physically sit.

Here is the same small classroom drawn both ways.

flowchart TB
    subgraph RACK ["Rack in the corridor"]
        ROUTER["<b>MikroTik router</b>"]
        SWITCH["<b>Switch</b><br>24 ports"]
        ROUTER ---|"Cat6, 2 m"| SWITCH
    end
    subgraph ROOM ["Classroom 0.12"]
        direction LR
        WALL["<b>Wall sockets</b><br>patch panel A1–A20"]
        PC1["PC row 1"]
        PC2["PC row 2"]
        AP["<b>Access point</b><br>on the ceiling"]
    end
    SWITCH ---|"Cat6 runs,<br>~25 m inside the wall"| WALL
    WALL ---|"patch cable"| PC1
    WALL ---|"patch cable"| PC2
    WALL ---|"patch cable"| AP
    ROUTER ---|"fibre to the ISP"| ISP(["Internet"])

flowchart LR
    subgraph LAN ["Classroom LAN"]
        direction TB
        PCS["<b>Student PCs</b>"]
        LAPTOPS["<b>Wi-Fi laptops<br>and phones</b>"]
        TEACHER["<b>Teacher PC</b>"]
    end
    LAN <-->|"all traffic out<br>of the LAN"| ROUTER["<b>Router</b><br>the post office"]
    ROUTER <-->|"WAN"| NET(["<b>Internet</b>"])

Notice what each one hides:

• The physical map shows cable lengths and the patch panel, but says nothing about which devices can talk to each other.
• The logical map ignores cables completely: the access point and the switch disappear, because from the point of view of the information all these devices are simply "in the same LAN".

Real logical maps also show addresses and sub-networks — more on that in Unit 3.

Key takeaways¶

• A network is two or more devices exchanging information: it needs devices, a medium and common rules called protocols.
• By scope: PAN (a person), LAN/WLAN (a building), MAN (a city), WAN (the planet — the Internet is the biggest one).
• By topology: bus, star, ring, mesh. Almost every LAN today is a star around a switch.
• The NIC connects a device and carries a unique MAC address; the switch delivers inside a LAN; the router joins networks; the access point adds wireless; the modem/ONT translates the provider's line.
• Twisted pair (Cat5e/Cat6/Cat6a, RJ45, max 100 m) for short runs, fibre for long ones, radio for wireless (Wi-Fi, Bluetooth, 4G/5G).
• A physical map shows where things are; a logical map shows how information flows.

Quick check¶

Next: stay safe while you open and handle all this hardware — Health and safety.