Network hardware and connections

NICs, switches, routers and access points; copper, fibre and wireless; Wi-Fi, Ethernet and Bluetooth.

F10.2NetworksGCSE15 min

Do this lesson in the simulator

A network needs hardware to connect each device, and a way for the bits to travel between them: cables or radio waves. This lesson names the boxes you would find in a school's network cupboard, compares wired with wireless, and builds a model of the switch, the device at the centre of most LANs.

The hardware

Hardware What it does
Network interface card (NIC) connects a device to a network. Every NIC has a unique MAC address set when it is made. Today it is usually a chip built into the device
Switch connects the devices in a LAN. It reads the MAC address on each frame of data and sends it only to the device it is for
Router connects different networks together, such as a school's LAN to the internet. It reads the IP address on each packet and sends it on towards its destination
Wireless access point (WAP) lets devices connect to a wired network by radio: Wi-Fi
Transmission media what the data travels through: copper cable, fibre optic cable, or radio waves

A home "router" is several of these in one box: a router, a switch, a wireless access point and a modem.

Transmission media

  • Copper cable (Ethernet cable) carries data as electrical signals. It is cheap, but the signal weakens over about 100 m.
  • Fibre optic cable carries data as pulses of light. It is faster and works over many kilometres without interference, but costs more.
  • Radio waves carry wireless data. No cables are needed, but walls, distance and other devices weaken the signal.

Wired and wireless

Wired (Ethernet) Wireless (Wi-Fi)
Speed usually faster usually slower, and shared
Reliability steady; little interference affected by walls, distance and other networks
Security someone needs a physical connection signals can be picked up outside the building, so they must be encrypted
Movement devices stay where the cable is devices can move around
Cost to set up cables must be run to every device fewer cables

Wi-Fi is the standard for wireless LANs, using radio at 2.4 GHz or 5 GHz, split into channels so that nearby networks do not interfere. It is encrypted with a standard such as WPA2 or WPA3, so a device needs the password to join and cannot read other people's data. Bluetooth is a short-range wireless standard for connecting a few devices close together, such as a phone and earbuds: a PAN. Ethernet is the standard for wired LANs.

BugBot's Vision board has a separate chip just for Wi-Fi, which links the robot to its USB dongle, while a USB cable connects it directly to a computer.

How a switch learns

A switch starts knowing nothing. Each time a frame arrives, it notes which port that sender's MAC address is on. When a frame is for an address it already knows, it sends it to that port only. When it does not know, it sends it out of every port:

# the two lines every program starts with: the commands, then the robot
from bugbot import *
connect()

table = {}                                  # MAC address -> port
frames = [(1, "AA-01", "BB-02"), (2, "BB-02", "AA-01")]   # (port it came in on, from, to)
for port, source, destination in frames:
    table[source] = port                    # learn where the sender is
    if destination in table:
        print(source, "->", destination, ": port", table[destination])
    else:
        print(source, "->", destination, ": every port")
print(table)

Run this in the simulator

Task: a learning switch

Complete the switch. For each frame in frames, learn which port its source is on. Then print frame to <destination>: port <n> if the destination is known, or frame to <destination>: every port if not. At the end, print learned <n> addresses.

# the two lines every program starts with: the commands, then the robot
from bugbot import *
connect()

# (port it came in on, source MAC, destination MAC)
frames = [
    (1, "AA-01", "BB-02"),
    (2, "BB-02", "AA-01"),
    (3, "CC-03", "AA-01"),
    (1, "AA-01", "CC-03"),
    (4, "DD-04", "BB-02"),
]
table = {}

Challenges

  1. A hub is an older device that sends every frame out of every port. Count how many frames a hub would have sent to the wrong device.
  2. Add a frame from a device that has moved to a different port. What should the switch do?
  3. A school is building a new sports hall 400 m away. Recommend copper, fibre or wireless for the link, with two reasons.