Wi-Fi

Lina is on vacation. She uses her mobile phone to log on to the hotel's wireless network, the hotel's WiFi. How can the phone and the network connect with each other without cables? There is a small antenna inside Lina's mobile phone that receives and transmits radio waves. And over there is a device with two antennas which also receive and send radio waves.

This is the device that Lina's phone is communicating with. The first thing this device does is add Lina’s phone’s reference number to a list. Her phone gets a unique address in this network. There are many mobile phones and computers listed here. For them all to receive the correct information from the device, they all need their own address.

Now that Lina’s phone has an address, it has the right to connect with - to access - the hotel's WiFi. The device with the two antennas is an access point. Lina has received a message from Maria who is on holiday at Mount Kilimanjaro in Kenya. Maria has sent a link to a video. Lina clicks on the link.

And here comes Maria's video. It is divided into small packages of information. The information packages have travelled by many different routes to reach Lina’s hotel. The access point checks the address for each package, and sees that.. it's the address that it gave to Linas's phone.

So the access point sends all the packages to her phone. When the access point selects the route for packages in this way, it is functioning as a router. This device, therefore, is both an access point and a router. The packages are sent from the router’s antennas to the phone antenna. Now the video is on its way to Lina’s phone.

The phone assembles all the packages that make up Maria's video. Meanwhile, Lina goes up to her hotel room. Oh, now the video has stopped. It’s just stuck. Why?

The antennas on the router transmit and receive radio waves. The number of wave peaks sent per second is the frequency. Frequency is measured in oscillations per second, hertz. The router uses two different frequencies: 2.4 billion oscillations per second - 2.4 gigahertz And 5 billion oscillations per second - 5 gigahertz. The 5 gigahertz frequency sends packages a bit faster.

So Lina has chosen to connect with that frequency. But the lower frequency - 2.4 gigahertz - can transmit through walls more easily. If there are many walls between the router and Lina’s phone, the 2.4 gigahertz frequency can work better than the 5 gigahertz. Lina is no longer on the same floor as the router’s antennas. Walls and floors diminish the signals from the antennas.

So she tries changing to 2.4 gigahertz to see if the video starts playing again. ..And it does. Now she can watch the video that Maria sent her.