Mobile networks

Maria is on a safari out on the savannah in Kenya. There are giraffes, lions, strange trees, zebra .. .. was that really a tree? No, it's a big construction that sends signals - radio waves. It's a telephone mast.

The telephone mast is needed for Maria to call or use the Internet when she is on the savannah. To get in touch with the telephone mast, Maria's phone has an antenna. When the phone is switched on and not in airplane mode, the antenna receives and transmits radio waves. The telephone mast also has antennas that receive and transmit radio waves. When the mobile phone comes close enough to the mast, the antennas get in touch.

But where do the signals transmitted by the mast come from? Well, they come from this little building that’s close to the mast. A cable goes down from the antennas in the mast to a device, some hardware, inside this building. The antennas and the hardware together are called a base station. The base station sends and receives signals through its antennas.

When the base station receives signals from Maria's phone, it passes the signals to another device, which makes sure that the call reaches the right person, who could be anywhere in the world. This other device is a mobile switch. The mobile switch also handles information packets from the Internet, sending them in both directions to the right computers or phones. How does the mobile switch know that it's Maria’s phone that’s connecting to the base station? There’s a small card, a SIM card, her Subscriber Identity Module, inside her phone..

which contains her international mobile identification and her phone number. The SIM card also saves information about which base station the phone had contact with most recently. Now Maria is calling her grandmother. The signal goes from the phone, to the mast, down to the base station and onwards to the mobile switch. The SIM card tells the mobile switch that Maria is currently paying for an account and she can call and surf with her phone. - Hi gran!

It is Maria.. - As Maria talks, she goes further and further away from the mast. What happens then? Well, the mobile switch stops listening to this base station because it’s now getting a weaker signal, and starts listening to another base station that’s picking up a stronger signal. When the mobile switch switches base station, it saves the new base station’s number. The SIM card in the phone also saves that number.

This enables Maria to keep talking to her grandmother, even though the minibus travels from one telephone mast to the other. But there must be more exciting things to do while on safari than talk to your grandmother.. Let’s bring in some elephants. - Oh, super cute elephants! Got to go! Hugs and kisses!