This has to be done by some physical effect.

There are three main methods of transferring data:

Electrical:

A multi-wired cable with a socket at each end is used to connect the various devices together e.g. computer to hub, hub to switch or switch to router etc.

The Ethernet network cable shown above transfers data by means of electrical signals. A typical network cable called 'Cat 5' is used which is especially designed to carry the signal as efficiently as possible.

Radio or Microwave

Microwaves are just a small part of the radio spectrum, but because they are so widely used, they tend to be called by their own name.

Data is sent out through aerials mounted on tall towers. The 'cable' is effectively the microwave link between towers. Some large companies use microwave towers spread along hilltops to allow one office to communicate with others in the same country.

They do this because it is cheaper than renting telephone lines for carrying the same amount of data.

On a much smaller scale, laptops can communicate with the local area network with radio links:

Infra-Red

This is a very familiar method of transferring data if you are at all aware of your remote control ! The television remote control makes use of an infra-red link.

PDA and personal organisers often make use of an infra-red link to synchronise calendars and 'to-do' lists.