This process is broken down into seven layers; Application Layer, Presentation Layer, Session Layer, Transport Layer, Network Layer, Data Link Layer, and Physical Layer. When a person communicates to another person on a network the information passes through these layers.
Ptolemy was an astronomer and mathematician. He believed that the Earth was the center of the Universe. The word for earth in Greek is geo, so we call this idea a geocentric theory.
Our understanding of the universe has changed over time. Different civilisations have created different models to explain what the universe is and how the universe began. The Greek astronomer Ptolemy (c90-168AD) used measurements of the sky to create his geocentric model. This had the earth at the centre and all the planets and the sun orbiting around it.