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.
Ptolemy's conception of the universe, with the earth as the fixed center and the heavenly bodies moving about it. (tÅlâ²É-mÄâ²Ä­k). Ptolemaic system. Ptolemy believed that Earth was at the center of the universe and that the sun and planets orbited Earth (with the planets also moving in smaller circles called epicycles).