Physical Layer

Every output, transfer and reception of information takes place by way of a physical medium, meaning a carrier of this information. Also on the Internet, the transfer of information is conducted via a medium of physical communication. These range from traditional electric conductors, simple cables and fiber-optic cables (fiberglass cables) to conductor-independent forms, whereby electromagnetic waves in different frequencies serve as information carriers. But how does the information to be transferred, digitally coded as a series of "zeros" and "ones," actually arrive at the physical communications medium? Before taking a detailed look in this chapter at the different wired and wireless media of transfer, the theoretical foundation of physical data transfer will be explained, whereby so-called modulation procedures and multiplex procedures stand at the forefront of how this binary information is put into a physically transferable "form," thus enabling an efficient data transfer, also over shared media.