передача информации по линии связи;
передача информации от одной станции к другой;
передача информации через систему узлов;
передача информации для конкретного прикладного процесса.
The physical layer defines the means of transmitting raw bits rather than logical data packets over a physical link connecting network nodes.
The major functions and services performed by the physical layer are the following:
Establishment and termination of a connection to a communications medium.
Participation in the process whereby the communication resources are effectively shared among multiple users. For example, contention resolution and flow control.
Modulation or conversion between the representation of digital data in user equipment and the corresponding signals transmitted over a communications channel. These are signals operating over the physical cabling (such as copper and optical fiber) or over a radio link.
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