OSI Physical Layer

The physical layer of the OSI reference model is responsible for the transmission and receipt analog signals that represents digital bits.

The transmission media on the physical layer can either be cabled or wireless. Transceivers, repeaters, hubs, and media converters operate at the physical layer. The physical layer specifies:

• the physical topology
• the physical interface
• signaling

The Physical Topology

The layout of nodes and links as established by the transmission media. An area of a larger network is called a segment. A network is typically divided into segments to cope with the physical restrictions of the network media used, to improve performance, or to improve security. At the Physical layer, a segment is where all the nodes share access to the same media.

The Physical Interface

Mechanical specifications for the network medium. For cabled media, this means the construction of the cable, the interface/connector form factor, and the number and functions of the pins in a connector. For wireless media, it means radio transceiver and antenna specifications.

Signaling

The process of transmitting and receiving encoded data over the network medium. A modulation scheme describes how electrical, light, or radio signals represent bits. Timing and synchronization schemes ensure senders and receivers can identify groups of signals as a chunk or frame of data.