defines the physical characteristics of the transmission medium (connectors, pins, electrical currents, encoding, light modulation, etc) rj-45, ethernet (ieee 802.3) lan hub, lan repeater, cables
defines the physical characteristics of the transmission medium (connectors, pins, electrical currents, encoding, light modulation, etc) rj-45, ethernet (ieee 802.3) lan hub, lan repeater, cables
defines the hardware, cabling wiring, power output, pulse rate, etc. (osi layer)