note02-Computer Network

2. Physical Layer

Communication system Model (source, transmitter->xxx-> receiver, end), the source emits a digital signal, the modulator is encoded as an analog signal for transmission, the demodulator decodes the analog signal to the end of the digital signal

Signal-to-noise ratio, Shannon formula,C=B log2 (1+S/N). Type:B is the channel bandwidth (Hz),S is the signal power (watts),N is the noise power (watts)

Simplex (Unidirectional communication class such as broadcast), half-duplex (one side of the receiver), full duplex (a party can send and receive)

Encoding (bitstream, zero, Zero, Manchester, differential Manchester)

Modulation (amplitude adjustment, frequency adjustment, modulation phase)

Channel Multiplexing Technology (frequency division multiplexing, time division Multiplexing, statistical time division multiplexing, Wavelength Division multiplexing)

Access Mode (ASDL asymmetric digital subscriber line, isp=atu-c------splitter----ATU-R Modem---userpc)

HFC Hybrid fiber access

note02-Computer Network