Physical_ Basis for data communication.md (1123B)
1 +++ 2 title = "Physical: Basis for data communication" 3 +++ 4 5 # Physical: Basis for data communication 6 information can be transmitted by varying voltage on a wire 7 8 a link has properties: 9 10 - bit rate: bits per second, depends on channel’s bandwidth 11 - delay: how long it takes a bit to get to the end of the link 12 - error rate: probability of bit flipping 13 - bandwidth: analog (cutoff frequency in Hz) or digital (max data rate in bits per sec) 14 15 there are some limits to how data can be transmitted: 16 17 - bandwidth-delay product: bits have a physical size on the channel 18 - a channel can store (bit rate × delay) bits 19 - signal has a finite propagation speed, noise increases, and the signal is attenuated by km 20 - lower bandwidth limits the harmonics that can be transmitted (and decreases quality, as seen in Fourier analysis) 21 - a channel has a maximum data rate 22 - Nyquist (perfect noiseless channel): 23 - 2B log2V bits/sec 24 - B bandwidth 25 - V number of signal levels) 26 - Shannon (more realistic): 27 - B log2(1 + S/N) bits/sec 28 - B bandwidth 29 - S/N signal strength to noise ratio