Fiber Optic Glossary: Numbers

1U: Abbreviation for “one unit.” “U” = 1.75 inches.
4B5B Encoding: A signal modulation scheme in which groups of four bits are encoded and transmitted in five bits in order to guarantee that no more than three consecutive zeroes ever occur; used in FDDI.
4:1:1: The set of sampling frequencies used to digitize the luminance and color difference components (Y, R-Y, B-Y) of a video signal. The four represents 13.5 MHz, the sampling frequency of Y, and the ones each 3.75 MHz for R-Y and B-Y.
4:2:0: A sampling system used to digitize the luminance and color difference components (Y, R-Y, B-Y) of a video signal. The four represents the 13.5 MHz sampling frequency of Y, while the R-Y and B-Y are sampled at 6.75 MHz — effectively between every other line only (one line is sampled at 4:0:0, luminance only, and the next at 4:2:2).
4:2:2: A commonly used term for a component digital video format. It is generally used as shorthand for ITU-R 601. 4:2:2 is the standard for digital studio equipment.
4f_sc: Abbreviation for four times the frequency of SC (subcarrier). The sampling rate of a D2 digital video signal with respect to the subcarrier frequency of a video signal. The 4f_sc frequency is 14.3 MHz in NTSC and 17.7 MHz in PAL.
8B10B Encoding: A signal modulation scheme in which eight bits are encoded in a 10-bit word to ensure that too many consecutive zeroes do not occur; used in ESCON and fibre channel.
802.3 Network: A 10 Mb/s CSMA/CD bus-based network; commonly called Ethernet.
802.5 Network: A token-passing ring network operating at 4 Mb/s or 16 Mb/s.
10BASE-F: A fiber optic version of an IEEE 802.3 network.
10BASE-FB: That portion of 10BASE-F that defines the requirements for a fiber backbone.
10BASE-FL: That portion of 10BASE-F that defines a fiber optic link between a concentrator and a station.
10BASE-FP: That portion of 10BASE-F that defines a passive star coupler.
10BASE-T: A twisted-pair cable version of an IEEE 802.3 network.
10BASE-2: A thin-coaxial-cable version of an IEEE 802.3 network
10BASE-5: A thick-coaxial-cable version of an IEEE 802.3 network; very similar to the original Ethernet specification.