Z

z-axis - The third axis, usually representing depth, of a three-dimensional grid, chart, or graph in a Cartesian coordinate system.The z-axis is perpendicular to both the x-axis and y-axis and is used to plot the value of z, the third unknown in mathematics. See also Cartesian coordinates, x-axis, y-axis, and z.

Z - 1. Zeta.The sixth letter of the Greek alphabet, written in the English alphabet as Z. 2.The symbol for impedance. See impedance. 3. The symbol for Zulu time. See Zulu time. 4. Zetta sextillion (10 21 ), or 1,000,000,000,000,000,000,000. See ZB. 5. In mathematics, the third of a set of unknown variables, with x and y being the first two unknowns. See also x, y, and z-axis. 6. One of the two letters, along with Q, that traditionally did not appear on a telephone dial or keypad.The thought was that Z could be confused with 2 and that Q could be confused with O. Z now appears with W, X, and Y on number 9. Alphanumeric dialing was, and remains, a North American practice. Telephones in most other countries do not sport letters.

ZB (ZettaByte) - A sextillion (10 ²¹ ) bytes. In computing and storage systems, a ZB is exactly 1,180,591,620,717,411,303,424 (2 ⁷⁰ ) bytes, since the measurement is based on a base 2, or binary, number system.The term ZB comes from the fact that 1,180,591,620,717,411,303,424 is nominally, or approximately, 1,000,000,000,000,000,000,000, which suggests that mathematicians consider a difference of 180,591,620,717,411,303,424 to be a rounding error. See also byte and Z.

ZC (ZigBee Coordinator) - A ZigBee device that initializes the network, coordinates its operation, and is responsible for security. There is one ZC per network, but there can be a great many ZigBee End Devices (ZEDs) and ZigBee Routers (ZRs). See also ZED, ZigBee, and ZR.

ZDSF (Zero Dispersion-Shifted Fiber) - A type of dispersion-shifted, single-mode fiber (DSF SMF) that shifts the point of zero dispersion by increasing material dispersion to the point that it cancels out chromatic dispersion at 1550 nm, rather than 1310 nm. Dense Wavelength Division Multiplexing (DWDM) and Erbium-Doped Fiber Amplifiers (EDFAs) both work in this higher window, which can create yet another noise problem in the form of four-wave mixing (FWM), a phenomenon by which wavelengths interact to create additional wavelengths.The EDFAs amplify those signals, and superimpose them on the DWDM channels. Non Zero Dispersion-Shifted Fiber (NZDF) addresses this issue by shifting the optimal dispersion point slightly above the range in which EDFAs operate. See also chromatic dispersion, cladding, core, dispersion, DSF, DWDM, EDFA, material dispersion, noise, NZDF, refractive index, SMF, wavelength, and window.

ZED (ZigBee End Device) - A ZigBee terminal device, such as a sensor, that can perform only a single monitoring or control function. A ZED comprises a low-cost microprocessor, RAM and ROM, a long-life battery, and a low-power radio and controller.A ZED is small enough to be embedded in a light switch, smoke or carbon dioxide detector, thermostat, security sensor, utility meter, or medical sensor. A ZED can communication only with a ZigBee Router (ZR), and not other ZEDs. See also ZigBee and ZR.

Zener Diode - A diode that operates in the reversed biased/avalanche mode. When a zener diode is in this mode, it has a constant voltage from its anode to cathode. Zener diodes are used to regulate voltage, and they are available in many voltage values, such as 5 V, 12 V, 24 V, etc.

zero dispersion-shifted fiber (ZDSF) - See ZDSF.

Zero Suppression - To omit zeros from a number field.

Zero-Byte Time-Slot Interchange - A method of line coding, where the quantity of zeros transmitted is reduced. The reduction is accomplished by recognizing bytes that are all zeros (eight consecutive bits) and replacing them with an alternate byte (or flag) that does not contain all zeros.

zero-water-peak fiber (ZWPF) - See ZWPF.

ZigBee Alliance - An association of companies working to develop and promote a set of open, global standards for a low-power, cost effective wireless personal area network (WPAN) technology based on IEEE 802.15.4. For contact information, see Appendix A. See also WPAN and ZigBee.

ZigBee Coordinator (ZC) - See ZC.

ZigBee End Device (ZED) - See ZED.

ZigBee principle - The technique that a domestic honeybee uses to communicate the location of a new food source to other members of the colony.The bee dances in a zigzag pattern that communicates information such as distance and direction, at least according to the ZigBee Alliance, which developed and promotes the ZigBee specification for a wireless personal area network (WPAN). My personal research, as well as the research of many others, suggests there is no such thing, at least not until the ZigBee Alliance coined the term. Oh, well. See also WPAN, ZigBee, and ZigBee Alliance.

ZigBee Router (ZR) - A ZigBee device that functions as a router to pass messages from ZigBee End Devices (ZEDs) to other ZRs or to the ZigBee Coordinator (ZC).A ZR also can function as a ZED. See also ZC, ZED, and ZigBee.

ZigBee Router (ZR) - See ZR.

ZigBee - A specification from the ZigBee Alliance for a set of high-level communications protocols based on the IEEE 802.15.4 standard for a low-data-rate wireless personal area network (WPAN) comprising devices of low complexity and long battery life. ZigBee is designed for connecting devices in ad hoc networks over very short distances with very low power consumption. ZigBee specifies star, peer-to-peer and mesh network topologies, with mesh being the preferred approach for reasons of redundancy and resiliency. ZigBee runs in the ISM band using direct sequence spread spectrum (DSSS) transmission. A ZigBee Coordinator (ZC) initializes the network, coordinates its operation, and is responsible for security. ZigBee End Devices (ZEDs) are terminal devices that are very limited in function, and can communicate only with ZigBee Routers (ZRs), which function to pass messages to other ZRs or to the ZC. In beacon enabled networks, ZigBee Routers (ZRs) periodically beacon their presence and, therefore, need power up only during the beaconing cycle, which conserves battery life. In non–beacon enabled networks, all devices remain active all the time and employ the carrier sense multiple access with collision avoidance (CSMA/CA) medium access control (MAC) mechanism. Although most devices run in the 2.4 GHz range, some run at 915 MHz (Americas) and 868 MHz (Europe) ranges, as those bands offer better signal propagation through physical obstructions such as walls, floors, ceilings, and windows. Depending on the frequency band selected, raw data rates are 20 kbps (1 channel at 868 MHz), 40 kbps (10 channels at 915 MHz), and 250 kbps (16 channels at 2.4 GHz). Specified modulation techniques are binary phase-shift keying (BPSK) in the 868 and 915 MHz bands, and quaternary phase-shift keying (QPSK) in the 2.4 GHz band. Distances range from 10 meters to 100+ meters, depending on frequency, power output, and environmental characteristics. Devices generally transmit at a maximum power level of approximately 1 mW. Security features include access control and encryption based on the advanced encryption standard (AES). ZigBee is theoretically scalable up to 65,536 devices.The term ZigBee refers to the technique, known as the ZigBee principle, that a domestic honeybee uses to communicate the location of a new food source to other members of the colony. See also ad hoc, AES, BPSK, CSMA/CA, DSSS, frequency band, ISM, MAC, mesh topology, peer-to-peer, propagation, QPSK, star topology, WPAN, ZC, ZED, ZigBee principle, and ZR.

ZMODEM - A public domain file transfer protocol used in asynchronous data communications. ZMODEM offers a number of improvements to the earlier XMODEM protocol, including an expanded 32-bit cyclic redundancy check (CRC) for purposes of improved error control. ZMODEM also supports larger block sizes (512 bytes), allows a transmission to resume where it left off in the event of a communications failure, and reduces latency through a sliding window protocol that allows a modem to transfer a series of blocks without waiting for individual acknowledgements from the receiving modem. ZMODEM was developed by Chuck Forsberg in 1986 for use in the Telenet X.25 network, and quickly became popular in the bulletin board system (BBS) community for file downloads. See also asynchronous, BBS, block, CRC, error control, Kermit, modem, X.25, XMODEM, and YMODEM.

Zulu Time - Formerly known as Greenwich Mean Time. Time that is kept on an atomic 24-hour clock in France. The Zulu time standard is now more accurate by innovation of the cesium timing reference standard, which is the time-keeping element in “bits clocks” (timing devices used in central office nodes to synchronize SONET equipment). Zulu time is slang for Universal Time Coordinated.

ZWPF (Zero-Water-Peak Fiber) - Single-mode fiber (SMF) manufactured without hydroxyl (OH) ion contamination in order eliminate the attenuation peak in the 1400 nm window, which is in the Eband (1360–1460 nm). The traditional SMF manufacturing process introduces hydroxyl (OH) ions into the fiber core. Wavelengths in the region around 1400 nm attenuate about 2 dB/km as a result of their interaction with those ions. As traditional single-wavelength fiber optic transmission systems (FOTS) employing SMF operate in the 1310 nm or 1550 nm window, water peak attenuation does not affect them. However, 4 of the 18 channels in coarse wavelength division multiplexing (CWDM) systems fall within the E-band and, therefore, are rendered unusable by water peak attenuation. Low–water-peak fiber (LWPF) has low levels of hydroxyl ion contamination and, therefore, suffers low water peak attenuation. ZWPF is the contemporary industry standard for all SMF. See also attenuation, CWDM, dB, dB/km, E-band, FOTS, hydroxyl, LWPF, SMF, water peak, wavelength, and window.