Telecom Dictionary - Definitions of terms

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Z

Z - Z is an abbreviation for Zulu time. See Coordinated Universal Time. - Time scale based on the second (SI), as defined and recommended by the CCIR, and maintained by the Bureau International des Poids et Mesures (BIPM). For most practical purposes associated with the Radio Regulations, UTC is equivalent to mean solar time at the prime meridian (0° longitude), formerly expressed in GMT. Note 1: The maintenance by BIPM includes coordinating inputs from time standards belonging to various national laboratories around the world, which inputs are averaged to create the international time standard (second). Note 2: The full definition of UTC is contained in CCIR Recommendation 460-4. Note 3: The second was formerly defined in terms of astronomical phenomena. When this practice was abandoned in order to take advantage of atomic resonance phenomena (" atomic time ") to define the second more precisely, it became necessary to make occasional adjustments in the "atomic" time scale to coordinate it with the workaday mean solar time scale, UT-1, which is based on the somewhat irregular rotation of the Earth. Rotational irregularities usually result in a net decrease in the Earth's average rotational velocity, and ensuing lags of UT-1 with respect to UTC. Note 4: Adjustments to the atomic, i.e., UTC, time scale consist of an occasional addition or deletion of one full second, which is called a leap second. Twice yearly, during the last minute of the day of June 30 and December 31, Universal Time, adjustments may be made to ensure that the accumulated difference between UTC and UT-1 will not exceed 0.9 s before the next scheduled adjustment. Historically, adjustments, when necessary, have usually consisted of adding an extra second to the UTC time scale in order to allow the rotation of the Earth to "catch up." Therefore, the last minute of the UTC time scale, on the day when an adjustment is made, will have 61 seconds. Synonyms World Time, Z Time, Zulu Time.

ZBTSI (zero-byte time slot interchange) - A technique applied to a DS1 frame to ensure pulse density requirements are met, where bits 2 through 193 of each frame are scrambled to minimize the occurrence of all-zero octets. When an all-zero octet is contiguous to another octet with zeros and they would combine to violate the ones density requirement, an algorithm is invoked where some all-zero octets are replaced by an address chain. The reverse algorithms are performed by the receiving terminal.

Zero-bit Insertion - A bit-stuffing technique used with bit-oriented protocols to ensure that six consecutive "1" bits never appear between the two flags that define the beginning and the ending of a transmission frame. Note: When five consecutive "1" bits occur in any part of the frame other than the beginning and ending flag, the sending station inserts an extra "0" bit. When the receiving station detects five "1" bits followed by a "0" bit, it removes the extra "0" bit, thereby restoring the bit stream to its original value. Synonyms zero insertion, zero stuffing.

Zero dBm Transmission Level Point (0 dBm TLP) - In a communication system, a point at which the reference level is 1 mW, i.e., 0 dBm. Note: The actual power level of the communications traffic is not necessarily 0 dBm. It is usually below the reference level. The reference is for system design and test purposes. Synonym zero transmission level point.

Zero-Dispersion Slope - In a single-mode optical fiber, the rate of change of dispersion, with respect to wavelength, at the fiber's zero-dispersion wavelength. Note 1: In silica-based optical fibers, the zero-dispersion wavelength occurs at approximately 1.3 m, but this wavelength may be shifted toward the minimum-loss window by the addition of dopants to the fiber material during manufacture. Note 2: Doubly and quadruply clad single-mode fibers have two zero-dispersion points, and thus two zero-dispersion slopes.

Zero-Dispersion Wavelength = 1. In a single-mode optical fiber, the wavelength or wavelengths at which material dispersion and waveguide dispersion cancel one another. Note: In all silica-based optical fibers, minimum material dispersion occurs naturally at a wavelength of approximately 1.3 m. Single-mode fibers may be made of silica-based glasses containing dopants that shift the material-dispersion wavelength, and thus, the zero-dispersion wavelength, toward the minimum-loss window at approximately 1.55 m. The engineering tradeoff is a slight increase in the minimum attenuation coefficient. 2. Loosely, in a multimode optical fiber, the wavelength at which material dispersion is minimum, i.e., essentially zero. Synonym minimum-dispersion wavelength.

Aero Dispersion Window - Synonym minimum-dispersion window.

Zerofill - To fill unused storage locations in an information system (IS) with the representation of the character denoting "0".

Zero Insertion - See zero-bit insertion. A bit-stuffing technique used with bit-oriented protocols to ensure that six consecutive "1" bits never appear between the two flags that define the beginning and the ending of a transmission frame. Note: When five consecutive "1" bits occur in any part of the frame other than the beginning and ending flag, the sending station inserts an extra "0" bit. When the receiving station detects five "1" bits followed by a "0" bit, it removes the extra "0" bit, thereby restoring the bit stream to its original value.

Zeroize - To remove or eliminate the key from a crypto-equipment or fill device.

Zeroized - Electronically stored data that have been degaussed, erased, or overwritten.

Zero-Level Decoder - A decoder that yields an analog level of 0 dBm at its output when the input is the digital milliwatt signal. Note: The signal is a 1-kHz sine wave.

0 + (7 or 10 digits) = A feature of the North American Numbering Plan that identifies customer dialed calls that are operator assisted, either by electronic or manual (human) means.

Zero Stuffing - See zero-bit insertion. A bit-stuffing technique used with bit-oriented protocols to ensure that six consecutive "1" bits never appear between the two flags that define the beginning and the ending of a transmission frame. Note: When five consecutive "1" bits occur in any part of the frame other than the beginning and ending flag, the sending station inserts an extra "0" bit. When the receiving station detects five "1" bits followed by a "0" bit, it removes the extra "0" bit, thereby restoring the bit stream to its original value.

Zero Suppression - The elimination of nonsignificant zeros from a numeral.

ZTLP - Abbreviation for zero transmission level point.

Zero Transmission Level P oint (0TLP) - Synonym zero dBm transmission level point. - In a communication system, a point at which the reference level is 1 mW, i.e., 0 dBm. Note: The actual power level of the communications traffic is not necessarily 0 dBm. It is usually below the reference level. The reference is for system design and test purposes. Synonym zero transmission level point.

Zip-cord - In optical communications, a two-fiber cable consisting essentially of two single-fiber cables having their jackets conjoined by a strip of jacket material. Note 1: This name is borrowed from electrical terminology referring to lamp cord. As with lamp cord, optical zip-cord may be easily furcated by slitting or tearing the two jackets apart, permitting the installation of optical connectors. Note 2: Zip-cord cables include both loose-buffer and tight-buffer designs.

Zone - See communications zone, Fresnel zone, skip zone.

Zone of Influence - The area surrounding a power station that is raised in potential above a remote or true grounding (earthing) point.

Zone of Protection - The space, adjacent to a lightning protection system, that is substantially immune to direct lightning strokes.

Zone of Silence - Synonym skip zone.

Zooming- The act of changing the scale of a display, generally without changing the amount of screen space it occupies.

Z Time - Abbreviation for Zulu Time. See Coordinated Universal Time.

Zulu Time (Z) - Synonym Coordinated Universal Time. Formerly a synonym for Greenwich Mean Time.

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