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

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Jabber - In local area networks, transmission by a data station beyond the time interval allowed by the protocol.

Jack - 1. A female fitting or connector that accepts a male mating component ("plug") to facilitate an electrical connection. Note: The term jack is frequently applied in applications involving communications signals, while the term receptacle is almost universally reserved for applications involving the distribution of electric power. 2. An analogous fitting or connector used to facilitate an optical fiber connection. See RJ-11 , RJ-14. and modular connector.

Jacket - Synonym sheath. Of a communications or power cable, the outer covering or coverings of tough material, often plastic, that is resistant to environmental hazards such as abrasion, liquid intrusion, solar radiation, etc., and is used to protect cable component (s) such as optical fibers or metallic conductors that transport the signal or power. Note: There may be more than one sheath surrounding a given cable. For example, some cable designs use an inner sheath surrounded by metallic armor, over which is an outer sheath.

Jamming - The deliberate radiation, reradiation, or reflection of electromagnetic energy for the purpose of disrupting enemy use of electronic devices, equipment, or systems.

Jamming Margin - The level of interference (jamming) that a system is able to accept and still maintain a specified level of performance, such as maintain a specified bit-error ratio even though the signal-to-noise ratio is decreasing.

Jamming to Signal Ratio (J/S) - The ratio, usually expressed in dB, of the power of a jamming signal to that of a desired signal at a given point such as the antenna terminals of a receiver.

Jam Signal - A signal that carries a bit pattern sent by a data station to inform the other stations that they must not transmit. Note 1: In carrier-sense multiple access with collision detection (CSMA/CD) networks, the jam signal indicates that a collision has occurred. Note 2: In carrier-sense multiple access with collision avoidance (CSMA/CA) networks, the jam signal indicates that the sending station intends to transmit. Note 3: "Jam signal" should not be confused with " electronic jamming."

Java^TM - A trademarked set of programming language technologies for creating and safely running software programs in both stand-alone and networked environments. Most graphics-based Web browsers can recognize and run Java codes.

Java Applet - A small application-program component that typically executes in a client's Web browser, but can execute in a variety of other simple applications or devices; Java applets support the applet programming model and may be downloaded through the Internet via a Web site and run directly on a remote computer; Java applets are often used to create Web page effects.

JavaBean - A portable, platform-independent, reusable component model that conforms to specification defining how Java objects interact.

Java Database Connectivity (JDBC^TM) - An industry standard for database-independent connectivity between a computer platform or device operating in the JavaTM environment and a wide range of databases; the JDBC TM provides a call-level API (application program interface) for SQL-based (structured-query-language based) database access.

JDBC - Abbreviation for Java database connectivity.

Jerkiness - In a video display, the perception, by human vision faculties, of originally continuous motion as a sequence of distinct "snapshots." Note 1: The perception of continuous motion by human vision faculties is a manifestation of complex functions, i.e., characteristics, of the eyes and brain. When presented with a sequence of fixed, i.e., still, images of sufficient continuity and at a sufficiently frequent update rate, the brain interpolates intermediate images, and the observer subjectively appears to see continuous motion that in reality does not exist. Note 2: For example, the update rate of NTSC television displays is 30 frames (60 fields) per second.

jfif or .jfif - A file-name extension that identifies an image file compressed with the Joint Photographic Experts Group (JPEG) format.

Jini ^TM - A set of Java application program interfaces (APIs) to enable transparent networking of devices and services, thus eliminating the need for system or network administration intervention by a user.

Jitter - 1. Abrupt and unwanted variations of one or more signal characteristics, such as the interval between successive pulses, the amplitude of successive cycles, or the frequency or phase of successive cycles. Note 1: Jitter must be specified in qualitative terms (e.g., amplitude, phase, pulse width or pulse position) and in quantitative terms (e.g., average, RMS, or peak-to-peak). Note 2: The low-frequency cutoff for jitter is usually specified at 1 Hz. 2. Random variability of data pass-through time. See timing jitter.

Job - In computing, a unit of work that is defined by a user and that is to be accomplished by a computer. Note: A job is identified by a label and usually includes a set of computer programs, files, and control statements to the computer operating system.

Job-Recovery Control File - Synonym backup file. A copy of a file made for purposes of later reconstruction of the file, if necessary. Note: A backup file may be used for preserving the integrity of the original file and may be recorded on any suitable medium.

Johnson Noise - Synonym thermal noise. The noise generated by thermal agitation of electrons in a conductor. The noise power, P, in watts, is given by P = kT f, where k is Boltzmann's constant in joules per kelvin, T is the conductor temperature in kelvins, and f is the bandwidth in hertz. Note 1: Thermal noise power, per hertz, is equal throughout the frequency spectrum, depending only on k and T. Note 2: For the general case, the above definition may be held to apply to charge carriers in any type of conducting medium.

Joint - For optical fibers, a splice or connector.

Joint Multichannel Trunking and Switching System - That composite multichannel trunking and switching system formed from assets of the Services, the Defense Communications System, other available systems, and/or assets controlled by the Joint Chiefs of Staff to provide an operationally responsive, survivable communication system, preferably in a mobile/transportable/recoverable configuration, for the joint force commander in an area of operations.

Joint Random Buried Plant - Telecommunications outside plant that is directly buried in the same trench with power conductors, with no restriction regarding minimum separation between the two systems.

Joint Telecommunications Resources Board (JTRB) - The body required to be established by Section 2(b) (3) of Executive Order No. 12472 to assist the Director of the Office of Science and Technology Policy in the exercise of assigned nonwartime emergency telecommunications functions.

Joint Use Aerial Plant - Aerial telecommunications and power plant utilizing the same structure, such as poles.

Journal - 1. A chronological record of data processing operations that may be used to reconstruct a previous or an updated version of a file. Synonym log. 2. In database management systems, the record of all stored data items that have values changed as a result of processing and manipulation of the data.

Joy Stick - In computer graphics, a lever (with at least two degrees of freedom) that is used as an input unit, normally as a locator.

J-PEG [ or JPEG] - Abbreviation for Joint Photographic Experts Group. 1. A standardized, if relatively lossy, file format for transporting, storing, and/or displaying data representing still images and graphical data. Note: Along with .gif, it is one of the most common ways that photos are moved over the Web. 2. Images compressed with the JPEG format and identified with the .jpg or .jpeg file-name extension. 3. An international standards group functioning under ISO and IEC developing an international consensus on an image compression algorithm for continuous-tone still color pictures.

Judder - A temporal artifact associated with moving images, which artifact occurs when the image is sampled at one frame rate and converted to a different frame rate for display; as a result, motion vectors in the display may appear to represent continuously varying velocities. Note: The subjective effect of the artifact becomes more obvious when the frame-rate conversion is made by simple deletions or repetitions of selected frames (or fields). It may become less obvious when interpolated frames (or fields) are generated by using predictive algorithms.

Julian Date - 1. The sequential day count reckoned consecutively beginning January 1, 4713 B.C. Note: The Julian date on January 1, 1990, was 2,446,892. 2. The sequential day count of the days of a year, reckoned consecutively from the first day of January. Note: In modern times, the definition of Julian date has been corrupted to use the first day of the year as the point of reference. To avoid ambiguity with the traditional meaning, "day of year" rather than "Julian date" should be used for this purpose.

Jumper - Synonym cross-connection. Connections between terminal blocks on the two sides of a distribution frame, or between terminals on a terminal block. Note: Connections between terminals on the same block are also called straps.

Junction Point - Synonym node. 1. In network topology, a terminal of any branch of a network or an interconnection common to two or more branches of a network. Synonyms junction point, nodal point. 2. In a switched network, one of the switches forming the network backbone. Note: A node may also include patching and control facilities. 3. A technical control facility (TCF). 4. A point in a standing or stationary wave at which the amplitude is a minimum. In this sense, synonym null.

Jurisdiction - 1. In telecommunications, the functional separation of telecommunications networks. A jurisdiction is one of the following four types: (a) local exchange carrier network; (b) interexchange carrier network; (c) end user network; (d) some combination of the above. 2. Loosely, and in a more general sense, the regulatory authority of the Federal Communications Commission as specified in the Communications Act of 1934, supplements thereto, and numerous court decisions; and the regulatory authority of state regulatory commissions as specified in the laws established by each state.

Justification - The process of changing the digit rate of a digital signal in a controlled manner so that it is in accord with a digit rate different from its own inherent rate, usually without loss of information. Synonyms [loosely] bit stuffing, de-stuffing, justify.

Justify - 1. To shift the contents of a register or a field so that the significant character at the specified end of the data is at a particular position. 2. To align text horizontally or vertically so that the first and last characters of every line, or the first and last line of the text, are aligned with their corresponding margins. Note 1: In English, text may be justified left, right, or both. Left justification is the most common. Note 2: The last line of a paragraph is usually only left justified. 3. To align data on a designated character position.

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