K

K band - The portion of the microwave radio spectrum in the range of 10.9–36.0 GHz, as specified by the ITU-R.The K band is subdivided into Ku band and Ka band. Ku band is so called as it is under the center of the K band, and Ka band is so called as it is above the center of the K band.Applications include satellite and terrestrial microwave systems. See also electromagnetic spectrum, ITU-R, microwave, and satellite.

k - 1. kilo (k). From Greek khilioi, meaning thousand. 2. In transmission systems, kHz (kiloHertz) is a thousand (10 ³ ) Hertz, kbps (kilobit per second) is a thousand (10 ³ ) bits per second, and km is a thousand (10 ³ ) meters. In transmission systems, therefore, a thousand is exactly 1,000, since the measurement is based on a base 10, or decimal, number system. 3. In computing and storage systems, a kB (kiloByte) is actually 1,024 (2 ¹⁰ ) bytes, since the measurement is based on a base 2, or binary, number system.The term kB comes from the fact that 1,024 is nominally, or approximately, 1,000. So, 64 kB of memory is actually 65,536 (2 ¹⁶ ) bytes. 4. The only letter worth five points in the American version of Scrabble, the popular board game.

K - The symbol for Kelvin, the SI unit of absolute temperature. Measured from absolute zero, zero (0) degrees Kelvin (K) = –273.16 degrees Celsius (C). The formula for converting Kelvin to Celsius is Kelvin (K) = Celsius (C) + 273.16. See also SI.

Ka band - The portion of the microwave radio spectrum in the range of 20.0–30.0 GHz, as specified by the ITU-R.The K band is subdivided into Ku band and Ka band. Ka-band is so called as it is above the center of the K band. Applications include satellite microwave systems, with current emphasis on mobile voice and data. See also electromagnetic spectrum, ITU-R, K band, Ku band, microwave, and satellite.

Kao, Charles - While engineers at Standard Telecommunications Laboratories, an ITT subsidiary, Charles Kao and George Hockham achieved the first conceptual breakthrough in the development of fiber optic transmission systems (FOTS). In 1966, Kao and Hockham determined that optical fibers of fused silica could satisfy signal attenuation requirements by overcoming issues of absorption, diffusion, and bending loss. At the time, attenuation of 20 dB per kilometer was considered satisfactory for a commercially viable system. Contemporary FOTS are designed around attenuation levels in the range of 1.5–3.0 db per kilometer, or so, depending on the specific type of fiber and the wavelength employed. See also FOTS and optical fiber.

kB (kilobyte) - One thousand bytes. In computing and storage systems, a kB (kiloByte) is actually 1,024 (2 ¹⁰ ) bytes, since the measurement is based on a base 2, or binary, number system.The term kB comes from the fact that 1,024 is nominally, or approximately, 1,000. See also byte and k.

kbps (kilobit per second) - One thousand (10 ³ ) bits per second. A measure of bandwidth in a digital transmission system. See also bandwidth, bps, and k.

keep alive bits - In the event that a digital circuit is silent, i.e. there is no active data transmission, the channel service unit (CSU) that interfaces the circuit to the customer’s data communications equipment (DCE) will regularly transmit a one (1) bit, collectively known as keep alive bits, to ensure that there are electrical pulses on the circuit with at least a minimal density.This process ensures that the various circuit terminating equipment and repeaters remain synchronized and, in some cases, powered. See also CSU, DCE, ones density, repeater, and synchronize.

Kelvin (K) - See K.

Kerberos - Authorization software that makes use of private-key authentication. Developed by the Massachusetts Institute of Technology (MIT), Kerberos is available for free, although commercial versions exist. Kerberos was named for the three-headed dog, also known as Cerberus, that guarded the gates of Hades in Greek mythology. Note:Although, according to Greek legend, Hercules defeated Kerberos, a hacker of Herculean proportions has yet to emerge victorious over this powerful security software. See also Access Manager, authorization, security, and Sesame.

Kermit - 1. Kermit the Frog.The green frog puppet star of The Muppet Show. 2. An asynchronous file transfer protocol that organizes data into 128-byte blocks and employs a cyclic redundancy check (CRC) for excellent error control. Kermit operates over a wide variety of connections, including dial-up modem connections and TCP/IP connections. Although Kermit is not in the public domain, Columbia University generally allows its use at no charge, so most communications protocols support it. Kermit was developed by the Columbia University Computer center in 1981 and named for Kermit the Frog. See also asynchronous, block, CRC, protocol, XMODEM, and ZMODEM.

kernel - The core of a computer operating system (OS).The kernel resides in memory and performs basic tasks such as managing internal memory, input and output operations, and peripheral devices.A kernel also is responsible for launching applications and allocating associated system resources such as processor time. See also OS.

KEVLAR® - The registered name under which Dupont markets aramid fiber. See also aramid.

key service unit (KSU) - See KSU.

key telephone system (KTS) - See KTS.

key - 1. A small mechanical device for opening, closing, or switching electrical circuits. A telegraph key, for example, is used to open and close an electrical circuit to send short and long pulses of electric current. See also keyboard, keypad, and KTS. 2. A string of bits used for encrypting and decrypting information.A private key is known to only one person, typically the sender.A public key is known to more than one person, typically both the sender and the receiver, and is published and freely available from a public key infrastructure (PKI) or certificate authority (CA). See also CA, encryption, PKI, private key encryption, and public key encryption.

keyboard - A simple computer input device comprising a set of alphabetic, numeric, punctuation, symbol, control, and function keys mounted on a board or other flat surface or control panel.When the user depresses a key or a combination of keys, a coded signal is sent to the computer. If the key is associated with a character, the computer echoes the signal by displaying the character on the monitor. See also keypad.

keypad - A simple input device comprising a set of keys or buttons mounted on a keyboard or control panel associated with a computer, telephone, microwave oven, or other device or on a remote control device. See also keyboard.

kHz (kiloHertz) - One thousand (10 ³ ) Hertz. A measure of bandwidth in an analog transmission system. See also bandwidth, Hertz, and k.

kilo- (k) - See k.

kilobit per second (kbps) - See kbps.

kiloByte (kB) - See kB.

kiloHertz (kHz) - See kHz.

kilometer (km) - See km.

Kingsbury Commitment - The commitment, expressed in a letter written by Nathan C. Kingsbury, an AT&T vice-president, to the United States Attorney General in December 1913, to resolve a number of antitrust issues. Kingsbury committed AT&T to dispose of its holdings in Western Union, to purchase no more independent (i.e., non-Bell) telephone companies without the approval of the Interstate Commerce Commission (ICC), and to make interconnection with the independent telephone companies. Eventually, national standards were established to govern the nature and rules of interconnection.The ITU-T governs interconnection at the international level. See also AT&T, ITU-T, and Western Union.

km (kilometer) One thousand (10 ³ , or 1,000) meters. See also k and meter.

knife-edge diffraction - The phenomenon by which an electromagnetic waveform diffracts, or bends, as it strikes the sharp edge of an obstacle transverse to its direction of propagation.The portion of the signal that is not cut off by the knife edge continues to propagate, but the edge of the signal bends into the line-of-sight (LOS) shadow region as if to fill the void left by the portion of the signal cut off. Knife-edge diffraction can be used to advantage in radio communications when line-of-sight (LOS) cannot be achieved due to the presence of an obstacle, such as a mountaintop or building, that lies in the path of the transmit and receive antennas. See also diffraction and LOS.

KSU (Key Service Unit) - The common control unit of a key telephone system (KTS).The KSU stores programmed features, which are served to individual users and stations based on their individual access privileges.

KTS (Key Telephone System) - A voice-optimized telecommunications system designed for small business or small office applications (see Figure K-1), typically defined as involving no more than 50 stations.The term key refers to the buttons that mechanically opened and closed the line circuits on the early generation of KTSs. Although the buttons are no longer mechanical keys, KTSs remain relatively simple CPE systems that allow multiple station users to share a number of outside lines that the users select by depressing the button associated with the specific circuits they desire to access.This approach is unlike that of a PBX switch, which has the intelligence to accept a call request from a user station, determine the most appropriate circuit from a shared pool of circuits, and set up the connection through common switching equipment. Most small KTSs are squared, meaning that every key set is configured alike, with every outside line appearing on every set. Thereby, every station user can access every outside line for both incoming and outgoing calls, and all feature presentations are consistent. In larger systems, the physical size of the telephone sets required to maintain the squaring convention would be impractical, but departmental subgroups often are squared. All but the simplest key systems have a software-based common control unit, known as a Key Service Unit (KSU), where programmed features are stored and provided to individual users and stations based on their individual access privileges. Introduced in 1938, early electromechanical KTS systems (1A, 1A1, and 1A2) were limited in feature content to hold, intercom, speakerphones, and auto dialers. Electronic KTS (EKTS) systems appeared in the 1970s, offering many of the same features as PBX systems. Most contemporary key systems are hybrids, meaning that they can operate either as a KTS or a PBX. Hybrids generally are limited to 200–250 or so ports, each of which often can serve to connect end user terminal equipment or an outside line to the KSU. See also 1A, 1A1, 1A2, CPE, line, PBX, and trunk.

Ku band - The portion of the microwave radio spectrum in the range of 12.0–18.0 GHz, as specified by the ITU-R.The K band is subdivided into Ku band and Ka band. Ku band is so called as it is under the center of the K band. Applications include satellite and terrestrial microwave systems. See also electromagnetic spectrum, ITU-R, K band, Ka band, microwave, and satellite.