Datacom Glossary Alien Crosstalk (AXT): Unwanted signal coupling from one component, channel, or permanent link to another is defined as alien crosstalk. Alien crosstalk is only specified by the Standards as a power sum parameter for components and cabling to approximate the energy present when all pairs are energized. Power sum alien measured at the near- end is called Power Sum Alien Near-End Crosstalk loss (PSANEXT) and power sum alien crosstalk at the far-end is called Power Sum Alien Attenuation to Crosstalk Ratio, far-end (PSAACRF). High power sum alien crosstalk levels can compromise the operation of 10G Base-T applications. American Wire Gauge (AWG): A system used to specify wire size. The greater the wire diameter, the smaller the value (e.g., 24 AWG [0.51 mm {0.020 in}]). Asynchronous Transfer Mode (ATM): A high-speed switching transmission protocol that utilizes payload packages organized into 53-byte cells to carry data. Attenuation: The decrease in magnitude of transmission signal strength between points, expressed as the ratio of output to input. Measured in dB, usually at a specific frequency for copper or wavelength for optical fiber, the signal strength may be power or voltage. Attenuation-to-Crosstalk Ratio (ACR): The difference between attenuation and crosstalk, measured in dB at a given frequency. This difference is critical to ensure that the signal sent down the twisted-pair cable is stronger at the receiving end of the cable than any interference signals (crosstalk) from other cable pairs. Attenuation-to-Crosstalk Ratio, Far-End (ACRF), formerly ELFEXT: A measure of the unwanted signal coupling from a transmitter at the near-end into another pair measured at the far-end, and relative to the received signal level. Bandwidth: A range of frequencies, usually the difference between the upper and lower limits of the range, expressed in Hz. It is used to denote the potential capacity of the medium, device or system. In copper and optical fiber cabling, the bandwidth decreases with increasing length. Baseband transmission: A transmission technique in which all of the available bandwidth is dedicated to a single communications channel. Only a single message transfer can occur at a given time. Bit Error Rate (BER): The ratio of incorrectly transmitted bits to total transmitted bits. A primary specification for all transmission systems, it is usually expressed as a power of 10. The number of errors made in a digital transmission as compared to complete accuracy. Broadband transmission: The transmission of multiple signals on a medium at the same time, sharing the entire bandwidth of the medium. The signals are multiplexed into channels with a bandwidth of 6 kHz each and occupy a different frequency on the cable. The signals are divided, usually by frequency divisions, to allow more than one channel on the cable at any time. Broadcast: A technique for sending data simultaneously to all devices attached to a network with a single transmission. See multicast and unicast. Capacitance: The tendency of an electronic component to store electrical energy. Pairs of wire in a cable tend to act as a capacitor. The charge on one of two conductors of a capacitor divided by the potential difference between them (measured in farads). Common-mode noise (and longitudinal): The noise voltage that appears between each signal conductor to ground, caused by electrostatic induction and/or electromagnetic induction. Cross-connect: A facility enabling the termination of cable elements and their interconnection or cross-connection. Crosstalk: The unwanted reception of electromagnetic signals on a communications circuit from another circuit. Decibel (dB): A logarithmic unit used for expressing the loss or gain of signal strength. One dB is the amount by which the pressure of a pure sine wave of sound must be varied in order for the change to be detected by the average human ear. Delay skew: The difference in the propagation delay between any two pairs within the same cable sheath. Dielectric constant: The ratio of capacitance of an insulated wire measured against the same wire uninsulated, but using air as the dielectric, which is equal to one. Elongation: The fraction increase in the length of a material stressed in tension. Equal Level Far-End Crosstalk (ELFEXT): A measure of the unwanted signal coupling from a transmitter at the near end into another pair measured at the far end, relative to the received signal level. Equal Level Transverse Conversion Transfer Loss (ELTCTL): A calculation, expressed in dB, of the difference between measured TCTL and the differential mode insertion loss of the disturbed pair. Ethernet: A LAN protocol using a logical bus structure and carrier sense multiple access with collision detection. Far-end crosstalk loss: A measure of the unwanted signal coupling from a transmitter at the near end into another pair measured at the far end, relative to the transmitted signal level. FEP: Fluorinated Ethylene Propylene Frequency: The measure of the number of cycles (waves) per second, expressed in Hz. Full Duplex: Simultaneous two-way transmission utilizing all 4 pairs. Gigabits per second (Gb/s): A transmission rate denoting one billion bits per second. Gigabit Ethernet: A carrier sense multiple access with collision detection LAN standard developed by the IEEE 802 group operating at one Gb/s. Hertz (Hz): A unit of frequency equal to one cycle per second. Insertion loss: The signal loss resulting from the insertion of a component, link or channel between a transmitter and receiver (often referred to as attenuation). Insulation: The dielectric material that physically separates wires and prevents conduction between them. Longitudinal Conversion Loss (LCL): A measure of how well a pair is balanced and a useful metric of a cable’s ability to reject noise from external sources and to limit electromagnetic radiation from the cable to the environment. Examples of external noise sources include noisy power lines, electrical equipment, walkie-talkies, radio and radar stations, and alien crosstalk from other telecommunications cables. As structured cabling is applied to industrial environments and network speeds increase, balance becomes increasingly important. Technical Information 82
