GLOSSARY

ACR - Attenuation to Crosstalk Ratio. Measured in dB (decibels). High values are desired. The usable bandwidth at any given frequency ("10 dB ACR at 100 MHz") within the range a cable is rated. On a graph of decibels (dB) vs. frequency (MHz), showing plotted performance curves for attenuation and crosstalk, ACR is the distance between these two curves. The object in cable construction is to increase usable bandwidth at all frequencies at which a cable may be used. Performance above a cable's rating (above 100 MHz for CAT5) is usually unimportant.

ATM - Asynchronous Transfer Mode. Transfers data in "packets", a system that allows for multiple uses simultaneously and is always turned on. ATM allows network connections up to 100 times faster than today's 56.6 kilobit per second dialup modem.

ATTENUATION - Signal power loss in optical fiber or UTP. Measured in dB (decibels). Low values are desired. Attenuation increases with frequency and temperature. Full power is defined as "0dB" and half power as "-3dB". A "-0.5dB attenuation" means that 10% of the transmitted power is lost. A "-20.0dB attenuation" means that 99% of transmitted power has been lost.

BACKBONE - Fiber optic providers. The part of a communications network that handles the major traffic. It may interconnect multiple locations, and smaller networks may be connected to it.

BANDWIDTH - First interpretation: Transmission capacity of a computer channel, communications line or bus. It is expressed in cycles per second (Hertz or Hz), the bandwidth being the difference between the lowest and highest frequencies transmitted. The frequency is equal to or greater than the bits per second. Bandwidth is also often stated in bits or bytes per second. Also See Video Bandwidth and second interpretation.

BANDWIDTH - Second interpretation: Bandwidth is fixed, frequency changes. A data stream of ones and zeroes creates frequency and is never the same as it changes with the data. If we were to consistently transmit one million bits of data per second, our bandwidth would be a constant at 1 Mbps. To do this, a maximum of one million bi-polar cycles per second would be required. This is the carrier frequency required to transmit a given number of bits within a given amount of time. Groupings of ones or zeroes cause "NRZ" (non-return to zero); changing from one or more ones to one or more zeroes causes the bi-polar effect (a cycle). Alternating single ones and zeroes would create the highest frequency, one million cycles per second ( 1 MHz ). If a half million ones were grouped together followed by a half million zeroes, this would represent one cycle per second. Since data makes frequency happen, our frequency will be a variable ( between 1 MHz and 1 Hz ). Also See Video Bandwidth and first interpretation.

BEND RADIUS - Minimum radius for cable. Minimum radius for optimum performance. Usually specified by cable manufacturers. For optical fiber, "no tighter than a coffee cup" (light will not stay in fiber).

CAT3 - Category 3, a standard. UTP cable and hardware must be able to maintain a transmission rate of 16 MHz. This was the standard for UTP performance as late as 1988.

CAT4 - Category 4, a standard. UTP cable and hardware must be able to maintain a transmission rate of 20 MHz.

CAT5 - Category 5, a standard. UTP cable and hardware must be able to maintain a transmission rate of 100 MHz. This standard for UTP performance was created in 1992. Most CAT5 cable is used in 10BaseT applications. CAT5 performance is only possible when cable, connector modules, patch cords, and all electronics carry the same CAT5 rating.

CAT5e - Category 5e, a standard. A more demanding level of cable performance above CAT5.

CAT6 - Category 6, a standard. Categories 6, 6e, and 7 represent the latest technological capabilities of UTP cable and equipment manufacturing.

DARK FIBER - Optical fiber before connection to equipment. After optical fiber is terminated and connected to telecommunications equipment, it has been "lighted-up".

DELAY SKEW - UTP cable performance. Difference in signal arrival between fastest and slowest pairs. Since wire size is uniform among all pairs in a cable, velocity of propagation causes signals to travel at the same rate along the wire. Pairs with higher twist rates use greater lengths of wire. In CAT5 cable, the standard is 45 nanoseconds between the fastest (shortest) and slowest (longest) pairs.

DISPERSION - Spreading of light as it travels through cable. As light pulses along optical fiber, bending of the cable changes the end of the pulse. The pulse-end becomes fuzzy, is not clearly recognized, and causes the bit error rate to increase.

DWDM - Dense Wave Division Multiplexing. Sends multiple frequencies of light down same fiber at same time. It is now possible to increase fiber capability by a factor of 32. In several years, capacities of 100-fold or more may be possible.

FIBER RING - A network of optical fiber cable. Cables containing 4, 6, 12, 24, or more strands of optical fiber serve a full range of telecommunication needs of customers along the cable's route. As more customers are added, more and larger cables are installed. Such cables are connected to high-speed digital networks provided by regional or national ISPs.

FIBER SPLICING - Preparing optical fiber strands for use. Before single-mode fiber can be used (in long-haul applications or between buildings in a fiber ring), each strand must be connected to another. Used outdoors or in unheated areas. The best method is a crimp splice using 3M's patented Fibrlok technology.

FIBER TERMINATION - Preparing optical fiber strands for use. Before multi-mode dark fiber can be used (in an office or school), each strand must be securely mounted in a connector. Used indoors or in temperature-controlled areas. Popular termination methods are anaerobic, epoxy, and hot-melt. Older methods terminate one strand into one connector. Newer methods terminate two strands at the same time.

FIBER OPTIC - Optical Fiber. Thin glass wire designed for light transmission, capable of transmitting billions of bits per second. Unlike electrical pulses, light pulses are not affected by random radiation in the environment. Each hair-thin optical fiber can carry thousands of digitized voice conversations at the same time. Also See single-mode, multi-mode.

FIBER TESTING - Verify performance of each strand. After optical fiber is installed, terminated and/or spliced, each strand is tested. Low dB test results indicate that the strand is undamaged and that each splice and termination has been done correctly. Printed documentation verifies successful, passed tests.

ION - Integrated On-Demand Network. Possibly available to small businesses and residential customers by Winter, 1999. Uses asynchronous transfer mode (ATM) technology. Capacities to 620 mbps.

ISP - Internet Service Provider. An ISP can be very small, serving only a few towns, or very large, serving users all over the USA and abroad. First level ISPs use their own high-speed fiber networks. Second level ISPs usually buy access to backbone providers or first level ISPs.

PHOTONICS - A branch of physics. Now, information travels on fiber optic cables in form of laser generated light. Photonics studies ways of manipulating light waves to increase fiber transmission capabilities.

MICRON - One millionth of a meter. Approximately 1/25,000 of an inch. One micron is as high as a fingerprint (the oil residue of your finger tip).

MULTI-MODE - Optical Fiber. A strand of fiber usually has: 62.5 micron diameter glass fiber core; 125 micron diameter cladding; a coating (brown or clear); and an outer buffer (one of 12 fiber color codes). Used in short-haul applications where cable is likely to be bent, such as in LANs or inside buildings, walls, and conduit. Light bounces through the fiber core being reflected off the cladding.

NEXT - Near End Cross Talk. An indicator of signal coupling in UTP cable. Expressed in dB - higher values are desired. NEXT increases with frequency and is effected by cable construction and installation quality.

PAIR-TO-PAIR - Testing CAT5, CAT6 cable. An older method of performance testing. Measures one twisted pair against another pair in the cable (P1-P2, P1-P3, etc.).

POP - Point of Presence. An access point for an ISP. Usually a local telephone number provides toll-free dialup access to an ISP. This service may also be an 800-number or other type of modem access.

POWER SUM - Testing CAT5, CAT6 cable. The current, best method of performance testing. Measures one twisted pair against the other three in the cable (P1-P2,P3,P4; P2-P1,P3,P4; etc.). If a cable manufacturer does not say they're doing Power Sum Testing, they probably aren't.

RETURN LOSS - Testing cable performance. Amount of energy robbed out of signal by impedance mismatches at connectors.

RSC - Refractive Synchronization Communication. Demonstrated data transfer rates of 200 gbps over 200 miles without signal amplification, using a single wavelength of light. The fastest fiber maxes out at 40 gbps. Uses to start summer, 1999.

SINGLE-MODE - Optical Fiber. A strand of fiber usually has: 8 micron diameter glass fiber core; 125 micron diameter cladding; a coating (brown or clear); and an outer buffer (one of 12 fiber color codes). Used in long-haul applications where cable is unlikely to be bent, such as cross-country cables (up to 125 Km). Light travels straight along the fiber core.

STP - Shielded Twisted Pair. This cable type is popular in Europe where there is greater concern about signal emissions.

UTP - Unshielded Twisted Pair. Two lengths of insulated copper wire, when twisted uniformly together (the number of twists per unit length remains fixed), will neutralize or throw-off extraneous interference signals. Cat5e cable, for example, uses four pairs of insulated copper wire with each pair using a different rate of twist. The relationship (spacing, air gap, rates of twist) of the conductors is maintained by outside jacketing of the cable.

UTP TESTING - Verifying performance of the entire cable. After cables and connector modules have been installed, tests for correct wiremap, attenuation, NEXT, and ACR must be done. Cable test devices do all of these tests for an installed length of cable almost simultaneously and in just a few seconds. Printed documentation verifies successful, passed tests.

VELOCITY OF PROPAGATION - Affects UTP performance. The speed of electrons in copper wire. Different rates of twist in a Cat5e cable result in different lengths of wire for each twisted pair. Negative effects of higher rates of twist call for larger wire diameter. The challenge in cable construction is to combine the best performance with the smallest wire size while producing an affordable product.

VIDEO BANDWIDTH - The maximum display resolution of a video screen, measured in millions of cycles per second (megahertz or MHz), and calculated by multiplying together horizontal pixels, vertical pixels, and refreshes per second. For example, 800 x 600 x 60 = 28.2 MHz. TV studio recording is limited to 5 MHz; TV broadcasting is limited to 3.58 MHz.