Operation Manual

Glossary
128
CROSSOVER—Wiring used when connecting a 10Base-T MAU to another 10Base-T
MAU or a 10Base-T hub to another 10Base-T hub. For example, one 10Base-T MAU has
the TD pair on the same pins as another 10Base-T MAU. If pins were wired straight,
there would be two transmitters on one pair and no receiver. As a solution, the crossover
cable crosses the TD pair with the RD pair, to connect the TD pins on one end to the RD
pins at the other end.
CYCLIC REDUNDANCY CODE (CRC)—An algorithm used to check for and correct
bit errors in data transmission.
DATA COMMUNICATION EQUIPMENT (DCE)—In RS232 specification a module,
such as a modem, for connecting a DTE to other equipment. A repeater connected to a
terminal or workstation for OMEGA management use is wired as a DCE.
DATA TERMINAL EQUIPMENT (DTE)—In RS232 specification a module typically
at the end of a segment. The DTE could be an Ethernet workstation, repeater or bridge.
EMULATED LOCAL AREA NETWORK (ELAN)—See LAN Emulation.
FOIRL — A fiber optic standard that allows up to 1,000 meters (3,280 ft.) of multimode
duplex fiber optic cable in a point-to-point link.
HOT SWAPPING— The process of replacing a module without interrupting the
network. This process occurs by sliding an active module into a fully powered up unit,
replacing a failed module.
HOUSE WIRING—House wiring is the existing wiring inside a building. This wiring
generally originates from one or more wiring closets, such as a telephone room. Some
older buildings may have wiring unsuitable for 10 megabit data rates. In these
circumstances, it is recommended that the wiring be tested with a 10Base-T signal/wire
tester.
HUB/REPEATER—A hub is a central signal distributor. It is used in a wiring topology
consisting of several point-to-point segments originating from a central point. The term
hub is often used interchangeably with the term repeater. Multiport 10Base-T, 10Base2
and fiber optic (10Base-FL, FOIRL) repeaters are considered hubs. See Repeater.
HUB-to-HUB WIRING—See MAU-to-MAU Wiring
HUB-to-MAU WIRING—UTP cables for 10Base-T hub-to-MAU or NIC cards are wired
straight-through. An RJ45 receptacle at the hub would wire pin-to-pin to the RJ45
receptacle at the MAU.
IMPEDANCE—An electrical characteristic of a circuit dealing with the combination of
the AC and DC resistance and the appearance of that resistance to attached circuits.
INTERIM LAYER MANAGEMENT INTERFACE (ILMI)—Protocol defined by the
ATM Forum UNI standards for managing the UNI.
JABBER LOCK-UP—The MAU’s ability to automatically inhibit the transmit data
from reaching the medium if the transmit data time exceeds a specified duration. This
duration is in the range of 20 ms to 150 ms. Jabber lock-up protects the medium from
being overrun with data packets from a possibly defective device.
JAM—This is a term used to describe the collision reinforcement signal output by the
repeater to all ports. The jam signal consists of 96 bits of alternating 1s and 0s. The
purpose is to extend a collision sufficiently so that all devices cease transmitting.
JITTER—The fluctuation of the data packet in respect to a standard clock cycle. Jitter
is undesirable and must be minimized.
LAN—See Local Area Network
LAN EMULATION—Methodology for mimicking the appearance of a LAN by
rendering the ATM switching fabric invisible to the user; enables user interface
software to treat a virtual LAN as if it were a physical LAN.