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DEPARTMENT CONCENTRATOR
—Hub which provides a large
number of workstation connections. In this manual the term department
concentrator refers to multiple repeaters housed in an AT-36C8 chassis.
See Hub/Repeater, Repeater.
DIX CONNECTOR
—See D-Sub Connector
HARMONICA ADAPTER
—This adapter provides a simple way to convert
the 50-pin Telco connection to RJ45 connections.
HEARTBEAT
—See SQE
HUB to HUB WIRING
—See Hub to MAU Wiring
HUB to MAU WIRING
—UTP cables for 10BASE-T hub-to-MAU or
Network Interface Controller (NIC) cards are wired straight-through. An
RJ45 receptacle at the hub would wire pin to pin to the RJ45 receptacle at the
MAU.
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.
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 is tested with a 10BASE-T signal/wire tester.
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.
JABBER LOCK-UP
—The MAU’s ability to automatically inhibit the
transmit data from reaching the medium if the transmit data time length
exceeds 150 ms duration. This 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 MAU onto the transmission medium if the transmit data time
length exceeds 150
µ
s duration. This protects the medium from being overrun
with data packets from a possibly defective device.
JITTER
—The fluctuation of the data packet in respect to a standard clock
cycle. Jitter is undesirable and must be minimized.
LINK SEGMENT
—The link segment of coaxial cable is a segment which
has no MAU devices but links two LAN devices together such as repeaters.
LINK TEST
—In 10BASE-T Ethernet there is a link test function that
validates the UTP link. This consists of a pulse transmitted from point A on
one pair and validated at point B. Point B also transmits a pulse on the second
pair to be validated by point A. These pulses occur during media idle states
(in between packets).
