Allied Telesis AT-MR420TR Installation Manual page 61

AT-MR420TR and AT-MR820TR Installation Guide
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—STP/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.
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 shift of the data bit 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 that has no
MAU devices, but links together two LAN devices such as repeaters.
LINK TEST—In 10Base-T Ethernet there is a link test function that validates
the STP/UTP link. This consists of a pulse transmitted from point A on one pair
that is 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).
MAU—See Medium Attachment Unit
MAU-to-MAU, HUB-to-HUB WIRING—10Base-T MAU-to-MAU or hub-to-
hub wiring generally requires a cross-over cable located somewhere along the
STP/UTP cable run. This may commonly occur at the punch-down block or
between the RJ45 wall receptacle and the workstation.
MAU/TRANSCEIVER—An Ethernet transceiver is a MAU. A 10Base-T MAU
interfaces the STP/UTP media to an AUI port on a workstation, repeater,
bridge or other Ethernet device.
MDI/MDI-X—See Medium Dependent Interface
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