Allied Telesis AT-MR815T - Manual (Page 42)

Glossary
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MANAGEMENT INFORMATION BASE (MIB)—A data base of network
configuration and performance information. The formal definition of a MIB
includes the names of the objects it contains and the type of information
retained. Management protocols such as SNMP and CMIP contain procedures
for acquiring and exchanging MIB information.
PATCH PANEL—A 10Base-T patch panel may be used between a punch-
down block and UTP workstation. The patch panel generally has a female
RJ-45 connector on the front for each workstation and a Telco (RJ21) connector
on the back, which is wired to a punch-down block. This provides a convenient
way for the installer or network manager to connect the hub 10Base-T ports
into the desired building locations.
PHYSICAL MEDIUM ATTACHMENT (PMA)—The portion of the MAU
that contains the functional circuitry.
PHYSICAL SIGNALING (PLS)—That portion of the physical layer
contained within the DTE that provides the logical and functional coupling
between MAU and data link layers.
POLARITY CORRECTION—Many 10Base-T UTP ports have a polarity
correction function. If the UTP wiring has RD- and RD+ inadvertently crossed,
the polarity correction function will sample the signal and electrically swap
the wires. If the TD- and TD+ wires are crossed, the correction would occur at
the MAU on the other end of the UTP link. This occurs within a single pair
and should not be confused with the crossover cable.
PROPAGATION DELAY—The time it takes a signal to travel from the input
of a system component to the output. Usually measured in nanoseconds. IEEE
802.3 has specific propagation delay maxima for computing propagation
budgets when designing a LAN. Cable length plays a major role in propagation
delay; for example, a 50-meter (164-foot) AUI cable has a maximum allowable
propagation delay of 257 ns. The propagation delay of cable depends on the
length and velocity factor of the cable type. There are also propagation delays
associated with electronics attached to the system.
PUNCH-DOWN BLOCK—The punch-down block is the wiring panel where
the house wiring from the building’s offices terminates. This is where many
10Base-T hubs would be located. Wiring installers use a special punch-down
tool to insert the UTP wire for data and voice applications.
REPEATER—A device used to extend the length, topology, or
interconnectivity of the physical medium beyond that imposed by a single
segment, up to the maximum allowable end-to-end trunk transmission line
length. Repeaters perform the basic actions of restoring signal amplitude,
waveform and timing applied to normal data and collision signals.
RJ-45—This connector is a 10Base-T standard for connecting UTP cabling. It
is inexpensive and easy to install onto UTP cable.