Glossary
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NETWORK SERVICES ACCESS POINT (NSAP)—OSI generic standard for a network
address consisting of 20 octets. ATM has specified E.164 for public network addressing and
the NSAP address structure for private network addresses.
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 RJ45 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.
PERMANENT VIRTUAL CIRCUIT (PVC)—A virtual circuit (x.25), virtual connection
(Frame Relay) or virtual channel connection (ATM) that has been established by manual or
semi-automated methods in advance of its need. Analogous to a leased/dedicated/
provisioned real circuit.
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.
RJ45—This connector is a 10BASE-T standard for connecting UTP cabling. It is
inexpensive and easy to install onto UTP cable.
SDH—See Synchronous Optical Network.
SIGNAL QUALITY ERROR (SQE) TEST—Signal indicates SQE function is active. The
SQE message is sent by the MAU to the DTE in the presence of a collision.
SIMPLE NETWORK MANAGEMENT PROTOCOL (SNMP)— SNMP is a TCP/IP
protocol that generally uses the User Datagram Protocol (UDP) to exchange messages
between a management information base and a management client residing on a network.
Since SNMP does not rely on the underlying communication protocols, it can be made
available over other protocols, such as XNS or DECnet.
SINGLE MODE FIBER—Type of fiber optic cable that uses wave propagation within a
homogenous medium to transmit signal over long-range distances (5 to 10 km). Requires
high-intensity laser light source (Class 1 emission).
SONET—See Synchronous Optical Network.
