Appendix D. Glossary
D-8 MX2800 User Manual 61200290L1-1
NC
normally closed. Relay switch contacts that remain closed when inactive.
near end
The unit on-site.
NI
network interface. The demarcation point between the CPE and the PSTN.
NO
normally open. Relay switch contacts that remain open when inactive.
NRZ
non return to zero. A mode in which the digital level is low for a 0 bit and high
for a 1 bit, and does not return to zero between successive 1 bits.
out-of-band
Signaling that is separated from the channel carrying information (voice, data,
video, etc.). Typically the separation is accomplished by a filter. The signaling
includes dialing and other supervisory signals.
point-to-point
Type of communications link that connects a single device to another single
device, such as a remote terminal to a host computer.
POP
point of presence. Physical place within a LATA (local access and transport area)
where a long distance carrier or a cellular provider interfaces with the network
of the local exchange carrier (LEC). A POP is usually a building serving as the
point of termination which houses switches and transmission equipment.
protocol
A set of rules controlling the orderly exchange of information between stations
in data communications networks or systems.
PSTN
public switched telephone network. Usually refers to the world wide voice tele-
phone network available for public use.
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