Technical data

www.westermo.com Theoretical and general applications 155
Phase Modulation Affects the signals position during the period, phase angle, to
encode data bits. Phase modulation is primarily used in digital
transmisions.
Pin Terminal in e.g. a D-sub connector and on circuits intended for
mounting/ soldering.
PLC Programmable Logic Controller.
Polling Connected units are asked, polled, by the main computer
whether they have information to send.
POTS Plain Old Telephone System, same as PSTN
PPP Point to Point Protocol. A communication protocol enabling a
PC to connect and communicate to an additional Ethernet
connection via a serial link.
PRI Primary Rate Interface, ISDN-service that provides access to one
64 kbit/s D-channel and 30 B-channels (In Europe).
Priority Tagging The ability of an Ethernet network device to set a flag within an
Ethernet packet that enables it to have higher priority than other
packets on the same network.
PROFIBUS Standard for industrial data network.
Protocol Establishes regulations for data communications, how the signals
are interrelated, how they are sent, received, started and stopped
and how queues are handled, etc.
PSTN Public Switched Telephone Network, the common analogue tele-
phone system.
PTT-modem A modem for data communication via the Public Telephone
Network.
QoS Quality of Service. A definable service and quality level on net-
work services, for example, echo, noise, bit error frequency, con-
nection times, etc.
Rack modem For mounting in a 19" rack.
Remote Possibility, via some communication media (GSM, ISDN, line)
Connection to connect to off-site equipment.
Repeater Signal amplifier that recreates signals and allows
new segments to be added to the network.
Resistance The electrical resistance of the cable per kilometre.
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