Technical data

154 Theoretical and general applications www.westermo.com
Network General designation of communication links between two or
more pieces of equipment.
OPC Open Process Control. (Formally OLE Process Control).
An open standard that enables devices to openly communicate
with each other regardless of manufacturer.
Optocoupler Signal transmission via light, for example, light emitting diodes and
photo-transistors.
An optocoupler does not conduct electrical current and in thus
provides galvanic isolation.
Optoplexor Multiplexer for fibre cable. See multiplexer.
OSI Open System Interconnection, a reference model for the
definition of how data is handled in different communication lay-
ers when transferring.
Packet This is the unit of data that is passed between a source and desti-
nation device on the Internet. When data is requested from a
device the TCP layer of TCP/IP divides the file into chunks. Using
TCP/IP each of these packets is numbered and although routed
via different paths enables the packets to be correctly re-assem-
bled at the destination device. Packet sizes range from 48 Bytes
to 1518 Bytes (1522 Bytes if Priority Tagging is implemented).
PAP The Password Authentication Procedure. A password is sent as
clear text to the server for comparison.
Parallel transfer Simultaneous transfer of data bits on each line.
An 8-bit character (=1 byte) requires 8 parallel lines. 32-bit com-
munication transfers 4 bytes simultaneously on 32 parallel lines.
Parallel transfer primarily takes place internally in data equipment
and over very short distances.
Parity bit Mathematically calculated control bit that the transmitting equip-
ment adds. The receiving unit controls the parity and any errors
in the transfer are detected.
PDP Context Packet Data Protocol. PDP Context is information that defines a
GPRS connection between an MS (Mobile Station) and a GPRS
network. Context defines aspects such as routing, QoS
(Quality of Service.), security, tariffs, etc.
PDS Premises Distributed System. Refers to different levels of integrat-
ed systems for data communication, telecommunication, heating,
ventilation, monitoring, etc.
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