Westermo ID-90 - Manual (Page 117)

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On Hook
Term used to describe when the modem is using the telephone line.
OSI
Open System Interconnection.
Parity
A mathematically-derived bit which is added by the transmitter. The receiver checks the
sum of the parity bit to detect any error in transmission.
PBX
Private Branch Exchange.
PPP
Point-to-point protocol.
The Point-to-Point Protocol (PPP) provides a standard method for transporting multi-pro-
tocol datagrams over point-to-point links. using a HDLC-like framing for PPP encapsulat-
ed packets.
PRI/PRA
Primary Rate Interface / Primary Rate Access; the interface configuration with thirty 64
kbit/s information channels and one 64 kbit/s signalling channel.
Primary Acces
30B +1D.
Pseudo ternary code
Coding is performed in such a way that a binary ONE is represented by no line signal,
whereas a binary ZERO is represented by a positive or negative pulse. The first binary
ZERO following the frame bit-balance bit is of the same polarity as the framing bit-bal-
ance bit. Subsequent binary ZEROs must alternate in polarity.
A balance bit is a binary ZERO if the number of binary ZEROs following the previous
balance bit is odd. A balance bit is a binary ONE if the number of binary ZEROs follow-
ing the previous balance bit is even.
PSTN
Public Switched Telephone Network.
QAM
Quadrature Amplitude Modulation. A technique used for data rates up to 9 600.
Rate Adaptation
Also Rate Adaption. The process of converting a user's actual bit rate, which may be
56 Kb/s synchronous or 9.6 Kb/s asynchronous, to the 64 Kb/s speed of the B-channel.