innovaphone gateway
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network in public communication technology.
P
PL
PL (
P
acket
L
oss) occurs during packet-based data transfer in networks.
Packet loss can occur in various layers of the OSI model.
PCM
PCM (
P
ulse
C
ode
M
odulation) is an ITU standard for the digitization of
voice, which is described in G.711. With this type of modulation, analogue
signals are converted to discrete-time and discrete-value binary signals
through quantisation.
In voice transmission, the PCM technique is used to convert an analogue
voice signal to a digital signal based on Nyquist’s sampling theorem. For this,
the analogue signal is sampled 8,000 times per second and is converted to
an 8-bit number, so that a sample value arises every 125 µs. The resulting
transfer speed is 64 kbit/s, the transferable voice frequency 4 kHz.
For the dynamisation of voice, the ITU within G.711 has defined two
methods for the dynamic compression: the µ-law method and the A-law
method.
PING
The ping program (
P
acket
I
nter
n
et
G
rouper) can be used to check whether
a particular host in an IP network is accessible and what its response time is.
POE
PoE (
P
ower
o
ver
E
thernet) describes a technology, with which network-
enabled devices can be supplied with power over the 8-wire Ethernet cable.
POSIX
POSIX (
P
ortable
O
perating
S
ystem
I
nterface for Uni
X
) is a standardised
application-level interface jointly developed by the IEEE (
I
nstitute of
E
lectrical and
E
lectronics
E
ngineers) and the Open Group for Unix. It
