Snom ONE IP Technical Manual page 215

snom ONE • Administrator Guide, Release 5
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NTP (Network Time Protocol) [RFC 958]
A protocol for synchronizing the clocks of computer systems using a set of dis-
tributed clients and servers. NTP uses UDP on port 123 as its transport layer and
uses a jitter buffer to resist the effects of variable latency.
PBx (Private Branch exchange)
A telephone exchange that serves a particular business or office, as opposed to one
that is owned by a common carrier or telephone company and is used by many
businesses or the general public. Users of the PBX share a certain number of out-
side lines for making telephone calls external to the PBX. PBXs have evolved over
time, beginning as a manual switchboard or attendant console that was operated
by a telephone operator (circuit switching) to the modern IP PBX. See also "IP
PBX."
PCM (pulse code modulation)
A sampling technique that converts analog signals to digital form. The analog sig-
nal is represented by a series of pulses and non-pulses (1 or 0, respectively), and
the PCM performs the analog-to-digital conversion of the speech waveform by
sampling the signal 8000 times a second, encoding and transmitting the samples
in a serial bit stream as 8-bit digital words. Two standards are used for coding
the sample level: the U-Law standard (North America and Japan) and the A-Law
standard (used in most other countries). PCM makes it possible to digitize all
forms of analog data, including full-motion video, voices, music, telemetry, and
virtual reality.
POTS (Plain Old Telephone Service)
The standard telephone service that most homes use. The POTS network is also
called the PSTN. POTS is generally restricted to about 52 Kbps (52,000 bits per
second). Non-POTS telephone services, such as ISDN and FDDI, have high-
speed, digital communications lines.
Power over Ethernet (PoE)
A technology that allows the LAN switching infrastructure to provide power over
a copper Ethernet cable to an endpoint or powered device. With PoE, the electri-
cal current is not carried by power cords.