Comtech EF Data Vipersat Circuit Scheduler v3.7.x ArrangeLink - Manual (Page 83)

Appendix A - Glossary A-7
O
ODU Outdoor Unit – In a VSAT system, the RF components (transceiver) are usually
installed outdoors on the antenna structure itself and are thus referred to as an
ODU. The ODU typically includes the BUC and LNB, and is connected to the
IDU/modem by the IFL cabling.
P
PLDM Path Loss Data Message – A packet message that is sent by older Vipersat
modems (e.g., CDM-570/L) to the VMS every sixty seconds, providing status
update and operating parameter information.
PSK Phase-Shift Keying – A digital modulation scheme that conveys data by chang-
ing the phase of a base reference signal, the carrier wave. Different PSKs are
used, depending on the data rate required. Examples are binary phase-shift
keying (BPSK or 2-PSK) which uses two phases, and quadrature phase-shift
keying (QPSK) which uses four phases.
PSTN Public Switched Telephone Network – The world’s public circuit-switched
telephone network, digital and analog, and includes mobile as well as land-line
voice and data communications.
Q
QAM Quadrature Amplitude Modulation – A digital modulation technique in which
the amplitude of two carrier waves is changed to represent the data signal. These
two waves are 90 degrees out of phase with each other.
QoS Quality of Service
QPSK Quadrature Phase-Shift Keying – A digital modulation technique in which the
carrier is phase shifted +/- 90 or +/-180 degrees. With four phases, QPSK can
encode two bits per symbol—twice the rate of BPSK. However, it also uses
twice the power. Also known as 4-PSK or 4-QAM.