Westermo TD-22 - Manual (Page 48)

49 6177-2203
Modulation Techniques
DPSK
Differential Phase Shift Keying. employed in data rates up to 4800bps.
FSK
Frequency Shift Keying. Used in the lowest data rate standards.
QAM
Quadrature Amplitude Modulation. A technique used for data rates up to 9600.
TCM
Trellis Coded Modulation. Used in the highest speed modulations.
NVRAM
Non Volatile Random Access Memory. Used by the modem to store profile information and numbers
even when the unit has no power.
Normal Mode
A non error corrected connection between two modems. The data is however speed buffered.
Off Hook
Term used to describe when the modem is not connected to a telephone line.
On Hook
Term used to describe when the modem is using the telephone line.
PSTN
Public Switched Telephone Network.
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.
REN Number
The REN number of the TD-22 is 1
The Ringer Equivalence Number (REN) is a measure of apparatus performance when used with other
equipment connected to the same telephone line. The sum of the individual REN’s connected to a
single line should not exceed 4.