Westermo TD-32 - Manual (Page 52)

52 6178-2203
Modem
Acronym of the words modulator and demodulator. Modulates or transforms the signal from
computer equipment into electrical or acoustic signals for transmission. The receiver has a
similar modem which retransforms the signal, demodulation.
Modem Modulation Standards
V.21
300 bit/s, similar to Bell 103
V.23 1 200/75 bps Split speed line
V.23hdx 1 200 bit/s multidrop lease line standard
V.22 1 200 bit/s full duplex.
V.22bis 2 400 bit/s full duplex.
V.32 9 600 bit/s full duplex.
V.32bis 14 400 bit/s full duplex.
V.34 28 800 bit/s full duplex.
Modulation Techniques
DPSK
Differential Phase Shift Keying. Employed in data rates up to 4 800bps.
FSK
Frequency Shift Keying. Used in the lowest data rate standards.
QAM
Quadrature Amplitude Modulation. A technique used for data rates up to 9600 bps.
TCM
Trellis Coded Modulation. Used in the highest speed modulations.
NVRAM
Non Volatile Random Access Memory. Consists most often by an EEPROM (Electronically Eraseable
and Programmable 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, where data is buffered.
Off Hook
Like picking up the receiver. Connecting to a line.
On Hook
Like hanging up the receiver. Disconnecting.
PSTN
Public Switched Telephone Network, i.e. a normal telephone line on which other subscribers can be
called.
Parity
A mathematically derived bit which is added by the transmitter. The receiver checks it to detect any
error in transmission. Occurring parities are even, odd and none.
REN Number
The REN number of the TD-32 is 1.
The Ringer Equivalence Number (REN) is a way of measuring the load on the telephone line
caused by the connected equipment. REN equalling 1 corresponds to a normal phone. The Swedish
telephone lines can handle a load on 6 REN, which means that a maximum amount of 6 telephone
loads can be connected to the same phone connection simultaneously, without any problems.