Westermo TD-22 - Manual (Page 47)

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V.42bis.
Data Compression technique used by modems rather than MNP5, because it offers better
compression on already compressed data.
Data Rate
In modems this is often different to the baud rate. For instance the Data Rate of V.32bis is 14,400bps
and the baud is 2400 symbols/second.
Direct Mode
The Data to be transmitted is sent directly to the data pump. No compression, error correction or
buffering occurs, allowing the data to be transmitted across the link unaltered by the modem.
Duplex
Means that the communication is bi-directional. In half duplex, the devices take turns sending and
receiving. In full duplex, sending and receiving can take place simultaneously.
Handshaking
Confirmations and status signals sent between communicating devices in order to check the data
stream. There are two general types, hardware (RTS/CTS) and software (XON/XOFF). In hardware
handshaking the RS232 status lines are used to control data flow, whereas with the software method
characters are transmitted to control the data.
Hayes commands
A set of commands for controlling PTT modems. Often refereed to as the AT command set. Most
modems support these commands however there are many variations and some modems will support
commands that others can not.
LED
Light-Emitting Diode. A semi-conductor which emits light when it receives an electrical current.
Used as indicators.
Lease Line
A private point to point connection provided by a national or local telecommunication company.
These can be 2 or 4 wire point to point or even in a multidrop configuration.
Modem
Acronym of the words modulator and demodulator. Modulates or transforms the signal from
computer equipment into electrical signals for transmission. The receiver has a similar modem which
retransforms the signal, demodulation.
Modem Modulation Standards
V.21
300bps, similar to Bell 103
V.23 1200/75 bps Split speed line
V.23hdx 1200 multidrop lease line standard
V.22 1200 bps full duplex
V.22bis 2400 bps full duplex
V.32 9600 bps full duplex
V.32bis 14,400 bps full duplex