Westermo TD-22 - Manual (Page 45)

Leased line applications
Leased line connections can be done using either 2-wire or 4-wire.
When renting a 4-wire line from a telephone company one pair of cables for transmission and one
pair for reception are usually provided.
The maximum transmission distance depends on the attenuation of the line. To have a good error rate
it is recommended to keep the attenuation under 20 dB, which is approximately 20 km in distance.
When renting lines from a telephone company a longer transmission distance is normally possible as
the signals are probably transmitted over PCM-lines, i.e. fibre optic or other media with low
attenuation.
The best way to set the modem for leased line applications is to use the dip switches.
The settings should be as follows:
SW1:1 and 2 in modem no 1 ON and only SW1:2 in modem no 2 ON.
SW3:1 shall be ON for 2-wire and OFF for 4-wire.
SW3:3 shall be ON. Sets error correction and data compression OFF.
SW4 sets speed and parity for the RS-232 port.
SW5 decides line-speed. Must be set in direct mode applications.
46 6177-2203