Digi TransPort WR11 User Manual page 662

Configuring legacy protocols
When this optional feature is included, the device can be configured to pass X.25 calls or data received
in a TCP connection to another protocol or interface.
In addition, it is possible to specify a backup protocol or interface so if an outgoing call on one
interface fails, the backup interface is automatically tried. You can use LAPB to switch to either ISDN
or X.25 over serial, depending on the configuration of the LAPB instance chosen.
Digi TransPort® Routers User Guide
Configure Protocol Switch software
662