Setting the operating mode for physical interfaces
For a synchronous/asynchronous serial interface, set its operating mode depending on the connected modem. If the connected modem is asynchronous, set the interface to operate in asynchronous mode and then enable modem dial on the corresponding user interface. If the connected modem is synchronous, set the interface to operate in synchronous mode.
By default, a synchronous/asynchronous serial interface operates in synchronous mode, and an asynchronous serial interface operates in asynchronous mode.
For more information, see HPE FlexNetwork MSR Router Series Comware 5 Interface Configuration Guide and "Managing a modem."