@paul-thornton There it is. Thanks.
No one has replied
@robert-hh I thought so. Thanks.
Check lte.pppsuspend() and lte.pppresume() methods.
Ah ah ! I found my mistake :-) it works now when i initialize my serial port as follow :
stty -F /dev/ttyAMA0 921600 raw -echo -echoe -echok -crtscts