PPPD connection without interrupt

I try to get a system working with a modem and the following services :

1. permanent Data connection (2G/3G/4G) using old serial interface (not qmi/wmi)
2. permanent polling in AT command for getting SMS and get monitoring information like signal, provider, cell...

Does this modem can be connected 24/24 without any interruption ? Actually I have fast every day one or two small interruption of data (1 to 10 minutes).

The main question is, does a Modem can be connected to the provider 24/24 without interrupt, or it's a standard behavior to be disconnected sometimes ?

Additional note : I have multiples devices, and the PPPD binary fail in 10 minutes on all devices.

I have collect some logs, and I can see the system is disconnected each ~720 minutes = 12 hours :

Sep 14 20:23:02 daemon.info pppd[1905]: Connect time 718.6 minutes.
Sep 15 08:23:02 daemon.info pppd[19903]: Connect time 719.9 minutes.
Sep 15 20:23:03 daemon.info pppd[2493]: Connect time 719.9 minutes.
Sep 16 08:23:03 daemon.info pppd[16865]: Connect time 719.9 minutes.
Sep 16 20:23:03 daemon.info pppd[31234]: Connect time 719.8 minutes.
Sep 17 08:23:03 daemon.info pppd[13827]: Connect time 719.8 minutes.

Depending of the provider / cells. The system will de-register your modem each X hours (in my case 12 hours).

The best solution I have found is to set the option --persist on pppd. The system take ~1 minutes to re-register, but PPPD stay alive.