Hi Kalle,

> >> Huawei doesn't support CIND indications, so use CSQ instead. But
> >> naturally the response from modem is not according to standard:
> >
> > is this true for all Huawei modems?
> 

CSQ is not unsolicited, so you'd need to poll it.  Not a good idea.

> >> ofonod[6401]: < \r\n^BOOT:38645652,0,0,0,87\r\n
> >> ofonod[6401]: < \r\n^RSSI:23\r\n

I suggest you simply support this ^RSSI notification, it looks like it has the 
same 0-31 range as CSQ.  Also, sometimes values from vendor-specific commands 
differ from CSQ, so if a query of ^RSSI is supported, use that.

> Actually I didn't check that. I'll investigate more.
> 

ModemManager has done more work integrating ppp devices, poking around there 
can get you some hints.

Regards,
-Denis