MM 1.14.2: Question about bearer disconnect

[Aleksander Morgado]

Hey Giacinto,

> > > We're running 1.14.2 on a Cinterion (PLS62W) module.
> > >
> > > The modem is connected for a while and suddenly loses registration
> > > causing MM to start a forced disconnect of the bearer, but the attempt
> > > at disconnection fails.
> > >
> > > Oct 29 22:11:24.709516 ModemManager[530]: <info>  [1604009484.709151]
> > > [modem0] state changed (connected -> disconnecting) Oct 29
> > > 22:11:24.768445 ModemManager[530]: <debug> [1604009484.768058]
> > > [modem0/bearer0] sending PDP context deactivation in primary port...
> > > Oct 29 22:11:24.772352 ModemManager[530]: <debug>
> > [1604009484.771977]
> > > [modem0/ttyACM1/at] device open count is 2 (open) Oct 29
> > > 22:11:24.777015 ModemManager[530]: <debug> [1604009484.776642]
> > > [modem0/ttyACM1/at] --> 'AT+CGACT=0,1<CR>'
> > > Oct 29 22:11:24.966486 ModemManager[530]: <debug>
> > [1604009484.965979]
> > > [modem0/ttyACM1/at] <-- '<CR><LF>+CME ERROR: 202<CR><LF>'
> > > Oct 29 22:11:24.968238 ModemManager[530]: <debug>
> > [1604009484.967858]
> > > [modem0/ttyACM1/at] invalid mobile equipment error code: 202
> >
> >
> > Is 202 a generic error code, or Cinterion specific? Did you look that up?
>
> 202 means "incorrect parameter"
> According to the ATC notes to the AT+CGACT command:
> - If activation or deactivation of a context fails, then AT+CEER may provide further informations about the reason.
> - For EPS, if an attempt is made to disconnect the last PDN connection, then the MT responds with ERROR or, if extended error responses are enabled, a +CME ERROR.
>
> this second clause applies here: it is not possible to deactivate the PDN linked with the LTE attach, as this would detach from the network completely.
>

That's inline with what we've seen in other modules, e.g. the u-blox
TOBY modules. The solution used there was just to assume the
disconnection was successful even if a specific error was reported:
https://gitlab.freedesktop.org/mobile-broadband/ModemManager/-/blob/master/plugins/ublox/mm-broadband-bearer-ublox.c#L676
Unfortunately, there's no common solution for all modules as each
manufacturer seems to choose a different error type to report this
issue :) We could apply the same logic to the Cinterion plugin.

-- 
Aleksander
https://aleksander.es