Re: Differences between GSM modems

On 25 March 2017 at 06:31 Dan Williams <dcbw redhat com> wrote:

On Fri, 2017-03-24 at 13:53 +0000, Colin Helliwell wrote:

On 23 March 2017 at 19:43 Dan Williams <dcbw redhat com> wrote:

On Thu, 2017-03-23 at 18:26 +0000, colin helliwell ln-systems com

NetworkManager[1398]: [1490292215.0368] (ttyMux1): modem
changed, 'connected' --> 'registered' (reason: user-requested)
NetworkManager[1398]: [1490292215.0371] device (ttyMux1):
change: activated -> failed (reason 'modem-no-carrier') [100 120
NetworkManager[1398]: [1490292215.0390]
active-connection[0x1f38140]: set state deactivated (was
NetworkManager[1398]: [1490292215.0395]

We'll need ModemManager logs here; MM is saying the modem state
changed, possibly due to status changes on the secondary AT port.
hears that and terminates the connection.

Log including MM below.

But I think I've spotted the cause - the AT+CGACT? is getting a
'deactivated' response (@ 09:28:54). Hence MM seeing it as being

As Aleksander commented before (
s/modemmanager-devel/2017-March/004042.html), it doesn't make sense
to have different PDP's across multiple TTYs. And indeed their EHS5
appears to behave sensibly i.e. indicates the port 1 PDP as active
even if queried over [Primary] port 2.

However, on trawling through the BGS2 docs, I've found that that "PDP
contexts can be defined on any [mux] channel, but are visible and
usable only on the channel on which they are defined".
And doing some manual tests seems to confirm that - they can indeed
be set up independantly on different ports. Nice 'feature'.... :S
(I'm wondering if that's also behind some of the other weird sh^t
I've been grappling with).

That is... interesting. And unlike anything I've ever encountered
before :) If there's a way to detect that it's a BGS2, then we'll need
to special-case that device and stop ModemManager from polling
bearer/connection status. We might also need to somehow suppress the
MM disconnect behavior of sending CGACT=x,0 on the secondary port while
trying to ensure that PPP terminates and the data port returns to
command mode.

I wondered about altering the MM behaviour for it too - wasn't sure if it would be sane/possible to mess with 
with its 'view of the world' though. (Or, especially, worried about the likelihood of me doing it badly ;) ). 
Would it and/or NM lose some of its consequent abilities by no longer polling the connection status?
In part I'm tempted to drop the BGS2 as a 'bad job' and just use EHS5. Trouble is that many of our 
applications don't need the 3G capability of the latter, and there's quite a significant difference in BOM 
cost between the two.

I guess the "model" string would identify it?

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