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Re: [lwip-users] Help with PPP connection - modem disconnects for no obv

From: Freddie Chopin
Subject: Re: [lwip-users] Help with PPP connection - modem disconnects for no obvious reason...
Date: Wed, 20 Mar 2019 19:29:31 +0100
User-agent: Evolution 3.30.5

Hello again Sylvain!

On Wed, 2019-03-20 at 18:22 +0100, Sylvain Rochet wrote:
> The DiscReq LCP packet does not seem to be related at all to the PPP 
> exchange, but rather just timed after the PPP session is started no 
> matter what, right ? Could you try aggressively slowing down the
> serial 
> tx routine to check that ?

This modem is connected with USB, so I could try adding a `sleep()`
inside the functions that read/write to the device. Would that be what
you have in mind? Previously I've tried to make sure this is not a case
of "modem disconnects X seconds after `ATD*99#`" so I've added a long
sleep (up to 60 seconds) between last AT command and starting lwip, but
this also did not change anything.

> Could you try using `AT+CGDATA="PPP",1` instead of `ATD*99#` ?

I'll try that - `ATD*99#` was recommended in the documentation for this
modem, so I used that.

> Your setup allows you to check using pppd instead of lwIP, maybe
> that's 
> worth trying it to get another set of traces.

Generally I think that using pppd is possible here, but the funny thing
is that the first thing I tried was to use this modem as a network card
with Linux - using NetworkManager, ModemManader, pppd and so on. And it
_DID_ connect to the network, got an IP address, DNS servers, etc.,
but... did not work at all (;


That's why I then tried in Windows and in there - after a couple of
tricks and hacks - it worked correctly. My plan was therefore to try
using Wireshark to capture USB traffic to this modem to see what's
going on, maybe this will me some hints (assuming I'll manage to do
that)... I'll try to use pppd with your suggestions too.

But generally - is it possible for the modem to misbehave like this
because of some lwip settings or maybe whatever I would set in lwip it
should not result in the modem just disconnecting? I'm not 100% sure
about any part of this code really, so don't know where to focus.


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