Hi Mylene,

 >
> ok thank you for the explanation.
> How atoms force to go back into AT commands mode ? Where is it done in the code ?
>

Each atom behaves differently.  Refer to the atom's remove() function 
for details.  E.g. the 'atmodem' gprs_context atom uses g_at_ppp_unref() 
and g_at_chat_resume() to force the chat out of PPP mode.  This is why 
you see "garbage" on the AT trace.  In reality it is just a final HDLC 
frame.

Regards,
-Denis