Hey, > > First what are the conditions where a cellular data connection will be > automatically disconnected due to bad signal/loss of network? Also what > program handles the disconnect (NetworkManager, ModemManager, pppd)? >
It's the modem firmware itself handling that, MM will just report whatever the modem is reporting. E.g. if the modem is registered and connected in LTE, and the LTE network disappears (e.g. low signal quality, out of coverage) then the modem will try to handover to 3G or 2G transparently if there is any 3G or 2G around. While this is happening, the modem will definitely report that it's no longer registered in LTE (e.g. the CEREG:4 and CEREG:0 you see in the logs), it will also probably say that it's searching for some other non-LTE network via CREG/CGREG URCs, and while all that is happening, the modem will still keep saying that it's connected (the response to the periodic CGACT? states that the PDP context / EPS bearer is still connected). ModemManager will say that the modem is disconnected only when the CGACT? response reports that our specific CID isn't active. See below. So signal quality is 0: > May 6 18:31:25 canect2 daemon.debug ModemManager[304]: <debug> > [1557167485.896059] (ttyACM1): --> 'AT+CSQ<CR>' > May 6 18:31:25 canect2 daemon.debug ModemManager[304]: <debug> > [1557167485.899223] (ttyACM1): <-- '<CR><LF>+CSQ: > 99,99<CR><LF><CR><LF>OK<CR><LF>' > May 6 18:31:25 canect2 daemon.debug ModemManager[304]: <debug> > [1557167485.900293] Modem /org/freedesktop/ModemManager1/Modem/0: signal > quality updated (0) But still CGACT? reports that context with CID #2 is ACTIVE: > May 6 18:31:30 canect2 daemon.debug ModemManager[304]: <debug> > [1557167490.876303] (ttyACM1): --> 'AT+CGACT?<CR>' > May 6 18:31:30 canect2 daemon.debug ModemManager[304]: <debug> > [1557167490.882310] (ttyACM1): <-- '<CR><LF>+CGACT: > 1,0<CR><LF><CR><LF>+CGACT: 2,1<CR><LF><CR><LF>+CGACT: > 3,0<CR><LF><CR><LF>+CGACT: 4,0<CR><LF><CR><LF>+CGACT: > 5,0<CR><LF><CR><LF>+CGACT: 6,0<CR><LF><CR><LF>+C > May 6 18:31:30 canect2 daemon.debug ModemManager[304]: <debug> > [1557167490.883392] connection status loaded: connected Now, no LTE, but registering in CS > May 6 18:31:48 canect2 daemon.debug ModemManager[304]: <debug> > [1557167508.641702] (ttyACM1): <-- '<CR><LF>+CREG: > 1,"0000","0331E70C",7<CR><LF><CR><LF>+CGREG: 4<CR><LF><CR><LF>+CIEV: > 3,1<CR><LF><CR><LF>+CEREG: 0<CR><LF>' > May 6 18:31:48 canect2 daemon.info ModemManager[304]: <info> > [1557167508.642347] Modem /org/freedesktop/ModemManager1/Modem/0: 3GPP > Registration state changed (searching -> registering) Looks like pppd detects a disconnection itself here: > May 6 18:31:48 canect2 daemon.notice pppd[540]: Modem hangup Which is in line with the result of the next CGACT? check, where CID #2 is now reported as INACTIVE: > May 6 18:31:50 canect2 daemon.debug ModemManager[304]: <debug> > [1557167510.873812] (ttyACM1): --> 'AT+CGACT?<CR>' > May 6 18:31:50 canect2 daemon.debug ModemManager[304]: <debug> > [1557167510.880002] (ttyACM1): <-- '<CR><LF>+CGACT: > 1,0<CR><LF><CR><LF>+CGACT: 2,0<CR><LF><CR><LF>+CGACT: > 3,0<CR><LF><CR><LF>+CGACT: 4,0<CR><LF><CR><LF>+CGACT: > 5,0<CR><LF><CR><LF>+CGACT: 6,0<CR><LF><CR><LF>+C > May 6 18:31:50 canect2 daemon.debug ModemManager[304]: <debug> > [1557167510.881410] connection status loaded: disconnected > May 6 18:31:50 canect2 daemon.warn ModemManager[304]: <warn> > [1557167510.882008] (ttyACM0): could not re-acquire serial port lock: (5) > Input/output error > May 6 18:31:50 canect2 daemon.debug ModemManager[304]: <debug> > [1557167510.882435] (ttyACM0): port now disconnected And modem is reported disconnected in MM now. > May 6 18:31:50 canect2 daemon.info ModemManager[304]: <info> > [1557167510.882875] Modem /org/freedesktop/ModemManager1/Modem/0: state > changed (connected -> registered) There's a thing here, though. For this kind of modems where PPP is used, maybe we shouldn't be doing the periodic CGACT? checks through the secondary TTY. This is an open point I have in mind to review, because if we end up reporting the disconnection via MM (because CGACT reports no active CIDs) then the pppd shutdown process may not be happening properly in NM and the connected TTY may not go well back to command mode. I think there was some open issue about this. -- Aleksander https://aleksander.es _______________________________________________ ModemManager-devel mailing list ModemManager-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/modemmanager-devel
