NM frequently disconnects mobile broadband and refuses to reconnect -- Huawei E156G, E620

The problem seems to be that the modem times out responding:
<debug> [1300375162.083126] [mm-at-serial-port.c:298] debug_log(): (ttyACM1): <-- '<CR><LF>+CIND: 1,3,1,0,1,0,1,0,0,0,0,0<CR><LF><CR><LF>OK<CR><LF>'
<debug> [1300375191.980676] [mm-at-serial-port.c:298] debug_log(): (ttyACM1): --> 'AT+CIND?<CR>'
<debug> [1300375192.045069] [mm-at-serial-port.c:298] debug_log(): (ttyACM1): <-- 'AT+CIND'
<debug> [1300375192.076325] [mm-at-serial-port.c:298] debug_log(): (ttyACM1): <-- '?<CR>'
<debug> [1300375221.980631] [mm-at-serial-port.c:298] debug_log(): (ttyACM1): --> 'AT+CIND?<CR>'
<debug> [1300375251.980717] [mm-at-serial-port.c:298] debug_log(): (ttyACM1): --> 'AT+CIND?<CR>'
<debug> [1300375281.980735] [mm-at-serial-port.c:298] debug_log(): (ttyACM1): --> 'AT+CIND?<CR>'
<debug> [1300375304.750596] [mm-serial-port.c:798] mm_serial_port_close(): (ttyACM0) device open count is 0 (close)
<info> [1300375304.805987] [mm-serial-port.c:811] mm_serial_port_close(): (ttyACM0) closing serial port...
<debug> [1300375304.839035] [mm-port.c:181] mm_port_set_connected(): (ttyACM0): port now disconnected
<info> [1300375304.872109] [mm-serial-port.c:834] mm_serial_port_close(): (ttyACM0) serial port closed
<debug> [1300375304.905221] [mm-at-serial-port.c:298] debug_log(): (ttyACM1): <-- '<CR><LF>+CIND: 1,3,1,0,1,0,1,0,0,0,0,0<CR><LF><CR><LF>OK<CR><LF><CR><LF>+CIEV: 2,2<CR><LF><CR><LF>+CIEV: 2,3<CR><LF>'
<info> [1300375304.939062] [mm-modem.c:761] mm_modem_set_state(): Modem /org/freedesktop/ModemManager/Modems/0: state changed (connected -> disconnecting)
<info> [1300375304.971659] [mm-modem.c:761] mm_modem_set_state(): Modem /org/freedesktop/ModemManager/Modems/0: state changed (disconnecting -> connected)
<debug> [1300375306.610641] [mm-at-serial-port.c:298] debug_log(): (ttyACM1): <-- '<CR><LF>+CGREG: 1,"0CEC","01345890",4<CR><LF><CR><LF>+CREG: 1,"0CEC","01345890"<CR><LF>'
<debug> [1300375307.460661] [mm-at-serial-port.c:298] debug_log(): (ttyACM1): <-- '<CR><LF>+CIEV: 2,4<CR><LF>'
<debug> [1300375307.964547] [mm-generic-gsm.c:4361] simple_connect(): (ttyACM0): number => "*99#"
<debug> [1300375307.998269] [mm-generic-gsm.c:4361] simple_connect(): (ttyACM0): network_mode => 0
<debug> [1300375308.080864] [mm-generic-gsm.c:4361] simple_connect(): (ttyACM0): apn => "bsnlnet"
<debug> [1300375308.295288] [mm-generic-gsm.c:4361] simple_connect(): (ttyACM0): allowed_mode => 0
<debug> [1300375308.328472] [mm-generic-gsm.c:4250] simple_state_machine(): (ttyACM0): simple connect state 0
<debug> [1300375308.361563] [mm-generic-gsm.c:4250] simple_state_machine(): (ttyACM0): simple connect state 2
<info> [1300375308.396454] [mm-modem.c:761] mm_modem_set_state(): Modem /org/freedesktop/ModemManager/Modems/0: state changed (connected -> disconnecting)
<info> [1300375308.427854] [mm-modem.c:761] mm_modem_set_state(): Modem /org/freedesktop/ModemManager/Modems/0: state changed (disconnecting -> connected)
<debug> [1300375312.032212] [mm-generic-gsm.c:4361] simple_connect(): (ttyACM0): number => "*99#"
<debug> [1300375312.089508] [mm-generic-gsm.c:4361] simple_connect(): (ttyACM0): network_mode => 0
<debug> [1300375312.122620] [mm-generic-gsm.c:4361] simple_connect(): (ttyACM...

I'm able to reconnect manually immediately after it disconnects (to do this I need to disable 'mobile broadband' from nm-applet and enable it again.). as for the signal, its mostly good when this happens.

On maverick it used to reconnect automatically after a disconnect.

Yes. Exactly the same at Maverik. Huawei E156G.
(restart network-manager also doesn't help)

I'm not sure if its the same bug, but my 3G modem won't stay connected for more than a few seconds. It worked fine in 9.10, and continues to work fine in Windows, so I know its not a hardware issue.

Log attached.

I should add that I'm running 11.04 64 bit, with network manager 0.8.4~git.20110319t175609.d14809b-0ubuntu3, kernel 2.6.38-8-generic

Debug output from network-manager and modemmanager, as suggested here: http://ubuntuforums.org/showthread.php?t=1771723

I found a solution, for my problem at least. It turns out the problem was USB autosuspend.

as root:
echo on > /sys/bus/usb/devices/2-1.6/power/level

Now it stays connected.

Certainly, everyone's usb device path will differ.

Hope this helps.

I also face the same problem & this is very irritating..
(@Vincent How to find my usb devices path? )

Bus 001 Device 002: ID 12d1:1001 Huawei Technologies Co., Ltd. E620 USB Modem
  idVendor 0x12d1 Huawei Technologies Co., Ltd.
  idProduct 0x1001 E620 USB Modem

There is no direct way to find the USB device path that I know of. I followed this guide:
http://www.lesswatts.org/projects/devices-power-management/usb.php
You compare the bus# and device# from lsusb to "devnum" and "busnum" files in /sys/bus/usb/devices/*

This is probably the same bug as
https://bugs.launchpad.net/ubuntu/+source/network-manager/+bug/746078
and as
https://bugs.launchpad.net/ubuntu/+source/network-manager/+bug/435057

See also:
https://bugs.launchpad.net/ubuntu/+source/network-manager/+bug/438150

To everyone who has this problem: What modem (full name, please) do you have?

Ah, sorry, but I can't tell. It was a USB driven Huawei.

You know, this was a year ago. And the problem was with the internet connection. So repairing it was needed like water in the desert.

I tried hard for about a month or two, but ultimately failed with solving it with that modem. So I switched to another connection method (DSL) at another internet provider, gave my 3G modem to a guy who used another OS, and forget about the whole problem at all.

Probably I'll try to avoid anything from Huawei in the future. They should have a few developer working on native Ubuntu support for their products, don't they? But they seem to ignore Ubuntu, so I'll seem to ignore them at all.

The Huawei modem models that have been mentioned so far are not listed as supported upstream.

    https://live.gnome.org/NetworkManager/MobileBroadband/

If you would like your model to be supported by NetworkManager and modem-manager, please file a request in the upstream bug tracking system

    https://bugzilla.gnome.org/browse.cgi?product=NetworkManager

To save work, we don't track such requests in Launchpad as well --- marking Invalid.

"Known to work" is something completely different than "supported".