Random Modem Disconnect with WE826 and MC7455

[robl2e]

Hi,
With my current setup I noticed that the router would randomly disconnect the modem after being connected fine for several hours. The good thing is that the router is able to automatically reconnect the modem after a few minutes, but wondering if this is normal operation and if not what can I do to prevent this?

My setup is:

• WE826 Router with GoldenOrb_2018-11-03 ( OpenWrt 18.06.1 )

• MC7455 modem with fw GENERIC 02.30.01.01

• Sprint Lte Service

I've looked at the Modem Connection Logs:

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Sun Dec 23 13:16:57 2018 : Attempting to Connect Modem #1 (Sierra_Wireless,_Incorporated EM7455)
Sun Dec 23 13:17:08 2018 : Modem #1 Connected ( Sierra Wireless, Incorporated MC7455)
Sun Dec 23 23:08:08 2018 : Disconnect (Removed) Modem #1
Sun Dec 23 23:08:39 2018 : Attempting to Connect Modem #1 (Sierra_Wireless,_Incorporated EM7455)
Sun Dec 23 23:08:47 2018 : Modem #1 Connected ( Sierra Wireless, Incorporated MC7455)
Mon Dec 24 08:14:08 2018 : Disconnect (Removed) Modem #1
Mon Dec 24 08:14:37 2018 : Attempting to Connect Modem #1 (Sierra_Wireless,_Incorporated EM7455)
Mon Dec 24 08:14:45 2018 : Modem #1 Connected ( Sierra Wireless, Incorporated MC7455)

and I see the modem getting disconnected at one point on 23:08:08 then reconnect and after several hours later get disconnected again at 08:14:08.

I looked at the corresponding system logs and see:

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Sun Dec 23 23:06:26 2018 user.notice wrtbwmon: Cleanup backup
Sun Dec 23 23:08:02 2018 kern.info kernel: [24055.490777] usb 1-1.2: USB disconnect, device number 3
Sun Dec 23 23:08:02 2018 kern.info kernel: [24055.496838] qcserial ttyUSB0: Qualcomm USB modem converter now disconnected from ttyUSB0
Sun Dec 23 23:08:02 2018 kern.info kernel: [24055.505335] qcserial 1-1.2:1.0: device disconnected
Sun Dec 23 23:08:02 2018 kern.info kernel: [24055.510897] qcserial ttyUSB1: Qualcomm USB modem converter now disconnected from ttyUSB1
Sun Dec 23 23:08:02 2018 kern.info kernel: [24055.519472] qcserial 1-1.2:1.2: device disconnected
Sun Dec 23 23:08:03 2018 kern.info kernel: [24055.561972] qcserial ttyUSB2: Qualcomm USB modem converter now disconnected from ttyUSB2
Sun Dec 23 23:08:03 2018 kern.info kernel: [24055.570352] qcserial 1-1.2:1.3: device disconnected
Sun Dec 23 23:08:03 2018 kern.info kernel: [24055.575718] cdc_mbim 1-1.2:1.12 wwan0: unregister 'cdc_mbim' usb-101c0000.ehci-1.2, CDC MBIM
Sun Dec 23 23:08:03 2018 daemon.notice netifd: Network device 'wwan0' link is down
...
Mon Dec 24 08:14:00 2018 kern.info kernel: [47202.331813] usb 1-1.2: USB disconnect, device number 4
Mon Dec 24 08:14:00 2018 kern.info kernel: [47202.337543] qcserial ttyUSB0: Qualcomm USB modem converter now disconnected from ttyUSB0
Mon Dec 24 08:14:00 2018 kern.info kernel: [47202.346029] qcserial 1-1.2:1.0: device disconnected
Mon Dec 24 08:14:00 2018 kern.info kernel: [47202.351666] qcserial ttyUSB1: Qualcomm USB modem converter now disconnected from ttyUSB1
Mon Dec 24 08:14:00 2018 kern.info kernel: [47202.360146] qcserial 1-1.2:1.2: device disconnected
Mon Dec 24 08:14:00 2018 kern.info kernel: [47202.439181] qcserial ttyUSB2: Qualcomm USB modem converter now disconnected from ttyUSB2
Mon Dec 24 08:14:00 2018 kern.info kernel: [47202.447703] qcserial 1-1.2:1.3: device disconnected
Mon Dec 24 08:14:00 2018 kern.info kernel: [47202.453085] cdc_mbim 1-1.2:1.12 wwan0: unregister 'cdc_mbim' usb-101c0000.ehci-1.2, CDC MBIM
Mon Dec 24 08:14:00 2018 kern.warn kernel: [47202.466540] failed to kill vid 0081/0 for device wwan0
Mon Dec 24 08:14:00 2018 daemon.notice netifd: Network device 'wwan0' link is down
Mon Dec 24 08:14:01 2018 kern.info kernel: [47202.753727] do_page_fault(): sending SIGSEGV to gcom for invalid write access to 0041c000
Mon Dec 24 08:14:01 2018 kern.info kernel: [47202.762119] epc = 004036e9 in comgt[400000+6000]
Mon Dec 24 08:14:01 2018 kern.info kernel: [47202.766849] ra  = 0040369d in comgt[400000+6000]

from what I can see at 23:08:02 "usb 1-1.2: USB disconnect, device number 3" the router seems to be disconnecting the modem for some reason.

I've tried with both enabling and disabling "Connection Monitoring Status", but that does not seem to make a difference. If I use the Franklin R850 Hotspot that came with the Sprint service, I don't have this issue and the connection stays (though not sure if that's a similar comparison)

Besides this random modem disconnecting randomly, the build is working fine and I get internet no problem.
So any ideas why this is happening?

[JimHelms]

I do not know if it will help or not, but you may try adding the Sprint OTA APN in profile 3.

From the MODEM > MISCELLANEOUS > AT COMMAND run the following commands:

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at!entercnd="A710"
at+cgdcont=1,"ipv4v6","r.ispsn"
at+cgdcont=3,"ipv4v6","otasn"
at!reset!

[robl2e]

Thanks for the response. I tried as you suggested and added the Sprint OTA APN, but the setting didn't change the behavior. I still got the disconnect several hours later.

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Tue Dec 25 10:07:17 2018 : Modem #1 Connected ( Sierra Wireless, Incorporated MC7455)
Tue Dec 25 19:33:09 2018 : Disconnect (Removed) Modem #1
Tue Dec 25 19:33:39 2018 : Attempting to Connect Modem #1 (Sierra_Wireless,_Incorporated EM7455)
Tue Dec 25 19:33:48 2018 : Modem #1 Connected ( Sierra Wireless, Incorporated MC7455)