Modem Disconnecting

[ph34rful]

I've indeed been wondering if it might be the USB power cable. I tried several different ones and did not notice any change, but they were at least 36". Strangely when I tested the device at my home before transferring it to my relative's there were absolutely no issues, but the signal strength is much better at my location so that's why I think it may be related. I'll probably buy the USB cable here: https://ltefix.com/shop/cables/usb-cabl ... ower-cord/
Just to rule out it being the cable. Do you happen to know if it's possible to lock the device to band 30? It seemed the drops were much less frequent on that band and it had the best speed as well. I had limited time to troubleshoot the last time I was there, but it seemed like only B2, B4, B12, B66 were supported for band lock. When I tried the command I found for B30, it seemed like I couldn't get it take/lock, but it's possible I wasn't doing it correctly. I'll have another opportunity at Thanksgiving to work on it and would like to go back with the equipment and/or knowledge needed to make it more reliable. It's been so frustrating that I've seriously considered just buying the Mofi 4500 LTE. When the current setup doesn't drop the connection and ends up on band 30 the speeds are pretty decent at 10-15mbps, but it's just so inconsistent with the many connection drops, particularly when on other bands.

Edit: Connection monitoring has always been disabled on the Golden Orb device. Also, thanks for this site! Wish it had been available when I was putting the device together in December 2017. Definitely would have made things easier, I've spent god knows how many hours trying to figure this stuff out!

[Mchccjg12]

I've had similar issues with Sprint. My modem will disconnect pretty often, sometimes every 10 minutes, sometimes ever couple of hours. I have my MC7455 in an enclosure hooked up to a Raspberry Pi 2 B+ running Goldenorb.

EDIT: I have noticed something though, and it seems to be that most people with disconnect issues like I have seem to have a USB enclosure. I wonder if it is just a problem with the enclosure itself? Has anyone had issues with disconnects after they put the MC7455 into a router?

[JimHelms]

There is a new firmware for the MC7455 that is supposed to address some issues with Sprint. May be worth trying.

[Mchccjg12]

I'll try that shortly and report back, I didn't notice that a new generic firmware was released. Have you updated yours to the new firmware? I would like to make sure it works just in case there are issues, as I don't have a backup of the previous firmware version to revert to.

Thank you!

PS. I'll also be trying something else to fix the power issue to see if it is that, and I will report my results on that as well!

[JimHelms]

Yes, I have used the update with no issue.

Also of interest to Sprint users is one of Sierra's notes regarding the update:

Merge Qualcomm Stack MDM9635M.LE.3.0.c2-000010218.1 to address multiple issues, including:
– MOLEMMC9X30-1117: Module crashing on Sprint network in certain locations when CA is activated"

[Mchccjg12]

Thank you for responding! I'll be updating the firmware soon then. Also, after a peek through the release notes, I found something that I think would be a fix for it as well:

MC7455 resets periodically on Sprint network - Crash 3

Which is a fix related to RRC. Which, I had noticed, had issues on the debug for the modem. I noticed that when I turned off connection monitoring, I could look at the debug and see that the modem was still connected, with only one difference... RRC was in idle instead of connected.

Disconnected modem:

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Current Time:  481		Temperature: 32
Reset Counter: 1		Mode:        ONLINE         
System mode:   LTE        	PS state:    Attached     
LTE band:      B25    		LTE bw:      5 MHz   
LTE Rx chan:   8665		LTE Tx chan: 26665
LTE CA state:  NOT ASSIGNED
EMM state:     Registered     	Normal Service 
RRC state:     RRC Idle       
IMS reg state: No Srv  		
PCC RxM RSSI:  -74		RSRP (dBm):  -100
PCC RxD RSSI:  -69		RSRP (dBm):  -95
Tx Power:      0		TAC:         2115 (8469)
RSRQ (dB):     -10.4		Cell ID:     03E2D501 (65197313)
SINR (dB):     23.0
OK

Connected modem:

Code: Select all

Current Time:  58		Temperature: 32
Reset Counter: 2		Mode:        ONLINE         
System mode:   LTE        	PS state:    Attached     
LTE band:      B25    		LTE bw:      5 MHz   
LTE Rx chan:   8665		LTE Tx chan: 26665
LTE CA state:  NOT ASSIGNED
EMM state:     Registered     	Normal Service 
RRC state:     RRC Connected
IMS reg state: No Srv  		
PCC RxM RSSI:  -82		RSRP (dBm):  -102
PCC RxD RSSI:  -75		RSRP (dBm):  -94
Tx Power:      0		TAC:         2115 (8469)
RSRQ (dB):     -5.7		Cell ID:     03E2D501 (65197313)
SINR (dB):     24.8
OK

From what I've read on RRC, idle means no internet connection, and it is normally a power saving feature. So hopefully this firmware should prove pretty useful in finally solving these disconnect issues!

EDIT: Seems I am still having disconnects related to RRC going Idle, even after the firmware update.

[JimHelms]

Hmm... If the RRC is related to the low power mode, then try the following commands that are related to LPM:

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AT!ENTERCND="A710"
AT!CUSTOM="SIMLPM",2
AT!PCOFFEN=2
AT+CFUN=1
AT!RESET

[Mchccjg12]

Ok, seems that even after all of that, it is still disconnect, now every 5 seconds. Looking at the debug to try to figure things out, I noticed a few things.

Usually EMM state reads:
EMM state: Registered Normal Service

but before RRC does this and cuts the internet connection:
EMM state: SR Initiated ---

And then RRC reads:
RRC state: RRC Idle


So, I have no idea what is causing it, but it seems the RRC fix in the new firmware doesn't really help, even after a RMARESET.

EDIT: Apologies, seems I am dumb. I checked the version of the firmware after I did the RMARESET, and it seems that the command set the modem back to version 2.20.3, from the latest 2.30.1. So that's why it started to disconnect so much. I didn't think that the reset would revert to an older firmware version.

Though it seems even after setting the device back to the newest firmware, it still has issues... I wonder if Sprint's network just can't support it anymore.

EDIT 2: I'm at my wits end trying to solve this issue. I can't for the life of me figure out why it keeps disconnecting from the network. The ZTE Pocket Wifi works fine, so it's not an issue with the cell tower. It's something to do with the MC7455, and I can't seem to find a way to do anything about it. The weird thing is, it happens sporadically. Some days, it can be a bit better, and others, I can't go 5 minutes without it disconnecting over and over.

Also, just curious... is there any way to get the APN to stick? I read up that it might be IPV6 which is causing the issue, and using at+cgdcont to set the APN to use only IPv4 could help. However, it never seems to work, and always reverts to IPv4/v6.

Edit 3: I don't know if this matters or not, but this appeared in the system log when the modem seemed to not have an internet connection while connected to the network:
Fri Sep 28 01:17:18 2018 user.notice MBIM Monitor: Modem 1 Connection is Down (activation state: deactivated)
The way it looks, this doesn't have to do with connection monitoring.

[Mchccjg12]

So, I called Sprint tech support to try to solve the disconnect issue with the MC7455, and take this with a grain of salt, as it's possible that it is false. But, I was told that they have made recent changes to the network to further disallow devices like the MC7455 to work. Basically, it will boot it off, even with generic firmware. It is a recent change that is apparently still rolling out, so it does at least make a bit of sense; My setup worked for a while until it suddenly stopped working, and many others had a similar thing happen to them. This doesn't bode well for those that use the MC7455 on Sprint, especially since they refused to authorize/add my device to the account as well. Though, it seems the Mofi SIM4 might still work? But I can't say for sure.

[JimHelms]

Interesting what the Sprint tech said, but I would take it with a grain of salt.

Run this command and post the return:

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at!entercnd="A710"
at+cgdcont?

I have seen some strange OTA APN's automatically showing up as #3 and #13.

It is not uncommon for the RRC to be idle when no data is being pulled. It could however, be in the idle state as a result of something else going on.

While your modem is in the RRC state, run these commands and see what happens:

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at!entercnd="A710"
AT!SCACT=1,1