Modem Hangs


before asking questions, i always search in the forum but searching tool is very bad and doesnt give me any result anyway.

i have a problem with fastrack supreme 20, OAT 663g00 v4.25.01 inside. My application works well for days but sometimes it get stucks, freezes and stop responding any command.

when i dial the number outside, it doesnt give me response that means sim is not active that time. this happens rare and modems are far away from us so we can not test why it hangs.

i want to know any idea about modem freezings. can there be any software or hardware problem that hangs the modems?

What doesn’t give you response, exactly?

Are you sure that your application fully checks all possible return values from all API calls?

Have you carefully considered all possible fault conditions - such as unexpected loss of service, unexpected dropped calls, safe handling of unexpected incoming calls, messages, etc…?

Yes, it does have problems.

If you log-in to your Developer page, there is a Feedback link there by which you can report your problems to Wavecom.

They do listen to comments via that link - see: viewtopic.php?f=8&t=2453&p=10149&hilit=search#p10149

i dial the number from my phone and it say “…can not be reached at the moment. pls try again later…” means that sim is not active

i handled the all return values written in the documantations. And when an event handled, i write that in flash as a log so i may check later. but there is no unexpectional events on the logs. When i make a hard reset to the modem, it usually starts running again.

i really couldnt find the reason. this is hard to test because it doesnt happen too often.

Not necessarily - it could just mean that the unit currently has no service.

If you call it from another Wavecom unit, you might get some additional hints from the +WIND: 5 & 6 events, and/or from AT+CEER…

Is it contactable by SMS?

Is it in an area of known poor signal?

Could somebody have turned it off - accidentally or otherwise?

Yes, those are always the worst bugs to find - especially when compounded by being remote!

You just need to try to add as much diagnostic capability as possible, and ensure that your application is as resilient as possible.

eg, if the unit hasn’t had a successful communication for some time, make it reset itself…

Are there people around at the site who you could talk to - see if they noticed anything unusual…

it is not contactable by SMS when it happens. there is no signal problem bc there are many modems comminicating at the same place. And nobody turns it off bc when it happens, modem’s led is always shining. when we make hard reset then it turns to normal behaviors.

i didnt want to do this but i may have to do that periodic reset bc of this issue. may be i will set a timer interval of 3 hours, and check wheater it is OO:OO AM so it should reset itself. but i am not even sure about that reset attemp will work when it hangs.

That isn’t necessarily true: antenna positioning can be quite critical - you might just have happened to put this one in a “dead” spot.

It could also be that the signal at this location is poor, but just acceptable for the other modems - and this one just happens to be a little less sensitive and/or is in a particular position where the signal is particularly bad…

Have you actually checked the signal?
Do your diagnostics record signal strength, and registration state?

Also, if there’s “many” modems, they could be interfering, or the netwrok could be congested…

You mean, when you get to it the LED is “shining” ?
But how do you know that someone didn’t turn it off earlier, and it failed to restart properly - leaving it in this state when you found it?
Or maybe there was a power glitch?

What do you mean by “shining”?
IF the LED is in the steady-ON state (constantly illuminated - not blinking), it means the unit is not registered to the GSM network.

In this state, does it still respond to local AT commands?

it is not blinking at that state. i couldnt try to send at commands yet when it happens. i am waiting it to happen again.

you are right , it could be bc of the signal quality and other modems can be in a better signaling area even if they are so close to eachothers. and should i change the antennas if the problem is bc of that. and one more info, i went that place and check the signal length by my phone, it shows 3/4 length(means good).

but what i dont understand is that modem comminicate and no problems then after some days it get stucks again. and hard reset solves it.

i will try to send at commands when it happens again.

That is almost entirely irrelevant.

Your phone is a different device, with a different antenna, at a different position - is it even on the same network?

You really need to see what signal strength your actual device is actually receiving itself; ie, what +CSQ value it has.
Maybe its antenna is badly positioned?
Maybe its antenna and/or the cable is faulty or damaged…

Again, if the signal strength is marginal, the device could easily work for some time, then it only takes some small change for the signal to go from “barely OK” to “no good”

Signal strength can vary widely - so, even if it is good when you’re there to take a measurement, it can fade in & out.
That’s why you need your application to log signal strength - so you can see if there’s any trends…

thank you for the tips. i will try to do a better testing . i may log csq values as you said.

thank you for the ideas, i will return back with my test results.

We have the same problem here , 1 of 20 modems hang a week since firmware version 663q… so we think it could be a firmware problem . the open at application stop working completely and no reset timer can bring live back. Just hard reset (power on off cyle) can help. beside this also io stop working status led going dark and so on…

We have Q2686 Firmware 663q …

any solutions right now or same observations ?

Reg, Robert

we have faced this problem with the firmware version 663g,663f. unfortunaletly we couldnt take any steps to the solution. if you solve the problem or get any idea for that, please share us. i will do the same


i dont know if you still follow this topic. i have experienced this problem again. And then i went there to see if i can connect modem by terminal or not. And i saw that i can connect by terminal although modem is still hanged and its led is not blinking always shining.

Also i read its logs and saw that its application still running on it. If i summerize it :

Modem is hanged and can not receive any sms or any calls.
Modem’s led is not blinlking , its led is always shining.
We can connect modem by terminal.
Modem’s application is still running and doing its other jobs.

So if modem application is still running then we could have caugth the reason or an error event when this hanging problem occured. But how? Any idea to what i should check when the modem is in hang mode. Or what can i control on the application to get know that modem is gonna be in hang mode. Or should i just reset the modem periodicly?

That certainly means that the modem has no GSM service - therefore, obviously, it cannot make or receive calls, nor send or receive texts.

What do you mean by “connect” here?

I presume you mean that you can plug-in a serial cable directly to the modem, send AT commands, and receive responses?
In that case you should try issuing commands like AT+CSQ and AT+COPS and AT+CREG to determine the state of GSM service.

Yes, of course it should be able to continue doing anything that doesn’t depend upon GSM service!

See above.

yes i mean i can send at commands and get responses. I send AT+CSQ and it returned normal value which is CSQ: 16,… I didnt send AT+COPS and AT+CREG. i should have sent those. anyway next time i will. So what i should do is to check AT+CREG values for example every 3 hours and reset modem if it has no GSM service at that time.

this helped me much. thank you. i will write the responses the next time modem will be hanged.

If the modem has no service from its “home” operator, it may be in “emergency calls only” mode with another operator - in which case that was the signal strength for the other operator.
That’s why you also need to check AT+CREG and AT+COPS.

Alternatively, enable +CREG unsolicited responses - and monitor them.
Also check for +WIND: 7 and +WIND: 8
And take a look at AT+CCED…

Resetting the modem won’t help the signal strength!

What you really need to do is to take steps to improve the signal; eg,

  • If another operator has better service in that area, can you switch to that operator?
  • Can you reposition the unit?
  • Can you use a better antenna and/or shorter cable?

Hi awneil,

i have just seen your message because i wasnt informed by email so i didnt know that you posted a message.

I will try to catch +CREG unsolicited responses as you adiviced and i will look at AT+CCED command. You are right about signal strength values. But whenever i see a modem hangs, i just reset it and it starts to run again without any signal problem. Thats why i think of resetting modem if the modem has no service.

I can not change the unit position at those times. While it happens randomly, it is hard to find a better position. And i can not switch an other operator. I am curious about antennas. I use an antenna which has no cable. Maybe we can order better antennas but i have no idea about antennas. I mean i dont know which antenna is better and dont know how well my antenna is.

Your Wavecom distributor should be able to advise you about antennas - or, at least, recommend a suitable specialist…

The point is: modem is not hung - it is still operating correctly!

However, it does seem that these modems can get “lazy” - they have lost service from the “Home” network, and got emergency service only from another network, but they then don’t seem to try so hard to reconnect to the “Home” network.
On reset, it seems that they try “harder” to find the “Home” network; which is why your resetting them appears to “fix” it - but it doesn’t really, as the problem will just recur next time it loses service from the “Home” network.

I don’t know if this is specifically a Wavecom issue, or if all GSM devices would exhibit similar behaviour under the same circumstances :question:

Again, the root cause is poor signal; the only true fix is to improve the signal level - anything else is just a workaround or band-aid.

One thing you could try is to have your application detect when the modem loses service and, if it doesn’t recover within some reasonable timeout, force a reboot…

Thank you awneil.
I got the points you told. I will try to find the best fix for this issue. I will write the results here if i will get any.
Thanks again.