iPhone using Cellular Data on Wifi

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I have an iPhone 6S with Wifi Assist turned off. I noticed in my cellular data usage (on iPhone AND on Koodo data usage) that I'm using a bit of cellular data when I'm on wifi. It was using Cellular data during the night while I was sleeping and definitely on Wifi.

What gives?
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Jerrrrrrr

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Posted 2 weeks ago

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MoFromTo2018

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Can it be possible that your WIFI is having issues and ends up disconnecting? You can put your iPhone on WIFI Calling and before sleeping, put your phone to Airplane with WIFI. I have a iPhone 6S and never had this issue. Maybe update the firmware of your iPhone, and also your router.

Also, turn off personal hotpost or change the password.
(Edited)
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Robert, Mobile Master

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I remarked the same thing during the night, but didn'T find a reason why this is happening. 
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Jerrrrrrr

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Note that I'm new to Koodo so that's why I noticed this. I was checking the data usage to make sure all is well after the switch from Telus.
I already updated my router an hour ago, so we'll see if that helps. Phone f/w the latest already.  And no hotspot.

I don't think it's dropping wifi though. It's a strong signal.  I also reset my network settings on the phones. I'll see if that helps too.
It's actually 2 phones doing the same thing. My wifes and mine. It's not a lot of data, but enough to annoy me.

So tonight, I'm turning my cellular data right off and leaving hers on. I'll see what happens.
I've read some stuff that says the wifi radio gets turned off when it goes to low power mode and it will use cellular during this. But that sounds bogus to me.
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David, Mobile Master

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“I've read some stuff that says the wifi radio gets turned off when it goes to low power mode and it will use cellular during this.”

This issue is sufficiently frequently reported to be believable. Considering most of the activity (calls, texts, etc) occurring during the overnight period would be a cellular activity, and that it takes time for Wi-Fi to connect when I enter a new area, I accept cellular data takes precedence.
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Jerrrrrrr

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Weird. Even with Cellular data completely off, it still used cellular data for system services. So far just Push Notifications. Anyway, I'll let it run over night and see what happens.
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Dennis, Mobile Master

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If the phone's data usage is reporting usage while your cellular data is off, I recommend bringing your device to the apple store.

Take screen shots of the data with cellular data off before and after to show the uncontrolled usage
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Jerrrrrrr

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Update from overnight monitoring. Installed new firmware in wifi router, reset all network settings in both phones, ensured both phones have good wifi connection throughout house..

Phone #1
- Cellular Data turned off completely.- Also before shutting off cellular data, removed a few apps from accessing cellular data. But that should have no effect since the entire thing was turned off.- More importantly, turned off notifications for some apps that I don't care about (under Settings/Notifications).- Data Usage went to ZERO overnight. So that's good.- I suspect it was turning off Notifications for some apps that stopped the Push Notifications from using data.- I just turned cellular data back on as I was writing this. I see it's used 0.4 MB for system services already. Push notifications.

Phone #2- Just updated Network settings.- Cellular Data on, no notification changes
- Still used some data overnight. < 1mb.- I didn't get a chance to view the data usage on the phone before it left for the day...I'm going to guess System Services of some sort.
So I guess there will always be data leaks with system services. Still investigating.
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Dennis, Mobile Master

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This is good testing. Definitely something to do with the phone unfortunately.
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Jerrrrrrr

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Still have to look at phone #2. It used 20mb just after 6am. Need to check that out. Because over a month that's 1gb, so that's not good. Might be able to tweak some settings. Definitely not willing to turn off Cellular data every night. That's a pain.

And it still annoys me that even with Cellular Data turned off, phone #1 was using cellular data before I did some tweaks to notification settings.

More to come...
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rikkster, Mobile Master

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Another option is to disable apps that use 'background app refresh'. This feature can be disabled completely, preventing all listed apps from using background data. This may not be a practical approach to some. The other option is to enable Wi-Fi only mode. Go through the app list and disable apps that don't require background app refresh, (e.g. third-party apps). Experiment by enabling just a few apps and monitor for mobile data consumption.

To get to Background App Refresh, go to: Settings > General > Background App Refresh

It's worth noting that background app refresh is enabled by default from the factory. Also, a system update or factory reset re-enables this feature. On a bit of a plus side, minimizing the number of apps that use background app refresh may help to reduce battery drain.
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Dennis, Mobile Master

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I have had background app refresh on and off, and honestly I cant tell the difference in app quality.  With either options I still get my notifications and updates like normal.  Because of that I always set this to off
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Jerrrrrrr

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Another small update.
Phone #1- Turned on Cellular Data overnight. Wifi on as well (always).
- It used about 0.5 mb of cellular data. Although, the only category measuring anything was Siri at 1.7kb. So some mystery data usage of about 0.5mb (thanks Apple).- This was the phone the used 0 bytes of data with cellular data off and just wifi the other night.

Phone #2- Cellular data and Wifi on overnight. The only change I did for it overnight was in the facebook and instagram apps. Turned off Autoplay of videos unless on wifi. So that will have no affect while sleeping...but still should help later.
- Used about 200K of cellular data. Mostly PUSH notifications through system services.- After talking to the wife about phone #2 from the first night, we figured the 20mb chunk was mostly actual facebook/instagram cellular data usage (while actually off of wifi).- Also. I just checked now, her data usage this morning (from the time she left home until lunch)  and it was way down. Went from 20mb to 2mb. So I'm guessing the changes we made to FB and Instagram helped. No use autoplaying video in FB on cellular. Most of that crap we scroll right by anyway.

So I'm willing to say:- Even with Cellular data switched off completely and wifi on, it's possible that the iphone will use cellular data for some system services. I saw that at first before I turned off some notifications..That's just annoying. Especially if you're trying to conserve at the end of a cycle and not go over.
- With Cellular Data and WIFI BOTH on, the iphone chooses to use Cellular data (instead of the fully functioning wifi) for some critical system services like push notifications. I'm not sure why SIRI uses it. I get why it does this. It's so the PUSH are truly PUSH and not relying on the wifi radio being on. Although, I'm still not 100% convinced of that theory (wifi radio off while sleeping). My iPad has no cellular and somehow it manages to get push notifications JUST FINE while it's sleeping away. As a matter of fact, I just sent a text to my wife and her sleeping ipad just dinged immediately after I pressed send.

So I guess that's it. I can live with <1mb of data use over night. Not worth shutting off cellular data for that.  But I'll definitely be tweaking all the app settings to reduce data usage as much as possible. I'd prefer that the iPhone completely uses wifi while it's available, but what are you gonna do.

If anyone has any further input on why the iphone uses cellular over wifi for system services, I'll gladly listen. Or how to avoid it without manually switching off cellular data every night.
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Dennis, Mobile Master

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That theory is only true when your phone is not plugged in. So just out of curiosity, when you go to bed and the data leakage occurs, do you plug your phone in? If not, give that a try
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Jerrrrrrr

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My theory holds so far. One was plugged in, the other not. Both used cellular data instead of wifi. I did see your old post (or someones) about if it's plugged in it won't use cellular over wifi. But that's not what I observed.
(Edited)
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Dennis, Mobile Master

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I think it's time to visit the apple store