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Mysterious iOS 6 Cellular Data Usage: A Deeper Look

It’s becoming more and more difficult to ignore the numerous reports that iOS 6 on an iPhone or iPad can use far more cellular data than iOS 5 or earlier systems did. Anecdotal evidence is hardly to be trusted, even when it arrives in large quantity, but surely a massive thread such as this one on the Apple Support Communities cannot consist entirely of people who are mistaken or misapprehending the phenomena. Moreover, some of us here at TidBITS are convinced that we’ve experienced the problem in our own lives.

In this article, which picks up on some themes already broached by Glenn Fleishman in TidBITS (see “What’s Behind Mysterious Cellular Data Usage in iOS 6?,” 29 September 2012) and in a Macworld podcast, I’ll try to distinguish several strands of the issue. But first, let’s agree on just why the issue is an issue. We can all accept, I think, the following two axioms:

  • Axiom 1 First and foremost, it’s all about money. For my iPhone, I pay $15 for the grandfathered-in minimal 200 MB per month cell data plan from AT&T. The penalties for exceeding this monthly limit ($15 for each subsequent 200 MB) are severe as a proportion of my monthly bill, and the penalties for exceeding it by a lot are really severe. Users are aware of this, and are careful in consequence. For my iPhone to cost me money gratuitously, beyond whatever control I can achieve through such care, is wrong.

  • Axiom 2 The expectation is that when your device has a Wi-Fi connection, as when it is sitting in your living room and can see your home network, it will use virtually no cellular data; all the data you ask for, such as fetching your mail or viewing a Web page, should come over Wi-Fi. I say “virtually” because some phone activities, such as checking your voicemail by way of the Phone app’s interface rather than dialing your voicemail manually, do require a cellular connection — but they use only a tiny amount of data. This expectation is both reasonable, because if it is violated there is a danger that you can exceed your data cap (see Axiom 1), and deeply ingrained, because that is demonstrably just how iOS 5 and earlier systems behaved.

With that said, it is clear that some of us at TidBITS have recently experienced cellular data usage in excess of our expectations or intentions, and that some users (as shown in the Apple Discussions thread I cited above, as well as in reader comments on Glenn’s article) have experienced cellular data usage massively in excess of their expectations or intentions. So something is going on. I think we can distinguish four broad themes in the gusher of information and speculation about this problem. By concentrating separately on these four themes, I hope to focus your attention on what you can do to stem the flow of unwanted and costly cellular data on your own device, until such time as Apple provides a system-level fix.

How To Measure — How do you know how much cellular data your device is using? In my opinion, a third-party app can’t tell you; it just doesn’t have access to the needed information. When I started seeing unusual cellular usage on my own device, I installed DataWiz; the interface is delightful, but the numbers proved to be sufficiently different from other forms of measurement that I eventually removed it. Similarly, Adam Engst swears by DataMan, but in the same breath adds all sort of caveats about making sure it’s running; DataMan Pro, which had the power to point the finger at individual processes using cell data, was removed from the App Store by Apple, although Adam and other early purchasers still have it.

In my view, there are only two numbers you should accept as meaningful. One is from the device itself, as reflected in the Settings app. Go to Settings > General > Usage > Cellular Usage. The numbers shown here are cumulative, so in order to know whether there’s been a sudden recent spike you may need to have made a note the last time you checked. But by deliberately pressing Reset Statistics on the first day of your monthly billing cycle, you can get a sense of whether you’re likely to exceed your cap this month. Of course, you have to know what day of the month that is, and it’s a pain to remember to do it; but the Calendar app can help you set a reminder that eases the pain.

The second important number — perhaps the only definitive one — is what your cellular provider says. After all, the real question is not how much data the iPhone thinks it’s using, but whether your provider is likely to charge you for exceeding your cap. You may be able to check your provider’s usage figures in an automated fashion. For example, on my iPhone, I go to Settings > Phone > AT&T Services, and am shown a number I can dial to View My Data and Msg (*3282#). Tapping that number causes a text message from AT&T to arrive in the Messages app, telling me when the next bill cycle starts and how much data I’ve used so far in this cycle.

Inspect Your Settings — iOS 6 introduces a lot of new settings, squirreled away in various places, enabling you to specify explicitly whether an app should be allowed to use cellular data, or implicitly whether some process should be allowed to communicate over the network at all (the implication being, if it wants to communicate when you’re in the field, it will certainly use cellular if it can). It is worth taking some time to walk recursively through all your settings, looking for those controls. This is a boring and tedious operation, but hey, we’re talking about your money here. The difficulty is compounded by the fact that the implications of a setting may not be obvious.

Before listing some of these miscellaneous settings, I must say something about the master setting at Settings > General > Cellular. There is a master Cellular Data switch at the top here, and I’m certain that it does what it implies: if you switch it to OFF, the cell radio is effectively turned off, and although the phone still works for voice, you absolutely positively can’t use any cell data under any circumstances. You are unlikely to want to use this switch, though, since it hampers your use of the device. For example, you can’t check your voicemail easily. Plus, having this switch turned off caused Find My Friends to fail to track me when I was driving to pick up Adam in North Hollywood last week (and caused his text message to me to traverse the SMS system rather than Apple’s free iMessage system). On the other hand, why was it off? Because my phone is using excessive cell data, and switching this setting to OFF prevents that! So it’s Catch-22.

Here are some other settings to notice. Observe that I have no special information about what they really do or what effect they really have on cell data usage; I’m merely suggesting that they might be worth toggling in order to try to keep cell usage down:

  • Settings > General > About > Advertising: I’m told that the Limit Ad Tracking switch can affect cellular use, and that to minimize such use you want the switch ON (because this will limit ad tracking, don’t you see).

  • Settings > General > About > Diagnostics & Usage: Tap Don’t Send to prevent behind-the-scenes communication of diagnostic information back to Apple.

  • Settings > General > Cellular: Scroll down to see several Use Cellular Data For switches. Clearly if you don’t want these processes using cell data, you should switch them OFF.

  • Settings > General > Date & Time: Switch Set Automatically to OFF, perhaps, though one hardly suspects time queries of using much data.

  • Settings > Privacy > Location Services > System Services: Set all of these to OFF, since any of them might try to “phone home” while you’re out in the field. Pay attention to the pointer icons next to each service, since they tell you which services are actually being used: purple icons indicate recently used services, gray icons appear next to services that have been used in the last 24 hours, and purple outlined icons appear next to services using a geofence.

  • Settings > Mail, Contacts, Calendars > Fetch New Data: Switch Push to OFF if you don’t want these three services trying to shove data at you when you’re out in the field. Personally, I also have Fetch set to Manually, so no communication can take place unintentionally. Even then you’re not finished, though; tap Advanced to move to yet another screen with yet more Push-related settings. Tap each service in turn to set it up. For example, I’ve set iCloud to Manual and my Mail accounts to Manual here as well; I do not understand why this advanced setting exists or how it can be allowed to override my Push and Fetch settings from the earlier screens, but I am taking no chances.

  • Settings > FaceTime: Set Use Cellular Data to OFF. Clearly a video conversation via FaceTime running over the cell data connection is going to be disastrously expensive.

  • Settings > Safari: Scroll down to see Use Cellular Data; switch it OFF. Note that this doesn’t claim to prevent Safari from using cellular data; it says merely that it prevents Reading List from syncing data via cellular. I’ll have more to say about this later.

  • Settings > iTunes & App Stores: Scroll down to see Use Cellular Data; switch it OFF. This actually applies, it appears, only to iTunes Match and automatic download of items newly purchased on other devices.

  • Settings > Music > Use Cellular Data: This switch appears only if you have iTunes Match turned on. Switch it to OFF to prevent iTunes Match from downloading music via cellular.

  • Settings > iBooks: Switch Online Audio & Video to OFF. (Not everyone may have the iBooks app.)

  • Settings > Podcasts: Although we can’t recommend Apple’s Podcasts app, it’s likely that lots of people have it. If so, switch Use Cellular Data to OFF, but note that it applies only to automatic downloads. More on Podcasts later.

There may be other significant settings I’ve failed to list here. The important thing is not the list itself, though, but the process. It takes a lot of hunting and pecking and scrolling to ferret out all these settings! It’s almost as if Apple didn’t want to you to find them, though it’s more likely that no one at Apple has given the problem any thought at all. Plus, some of them seem to duplicate others, so that, for example, you may think you’ve turned off automatic Mail fetching in one place, only to discover that it is still turned on in another. It’s a jungle out there.

The System Might Be Buggy — We come now to an area that is rather controversial and, more to the point, largely out of your control. It is, however, close to the heart of the matter. There is reason to suspect that iOS 6 may be violating Axiom 2: that is, that it uses cellular data even when you are home and connected to Wi-Fi. And it may be doing this despite any of the settings I listed in the previous section.

For example, one day recently I was using Mobile Safari to watch a YouTube video at home over Wi-Fi, and discovered later (by inspecting my usage, as explained earlier) that about half the data had apparently come over the cell radio. This is definitely not how I expect my phone to behave, and moreover there doesn’t appear to be any setting allowing me to switch off this behavior for Safari. Safari’s Use Cellular Data switch, which I mentioned earlier, claims to be confined to Reading List sharing across iCloud.

However, that switch was in fact ON at the time this YouTube incident occurred. Since then, I’ve switched it to OFF, and the problem has not recurred. (Nor have other members of the TidBITS staff been able to reproduce the problem, even with that setting ON.) Which leads me to the following speculative question: What if the label on this switch is incorrect and it doesn’t apply just to Reading List? In other words, what if setting this switch to ON somehow gives Safari license to use cellular data generally while on Wi-Fi? I’m not suggesting that this would be intentional on Apple’s part, but it could have something to do with the behavior I and others have witnessed.

And that, in turn, brings me to the most speculative point of this article. Please bear in mind that it is speculative! I have no facts and no hard data, and I’m not trying to spread uncertainty or rumor. But the truth is that during the beta-testing period for iOS 6, developers saw in Settings a switch that apparently allowed iOS as a whole to use cellular as a supplement to Wi-Fi even when Wi-Fi was present. So, let’s say, for example, that you’re watching a YouTube video, and that your home DSL, while decent, isn’t fast enough to prevent a pretty long delay before the video can start. iOS might, if this switch were set to ON, reason to itself: “Gosh, I could help this fellow out and start the video sooner by pulling some of the video down over the cell network.”

That switch is no longer present in Settings, so don’t bother looking for it. But what if — and remember, this is pure speculation — what if it was removed because Apple had decided this was such a great feature that they could just safely leave this setting turned ON behind the scenes? In other words, what if iOS 6 now deliberately and automatically uses cell data to supplement Wi-Fi, and you can’t prevent it from doing so?

In any case, even if Apple decided against leaving that switch turned ON when they pulled it, who apart from Apple can say that the code underlying that switch isn’t still present in iOS 6 in such a way that it could become active in certain situations? It is never safe to assume that developers always know how their programs will operate, especially when the heavy lifting is being done behind the scenes by the massive Cocoa Touch framework; and with something as complex as iOS, there are plenty of unexpected behaviors of which developers know nothing and for which they cannot be held responsible.

Some Apps Might Be Evil — Some apps, by their very nature, can require massive amounts of data transfer. These are exactly the apps that one would wish to be most stringent in their adherence to Axiom 2. If iTunes Match or the Podcasts app downloads an entire gigabyte of data, which can quite easily happen, one might argue that you have only yourself to blame if you deliberately initiate such a download when you’re out in the field; but when you’re home, you expect Wi-Fi to be used exclusively. I have just said, however, that I suspect the system of possibly using cellular even when Wi-Fi is present. Under those circumstances, such an app could be a disaster (that gigabyte of data would cost me something like $60, and we’ve heard reports of 8 GB of data — $240 — being downloaded without the user’s knowledge or intention).

But we can go further. Such apps may come with a Use Cellular Data switch in their settings, and you may have turned this switch to OFF. But what if the app fails to pay attention to that switch? This might be because the app has a bug, or it might be because of the speculative system-level bug I hypothesized in the preceding section. I do know, as a developer, that iOS 6 has a new developer-level feature where, when your app places a request over the network, it can specify whether or not that request may be satisfied using cell data. Well, what if that feature is broken internally at system level, so that I (the developer) believe I am turning cell data off for my app in response to you (the user) setting a switch, but in reality the system is using cell data anyway — and, perhaps, using it even when Wi-Fi is present? You can see that in that case we’d be in a pretty pickle.

There is no doubt that the Podcasts app and iTunes Match are in fact responsible for some of the very large cell data usage of which users are complaining. Recall that, as far as TidBITS is concerned, this entire thread started in an article by Glenn Fleishman (“Does Apple’s Podcasts App Suck Cellular Data?,” 17 September 2012) in which he observed cell data usage that he attributed to the Podcasts app. And this was before iOS 6 had shipped. The Podcasts app, of course, comes from Apple, so who knows what private system-level features (or bugs) it accesses behind the scenes? In any case, the Apple Discussion thread I mentioned earlier gives the impression that you can get massive cellular data use from the Podcasts app no matter how you set that switch.

Adam Engst, who still has DataMan Pro to give him some idea of which processes are using cellular data on any particular occasion, has made some further observations. He can demonstrate, for example, that the Skype app can use up to 2 MB of cellular data per day, just by existing in the background. And it can do that even when you’re on Wi-Fi. It’s not a lot, granted, but 15 to 30 MB of data out of 200 MB per month for just having launched Skype at some point seems excessive.

Another problem is that you don’t really know the meaning of the choices you’re making in an app’s settings. Adam has observed that the Podcasts app can suck down cellular data even when the Use Cellular Data switch is OFF, evidently because that switch applies only to automatic downloads of new podcast episodes, not manually initiated streaming. Assume, for example, that you have the first episode of a podcast downloaded, but not the second. When the first finishes playing, the second may start playing automatically, and even if it doesn’t, you might navigate to it using other audio playing controls, or even play it from the Podcasts app without noticing the little download icon. That’s a good way to use up tens of megabytes without noticing.

Conclusions — Although not every iOS 6 user is seeing a problem, there’s no doubt in my mind that a problem exists, and that the fix must come from Apple, possibly in conjunction with the phone providers. (Apple even implicitly acknowledged this with a carrier settings update for Verizon Wireless users that prevents the iPhone 5 from using cellular data while on a Wi-Fi network.) iOS 6 does use more cellular data than previous systems did, and it appears to use it in circumstances where previous systems did not.

A couple of days ago I restored my iPhone to a completely clean iOS 6 and went through all the settings I could find and turned everything off that might influence cell data use, except for turning off the master Cellular Data switch. Even though I was home with Wi-Fi the entire time, a couple of hours later, there had been some cell data usage. Even during the two hours it took me to draft this article just now, with my iPhone sitting unused beside me (except when I picked it up to navigate the Settings app so I could describe the location of the various switches), there was some rise in the reported cellular usage. These were not large amounts, but that’s not the point: the point is that the amount should be zero and it isn’t.

But this is not the worst. Reliable-looking experimentation has demonstrated that certain processes such as iTunes Match and the Podcasts app can download huge amounts of data over the cell network, even when you think you’ve told them not to. Glenn’s article referred to this very sane-looking, very scary blog post by John Herbert. Josh Centers has put up a video demonstrating that iCloud can leak cell data at the rate of 1 KB per second, even if every iCloud service is turned off. And, of course, clouds of witness have gathered at the Apple Discussion boards — the one I referred to at the start of this article, and this one, and doubtless many more.

Something must be done, and I have little doubt that it will be. If the posts at Apple Discussions are to be believed, users have not been hesitant to call their cellular providers and complain of unwanted cell data usage. The cellular providers, in turn, are surely talking to Apple. (And so too, I bet, are their lawyers. It wouldn’t be surprising to see a class action lawsuit against Apple with regard to these unwarranted charges.) In the meantime, if you’re having similar problems and can quantify and document them, I remind you that you can tell Apple about it at their iPhone feedback Web page.

Finally, Adam Engst (who, after all, publishes TidBITS and always gets the last word) encourages me to encourage you to request that Apple allow DataMan Pro to be sold in the App Store once more — even though I, Matt, think there’s a snowball’s chance of that happening, since to do what it does, DataMan Pro must surely be using undocumented APIs that the App Store explicitly excludes. Still, Adam has a point. What makes this problem so mysterious, after all, and so difficult to report clearly to Apple, is that most people who are experiencing it cannot identify which apps are at fault. While DataMan Pro may not be perfect, it provides precisely that information.

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