Daniel Eran Dilger
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The Inside Deets on iPhone 2.0.2 and Dropped Calls

Daniel Eran Dilger
The mysteriously terse synopsis of the improvements made in iPhone 2.0.2, listed only as “bug fixes,” didn’t shed much light on why Apple’s Jennifer Bowcock could tell USAToday that “the software update improves communication with 3G networks.” However, our source close to AT&T helped illuminate why the update was necessary, what the problem was, and why the update didn’t immediately impact users equally.
The iPhone 2.0.2 update “fixed power control on the mobile,” the source told RoughlyDrafted. UMTS, the technology used to deliver AT&T’s 3G network, refers to phones and other client devices as “UE” for user equipment, and the base transceiver station towers as “Node B.”

Why the iPhone 3G dropped calls.

“In UMTS,” the source said, “power control is key to the mobile and network success. If the UE requires too much downlink power then the base station or Node B can run out of transmitter power and this is what was happening. As you get more UEs on the cell, the noise floor rises and the cell has to compensate by ramping up its power to the UEs.”

“If the UE power control algorithm is faulty then they will demand more power from the cell than is necessary and with multiple users this can cause the cell transmitter to run out of power. The net result is that some UEs will drop their call. I have seen the dropped call graphs that correspond to the iPhone launch and when the 2.0.2 firmware was released. The increase in dropped calls,” the source said, were the result of “dropped calls due to a lack of downlink power.”

Why the iPhone 3G suffered poor data throughput.

“The power control issue will also have an effect on the data throughput, because the higher the data rate the more power the Node B transmitter requires to transmit. If the UEs have poor power control and are taking more power than is necessary then it will sap the network’s ability to deliver high speed data.”

“This is one of the reasons why AT&T has been sending text messages to users to persuade them to upgrade to the 2.0.2 software. In a mixed environment where users are running 2.0, 2.0.1, and 2.0.2, the power control problems of 2.0 and 2.0.1 will affect the 2.0.2 users.”

“It is not the network that is fault but the interaction of the bad power control algorithm in 2.0 and 2.0.1 software and the network that is at fault. The sooner everybody is running 2.0.2 software the better things will be. Having seen the graphs the 2.0.2 software has already started to make difference.”

That explains why some users saw no immediate impact after installing iPhone 2.0.2, and why tests of individual iPhone 3G models showed no significant difference between the 2.0 and 2.0.2 software: the problem was only evident when a critical mass of phones all acted in concert to run a given cell tower out of power. This also explains why users in locations such as San Francisco and New York were seeing bigger problems than users in less densely populated areas where fewer iPhone 3Gs were in use.

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  • Brau

    Aha! So that’s why Roger’s has been calling me a few times each day over the last week! Oddly enough, every time they called … the call was dropped. LOL! I had to Google the number to find out who it was. I was lamenting to my wife that a cell company should at least be able to make a call without it dropping out; essentially blaming Roger’s. I upgraded my iPhone today so hopefully it will have a positive effect soon.

    Thanks for the explanation, Daniel.

  • Scott

    @ Brau, thanks for updating your iPhone, bit late but thanks anyway.

    To the rest who are still to update their phones, may you please update your iPhones now so we can all move on.
    And when iPhone 2.1 is release in September may you all please do the right thing and update the phones all at once. Enough of the bad publicity already!

  • Brau

    A bit late?!! I sync it every day but just got the upgrade notice today and installed it right away.

  • Jon T

    Thanks for this brilliantly concise answer to this baffling issue.

    Bit of a shame for all those iPhone doom-sayers out there!

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  • Dafydd Williams

    Please thank your source for us, Daniel, and thanks for a concise and much-needed update.

  • jecrawford


    Who is responsible for the power control software on the UE?

    Is there some software at Node Bs that contributed to the problems?

    Thanks for the logical explanation which should help dampen the hysteria. Unfortunately, damage has been done to both AT&T’s and Apple’s reputations.


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  • harrywolf

    Interesting that iTunes only told Brau about the update today – is that settings thing or what?

    I am on Rogers in Canada and have had the update for – what – 10 days?

    Maybe for the iPhone, Apple should ‘push’ the update if it really is this vital that everyone upgrades…

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  • HCE

    I’m not too sure I entirely buy this explanation. If this is just a case of the cell towers getting overloaded, everyone (whether they are using the iPhone or not) should be affected. I have seen a lot of people say that other 3G phones were working fine while the iPhone was giving trouble. I don’t know if that is true but if it is, it would cast doubt on your explanation.

    – HCE

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  • thomast

    So what this means is that an “appropriately” programmed phone or phones could possibly be used to mount a denial of service attack. They would need to suck up as much transmitter power as possible, and repeatedly redial when dropped. I wonder what the minimum number of phones would be to significantly impact tower performance?

    The design sounds fishy.

    So here’s an interesting question. What could be done at the design level to avoid this problem?

  • Brau

    “Unfortunately, damage has been done to both AT&T’s and Apple’s reputations.”

    Unfortunately I have to agree. Instead of asking me how I like the iPhone, many people are asking me about the battery life or other problems they’ve heard about in the media. The well publicized roll-out debacle, baselessly asserted battery life concerns, crashing apps, dropped call issues and the latest hack to bypass the lock code are having an effect. Apple is treading in dangerous territory where a fantastic device could be falsely seen as a failure/liability in the general public’s view. All the TV ads showing it off may amount to nothing if too many buyers approach it with a jaundiced eye.

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  • http://www.roughlydrafted.com danieleran

    @thomast: “So what this means is that an “appropriately” programmed phone or phones could possibly be used to mount a denial of service attack. The design sounds fishy. What could be done at the design level to avoid this problem?”

    Yes, that’s why regulators don’t allow open source DIY baseband cellular devices. Even the supposedly “open” cell phones are really just a regulated proprietary radio connected to a computer running linux on the front end. And that’s what “they’ve” done to solve the problem.

    That’s why we have laws relating to radio use, and why all devices have to meet standards in every country.

    You might also say, “an appropriately drunk driver could smash his 2 ton vehicle into other drivers and kill a bunch of people. what can be done to stop this?” Everything and nothing.

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  • thomast

    Heh. I’m afraid the drunk driving analogy doesn’t follow. A drunk driver who kills people is very likely going to be walking for the rest of their life. The reason is because we have police, and courts, and witnesses — not just victims. It sounds like the cell network isn’t policing itself. It’s allowing itself to be trounced again and again and again by errant phones.

    But is this really true? Let’s be *very* specific. Question: Will a set of cell phones with bad power management affect the performance and dropped call rates for phones that *do* have good power management? Or, will those “bad” phones only affect themselves?

    The article implies that “bad” phones can affect “good” phones. If that is true then my statement stands. The design is fishy, without adequate reprimands for those abusing it.

    But, of course, identifying “good” and “bad” phones may be hampered by wheat and tares problems, and that may be why this hasn’t been addressed yet.

  • http://www.roughlydrafted.com danieleran

    No I’m saying there are laws in place to try to prevent people from running over others. That doesn’t stop crime, and it doesn’t stop interference. Once you see the problem, you can take some efforts to address it.

    Are you asking if a device that isn’t working properly can have ill effects on other devices? Yes. That’s why I made the analogy to drivers. You don’t have to be drunk to be killed from drunk driving.

    If a company sold unlicensed gear that was intentionally contaminating the airwaves, they would be stopped and fined.

    Handsets always have bugs and problems. The source noted that Apple’s iPhone advantage is that Apple can roll out a fix and get it widely installed within days. Other manufacturers/operators sometimes have to track down users and ask them to come in for a phone swap to get new firmware on their phone.

    “[iTunes’] infrastructure allows Apple to do something that other mobile vendors can only dream of. Yes Apple may have dropped the ball with the release of the 2.0 and 2.0.1 software, but at least they can fix it pretty quickly. Software bugs on certain other mobile devices have caused us to track down their owners and get customer services to phone the customer requesting that they visit an AT&T store. When they visit the offending device is swapped for a new one
    with updated firmware.”

    To read more about UMTS power control:


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  • gus2000

    If I wanted to launch a DOS attack against cellular service, I wouldn’t need a gaggle of hacked phones. One 1900MHz transmitter and a white noise generator should do the trick.

    When a Node B needs to drop calls, I suppose the algorithm could choose the longest call, or the caller with the cheapest plan. But when you’re running out of power, doesn’t it make the most sense to drop the device that’s asking for the most power?

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  • Karl Gretton

    The issue with UMTS and dropping calls is well known, understood and documented. The iPhone is not the first device to have these issues – high-end Nokia’s, the new BlackBerry Bold, etc, all have the issues.

    Indeed, if you look at the stats on 3G capabable phones registered with a 3G profile in the HLR, only 10% of calls were completed via 3G around 2 years ago on European 3G networks – whether they had 3G turned off or because of network issues. Today the figure is still less than 50% inspite of the network operates spending hundreds of millions of € on optimizing the network.

    Power control is a critical issue in a 3G network. It isn’t purely the iPhone itself but the complex combination of devices using a set of cells. The way the network is ‘breathing’ at a particular location, etc.

    Yes, Apple can ‘tweak’ the iPhone to behave better when very high densities of devices are fighting for the same network resources and it has the luxury of an ultra-efficient update system, unlike any other device.

    Ultimately, AT&T needs to spend time optimizing its network, adding bandwidth and installing new cells in areas of high population density.

  • jmmx

    @ jecrawford and brau

    “Unfortunately, damage has been done to both AT&T’s and Apple’s reputations.”

    ATT already has plenty damage. :)

    As for Apple and the iPhone, it will all pass. As the service improves (as hopefully it will) users will let people know that they love the device. All will pass.


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  • Realtosh

    @ brau

    Your concern about quality is not unfounded. The Newton was a technical marvel ahead of its’ time. The initial technical issues of the Newton, especially the hand-writing recognition software, gave a great product a black eye that lasted past the corrections of the early glitches.

    I don’t think the iPhone will have the same problems. First and foremost, Apple is doing everything humanly possible to fix these recent examples uncharacteristic sloppy execution. MobileMe has had lots of focus as I’m sure that any technical issues with iPhone 2.0 will have the intense priority of a company that will be growing the iPhone into one of its’ larger businesses.

    The big reasons that these initial growing pains will not have long lasting effects, besides that they are geting fixed, are twofold. 1) The iPhone is the greatest phone ever made. 2) Apple will sell millions of them this holiday season.

    The sales of iPhone units will be limited only by the number of units that Apple will be able to get out of production through late November/ early December. I predict that Apple will have to airship large quantities of iPhones late in the holiday season to create some supply in an environment of frequently selling out most iPhone product. This last minute rush shipping will follow one of the fastest ramp ups of production in the history of mobile phones; certainly unprecedented in the smart phone space.

    So the point is that there will be lots of iPhones out there. Being the best phone ever made, it will speak for itself. Apple will blow away all estimates of iPhone sales.

  • http://aviflax.com/ Avi Flax

    “It is not the network that is fault but the interaction of the bad power control algorithm in 2.0 and 2.0.1 software and the network that is at fault.”

    I call bullshit. This may be technically caused by the phones requesting too much power from the base stations, but, you know, the base stations could be smarter about responding to those requests, and allocating their resources. In fact, rolling out upgrades to the base stations would fix the problem even if no iPhone users upgraded.

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  • thomast

    Daniel, thanks for the clarification, and as always, good job with your articles. In the end, as pointed out by gus2000, there are much easier ways to cause cell phone denial of service, so my comments were just a tempest in a teacup.

    As for Apple’s reputation, perceptions can be quite delicate. However, as you said, the fact that Apple can update the phone’s software easily to correct problems certainly dampens any bad feelings.

  • JohnWatkins

    The “power management algorithm” sounds like a pretty low level piece of code. Plus it is referred to as an “algorithm” rather than as “software” or “code” (although it does say “firmware”.)
    This makes me wonder if it is an algorithm that Apple engineered or if it is simply a recipe that that ATT or ATT’s equipment suppler recommended or spec’ed and that Apple used to create the code.
    If so it should show up on all phones on the network.
    Possibly it is a problem with all phone but only apparent on the iPhone because of its heavy use? If so, shouldn’t we have sen more problems on other phones?

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