Jezza 1685

Q: Why does Apple Push Notification Service (APNs) use Cellular/Mobile Data over Wi-Fi

I have been looking around and found these Apple support pages and they mention that iOS devices will use the Cellular data connection over a Wi-Fi connection for the Push Notification Service.

https://support.apple.com/en-us/HT203609

https://developer.apple.com/library/ios/technotes/tn2265/_index.html

For example the port that is used (5223) is open on our router but I noticed my iPhone says it is almost always connected to that via Cell but not very often via Wi-Fi.

Is there a reason that if it can successfully connect to APNs via Wi-Fi why it still maintains a Cell connection with the service as well?

 

Thanks!

Posted on May 4, 2015 7:43 AM

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Q: Why does Apple Push Notification Service (APNs) use Cellular/Mobile Data over Wi-Fi

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  • by ChrisJ4203,Helpful

    ChrisJ4203 ChrisJ4203 May 4, 2015 7:56 AM in response to Jezza 1685
    Level 9 (58,962 points)
    iPhone
    May 4, 2015 7:56 AM in response to Jezza 1685

    Just a guess, but I would say that it has to do with the Wi-Fi going to sleep when the phone goes to sleep. In other words, since the Wi-Fi connection is not maintained when the device is in sleep mode, to receive the push notification, you need to get it via cellular. That wakes up the phone, and causing it to reconnect to Wi-Fi, and would enable you to receive the rest of the message or other data.

  • by Jezza 1685,

    Jezza 1685 Jezza 1685 May 4, 2015 7:56 AM in response to ChrisJ4203
    Level 1 (9 points)
    Mac OS X
    May 4, 2015 7:56 AM in response to ChrisJ4203

    Yeah that would make sense for a constant connection, usually my iPhone will stay connected to Wi-Fi unless it's under 10% in battery.

    But if you leave a Wi-Fi area it would then have that 'always on' Cell connection to the Apple push service.

     

    Thanks!

  • by Lawrence Finch,

    Lawrence Finch Lawrence Finch May 4, 2015 7:59 AM in response to Jezza 1685
    Level 8 (38,093 points)
    Mac OS X
    May 4, 2015 7:59 AM in response to Jezza 1685

    WiFi on an iPhone always turns off 30 seconds after the phone goes to sleep. It has nothing to do with the battery state of charge. The reason is that the WiFi protocol uses power continuously, whether data are being transferred or not, so if it stayed on it would run down the battery.

  • by Jezza 1685,

    Jezza 1685 Jezza 1685 May 4, 2015 8:05 AM in response to Lawrence Finch
    Level 1 (9 points)
    Mac OS X
    May 4, 2015 8:05 AM in response to Lawrence Finch

    I don't agree with this because when I use AirPort Utility to see connected devices it shows my iPhone and all the rest of my families' iOS devices connected, even if they are in sleep and not plugged in.

    And also I have noticed when they are lower on battery the Wi-Fi icon will flash back up when you wake the device up.

  • by ChrisJ4203,

    ChrisJ4203 ChrisJ4203 May 4, 2015 8:07 AM in response to Jezza 1685
    Level 9 (58,962 points)
    iPhone
    May 4, 2015 8:07 AM in response to Jezza 1685

    As Lawrence says, and I stated in my post, your Wi-Fi does not stay connected. It turns off as a battery saving measure, but connects again as I stated earlier. As much as you may think it stays connected, it powers down until you wake up the phone. If you are looking after waking it up, that is why you see the Wi-Fi fan.

  • by Lawrence Finch,

    Lawrence Finch Lawrence Finch May 4, 2015 8:10 AM in response to Jezza 1685
    Level 8 (38,093 points)
    Mac OS X
    May 4, 2015 8:10 AM in response to Jezza 1685
    • Go to Settings/WiFi and note the IP address of the iPhone
    • Open a Terminal window on your computer and enter "ping    <phone's IP address>"
    • Put the phone to sleep
    • After approximately 30 seconds the one second ping responses will start to time out
    • Wake the phone and the responses will resume
  • by Jezza 1685,

    Jezza 1685 Jezza 1685 May 4, 2015 8:14 AM in response to ChrisJ4203
    Level 1 (9 points)
    Mac OS X
    May 4, 2015 8:14 AM in response to ChrisJ4203

    I have read on another threat on older iOS versions (could be in newer versions too) that if Cell data is on it will always use that, but if you have Cell data off it will keep Wi-Fi active all the time.

    Not really sure unless Apple answered exactly.

  • by Jezza 1685,

    Jezza 1685 Jezza 1685 May 4, 2015 8:16 AM in response to Lawrence Finch
    Level 1 (9 points)
    Mac OS X
    May 4, 2015 8:16 AM in response to Lawrence Finch

    Yeah thanks I have actually done this exact test before, after about that time it will timeout, but that could just be the device blocking out any other traffic (such as the pings) for security and/or saving battery.

  • by Lawrence Finch,

    Lawrence Finch Lawrence Finch May 4, 2015 8:22 AM in response to Jezza 1685
    Level 8 (38,093 points)
    Mac OS X
    May 4, 2015 8:22 AM in response to Jezza 1685

    Do the same test and you will see that WiFi still goes off after 30 seconds. Why would the phone decide to block WiFi? It doesn't make any sense.

     

    Anyway, you can test it another way. While the phone is asleep with WiFi on and cellular data off send an email to a Push account and see if you get a notification.

  • by Jezza 1685,

    Jezza 1685 Jezza 1685 May 4, 2015 8:34 AM in response to Lawrence Finch
    Level 1 (9 points)
    Mac OS X
    May 4, 2015 8:34 AM in response to Lawrence Finch

    No I mean, iOS might be set to block out any traffic except a specific set after a certain amount of time, on battery.

    Because wireless routers pick up that the devices are still connected while in sleep, I have not just seen this on AirPort Utility at home.

     

    And yes I have tried that before, and received the email push notification on an iCloud account.

  • by chattphotos,

    chattphotos chattphotos May 4, 2015 9:11 AM in response to Jezza 1685
    Level 4 (2,442 points)
    Desktops
    May 4, 2015 9:11 AM in response to Jezza 1685

    APN is a standard acronym for Access Point Name, not Apple Push.

     

    Plug the phone in if you want push notifications on wifi.
    Otherwise turn the notifications off, they only use about 15MB each month, so its not a significant data impact...


    Here's the access log of my iPhone, it doesn't block traffic, it disconnects from the AP.

    Screen Shot 2015-05-04 at 11.00.39 AM.png

  • by Jezza 1685,

    Jezza 1685 Jezza 1685 May 4, 2015 9:17 AM in response to chattphotos
    Level 1 (9 points)
    Mac OS X
    May 4, 2015 9:17 AM in response to chattphotos

    No, 'APNs' stands for Apple Push Notification Service

    http://en.wikipedia.org/wiki/Apple_Push_Notification_Service

     

    And it's not exactly an issue, I read they have a max limit of 2KB per notification on iOS 8 now.

     

    I was just wondering why it doesn't use Wi-Fi like all other services that switch over to Wi-Fi as soon as you have a connection to it.

  • by Jezza 1685,

    Jezza 1685 Jezza 1685 May 4, 2015 9:19 AM in response to chattphotos
    Level 1 (9 points)
    Mac OS X
    May 4, 2015 9:19 AM in response to chattphotos

    And why do the Wi-Fi routers I have used before, including AirPort Extremes, Expresses and Netgear routers display that iOS devices are still connected in sleep on battery?

  • by Lawrence Finch,

    Lawrence Finch Lawrence Finch May 4, 2015 9:23 AM in response to Jezza 1685
    Level 8 (38,093 points)
    Mac OS X
    May 4, 2015 9:23 AM in response to Jezza 1685

    They are not displaying connectivity. They are displaying devices that have leases on an IP address.

     

    Look, this has been discussed ad infinitum for over 7 years in these very forums. WiFi turns off when the phone goes to sleep. That is a fact. Your wanting it to be different will not change that. Your imagining that it is different will not change that.

     

    There's no point in continuing this discussion.

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