iPhone WiFi Connection breaks frequently – No Fix? (UPDATED)

Posted under A Geek Dad's Life, Blog Posts

UPDATE 2010-10-20: Our fix was to replace the wireless access point and the router with a new Netgear WNR2000 WiFi Router. We were lucky that we were able to use that old Linksys equipment for 6 years before it was obsolete.  (I mean, come on, the old devices still said “Linksys” on them.)

Now, on to the old story as if it were new…

Our iPhone WiFi connections will frequently stop working even though the WiFi symbol remains visible in the iPhone’s status bar.  We suspect that there is some janky business happening when our iPhones toggle between the cell network and our local WiFi network during the phones’ sleep/wake cycles, as well as at other times.

Nothing we have tried has fixed the problem.  Our next step will be to buy new networking gear, but we have no guarantee that will fix anything. The “fix” that has worked best for us is to try to keep the iPhone WiFi connection alive all of the time, and those settings are described here as well as in this blog post.  If you want to know more about our journey and to see if our problem matches yours, read on…

The Problem

We have two iPhones; an old iPhone 3G and a new iPhone 4.  We have been fighting WiFi connection problems for two years and I thought that the new iPhone 4 would do a better job of remaining connected to our WiFi network.  Nope.

The phones’ WiFi connection will stop working even though the WiFi symbol remains visible in the iPhone’s status bar.  It can happen anytime, even if the phone does not go to sleep.  It can happen during heavy usage or no usage at all.  The only two things that get it working again are:

1. Deactivate/Reactivate the WiFi connection on the phone
   –or–
2. Power cycle the wireless access point (WAP)

Can you hear me now?  ZZZZZZzzz

We do seem to notice the problem more frequently after the phone wakes up from sleeping (when the screen is dark and you click the home or power button momentarily).  When the phone wakes up, it usually shows the 3G symbol, and then shows the WiFi symbol a few seconds later as illustrated in the screencaps below.  More often than not, the WiFi connection will not work even though the symbol is visible and the signal strength is excellent.

I used WireShark to monitor the wired network between the WAP and the router and saw when the traffic stopped.  The last traffic I see are packet retries from the foreign system (Facebook, Gmail, etc), presumably because the iPhone initiated the conversation and then disappeared from the network. There is no traffic coming from the iPhone, but my other WiFi devices continue to work properly during this ‘outage.’

What Didn’t Work (though still might help)

Our gear:

• iPhone 4 with OS v4.1 (8B117) modem firmware 02.10.04
• iPhone 3G with OS v3.2
• Linksys BEFSR41 Router v4.3 with firmware v2.00.4
• Linksys WAP54G Wireless Access Point v1.1 with firmware v1.09

We have tried or verified the following (in order), each time rebooting the access point and toggling the iPhone WiFi off/on:

1. Set the wireless access point’s SSID to a unique name.
2. Setting WPA with AES (with a complex 63-character password)
   (Note: we also use MAC filtering on the WAP.)
3. Ensuring that no other nearby access points share the same channel as mine.
4. Setting static IP and DNS on the phones’ WiFi connections
5. Raising screen brightness (yeah I know, right?)
6. Disabling Bluetooth
7. Disabling "Ask to Join Networks"
8. Change the Advanced Routing as suggested here, reboot the WAP, toggle the iPhone WiFi on/off
9. Resetting the Network Settings on the iPhone
10. Lastly, we changed the Advanced Routing AGAIN, this time according to Nat Julian Belza’s recommendation, specifically the lower DTIM interval.  It was set at 50 based on another recommendation from someone else. I chose to set it back to the default “3” instead of recommended “1".
    Setting the DTIM interval lower has the effect of preventing the iPhone’s WiFi radio from going to sleep in the presence of multicast traffic.  Honestly, I’d prefer to allow my iPhone WiFi radio to sleep in order to preserve battery life, but I have to go with what works. 

Close, but no cigar

While that last step #10 above seems to help the connection work better, it does not appear to solve the underlying problem.  I still have to toggle the WiFi connection off/on several times a day.  It’s maddening.  Short of blindly buying new networking equipment, we are out of ideas.

Speculation

I suspect that there might be some janky business happening when the iPhone toggles between the cell network and our local WiFi network.  If I had a $200 AirPcap device, I would know for sure. 

It’s a tricky bit of engineering to route network traffic properly between two disparate, heterogeneous, and intermittently-available networks.  Without knowing more, I would hazard a guess that the iPhone’s network stack is hung awaiting a reply/ack from the wrong network, or the phone’s wifi queue is deadlocked, or the phone’s handshake is corrupting something in the wireless access point, or some other such nonsense.  It is most definitely specific to the iPhone’s software, regardless of whether or not the actual failure is occurring in the phone itself.  Our other wireless devices (three laptops and two handheld game devices) all work fine.  And, yes, we had them powered off during these tests.  We only had the iPhone 4 on while troubleshooting.

Help?

If your iPhone’s WiFi connection works without fail ALL of the time, what kind of access point do you have?  We’re We were looking for a stand-alone WAP, not an all-in-one WAP/Router combo but we changed our minds.  You are not crazy.  There is was a problem.  Maybe this information will help you. 

(UPDATE 2010-10-20: We ended up buying a Netgear WNR2000 WiFi Router. 17 hours into it, it is working like a champ.)