Wireless Latency in Apple iPads

[UnkeptBedroom]

Hello,

We've recently noticed the response time for iPads is higher than other clients on the same Wi-Fi network. Client --> Performance --> Scroll to Average Wireless Latency, and nearly every iPad we've looked at has spikes in its response times. I believe the graph usually ranges from 0ms to 80ms, but for an iPad it ranges from 0 to ~600-700ms, with spikes reaching up to the upper fairly consistently. Save for a few iPads, this appears to be the case for nearly every iPad we have, in every network, across Meraki organizations. Has anybody else noticed this?

[BlakeRichardson]

@UnkeptBedroom There is a good chance that this is happening when the devices are asleep and it's affecting the overall average. MacOS devices even when they are asleep are still active on the network, if you ping a device thats asleep you get very large ping times i.e. 300-800ms

This is me pinging an iPad thats asleep

[UnkeptBedroom]

Thank you for your reply! That would explain what we are seeing. A little more context - they were saying it was taking them a long time to upload photos through one of their apps. I will test to see if response times are normal when the iPad is in use, and let you know.

[PhilipDAth]

WiFi devices have two main modes of operation:

• CAM - Constantly Awake Mode.  The WiFi NIC is permanently powered up.  It has the highest throughput and the lowest latency.
• PSP - Power Save Polling.  The WiFi NIC turns on and off regularly (say every 100ms).  The AP buffers all the WiFi clients traffic in this mode, and only delivers it when the WiFi NIC polls for the traffic.  Muhc lowe throughput, latency jumps all over the place, but the battery life is much better.

Your iPads will be operating in PSP mode.

[UnkeptBedroom]

Thank you for your reply! Do you know if there's a way to force an iPad to operate in CAM mode?

[PhilipDAth]

Google found a lot of people having the same issue, but I did not see any consistent set of answers on how to address it.

[BlakeRichardson]

I don't think this is something that can be adjusted as it would affect battery life but also could mean that if the device is put inside a backpack and it's still transmitting at normal rates it could get hot and become a fire hazard. 

[PhilipDAth]

Typically, you wouldn't see transmit power levels over 100mW (if it was cranking).

Your hands generate more heat than this. 

[BlakeRichardson]

Was more thinking if Wifi is still active then device is more likely to continue background tasks including things like photo syncing which do make devices warm.