I did some tests regarding this issue and it seems that several Apple products are affected. The devices I tested are:
* Late 2013 MacBook 13" Retina
* iPad Air 1
* iPhone 5s
All of them show fluctuating ping times between 20ms and 300ms, but only if they are pinged. If I ping a non-Apple device from an Apple device the times are normal below 4ms.
The scenarios I tested:
ThinkPad -cable-> AP -wifi-> Apple-Device == fluctuating pings
Apple-Device -wifi-> AP -cable-> ThinkPad == constant pings
Nexus 5 Wifi Hotspot -wifi-> Apple-Device == fluctuating pings
Though I tried different APs the last scenario shows that the AP has no influence on this issue because there is no AP in that scenario 😉 Also, pings are only fluctuating in the direction of the Apple device.
My guess is that Apple puts its wifi modules in some kind of energy-saving mode causing them to receive packets only at certain time frames. Another test backs up my assumption, use the following command:
ping -c50 -f IP-of-apple-device
The first packet shows a high delay, but all following packets are very very fast, as they should be. Hence, as soon as we receive a packet we wake from energysaving and can handle further packets immediately.
Unfortunately, I have no solution for this problem as only Apple can change their wifi implementation. Nevertheless, I hope I brought some light in the dark 🙂
Cheers,
Nico
Edit:
Try this: ping -c50 -i 0.2 IP-of-apple-device
And vary the 0.2 value. This is the delay between consecutive pings. For me, 0.2 is OK, but 0.4 already yields fluctuations.
