Wireless I/O graph-- What this pattern means? Why consistent timeouts?

[jonathan.maxwell]

Hello.

Please see 2 images attaches-- I/O graph, and pcap.

QUESTIONS:

1. What does this specific pattern in this wireless I/O Graph represent?

2. Why does wireless device exchange no packets for approximately 1.5 seconds in a repeating pattern?

Any helpful input is appreciated.

Additional information: This may not be relevant to the graph (because after research I expect the symptom is a documented bug involving Apple security protocol implementation.): Client is experiencing symptom that only Apple vendor devices are being randomly disconnected from 1st SSID of multiple SSID wireless network.

WLC= C9800-40-K9, AP= C9120

I look forward to your input. Thank you.

[MHM Cisco World]

if only APPLE then there is high chance that you need enable Fast transition.
https://www.cisco.com/c/dam/en/us/td/docs/wireless/controller/technotes/80211r-ft/b-80211r-dg.html

[ammahend]

This does seem like a buggy behavior, this can not be contention, time is too long, if you have QOS enabled and high number of devices using wireless medium preferably then it’s possible to see such pattern but again 1.5 sec seem to long and I am not sure you are using 802.11e heavily. 
what’s the effect of this ? Are you seeing degraded performance on these devices ?

have you compared the graph with any other non-apple device ? 

[Rich R]

What version of software is your 9800-40 running?

[Arshad Safrulla]

How PCAP was done?