R550 duplicating packets

[manelion]

I am using the R550 as a local access point with no connection to the Internet. I have written a Mac app that streams SDP messages and RTP/UDP packets over multicast via WiFi using the R550. I have verified the Mac only sends one packet at a time, and that the R550 is receiving and sending those packets along to another app I wrote running on my iPhone. But the R550 is duplicating packets, sending two packets for every packet it receives (confirmed by collecting and examining packet traces from the R550 itself - two packets being sent at the same timestamp). I have updated the R550 firmware to the latest version, and configured my R550 AP as follows:

disabled SmartMedia QoS

disabled directed multicast

set the qos directed threshold to 0

disabled qos mirroring

using the 5GHz radio only

set BSS minrate to 12

enabled OFDM only

set DTIM to 1

Even after all this, the R550 continues to duplicate packets. No duplication when I remove the R550 from the signal path entirely and hard-wire my Mac and iPhone together via ethernet cabling to the same network switch.

These are media apps that don’t tolerate such duplication. How do I make it stop? All considered thoughts and suggestions appreciated.

Cheers, Martin