[Serusers] natpings disappear?

Hi all, I'm running ser along with rtpproxy and the nathelper module. My layout is as follows, I have a ser proxy running on the public Internet, and I have a bunch of UAs behind a nat firewall. I'm currently having the problem that UAs behind nats register successfully, and they can make calls to each other from inside and outside nat. At this point all looks great. I have been running the natping_interval at 30 seconds, and recently I have put that down to 5 for testing purposes. The following happens to all my UAs but I will detail just one. The UA registers with ser at 14:26:39 It receives an invite, which gets canceled and a bye/ok is completed at 14:27:30 UDP pings cease to enter the private network via the nat router at at 14:32:36 The UA re-registers at 14:56:37, and the udp packets start again, and the above cycle seems to be repeated. I can still make outbound calls after the udp pings stop, but I can't receive calls. I'm not sure if the udp pings are still being sent by ser, and they are getting dropped at my router. The routers I have been using; I have been using UAs behind a cheap D-Link router, which I later switched to a Cisco router, I have also had UAs behind two layers of NAT, and that also works great until the udp gets cut off. Has anyone come across this issue before? I will try and match my udp pings on both sides of NAT and try and see at what point the udp pings stop at, be it ser that stops sending them, or nat that just drops them silently or other. Any help is greatly appreciated, Thanks, -Jev modparam("nathelper", "natping_interval", 30)