[Serusers] NAT ping and consumer router

Hi, Does anyone know and use a consumer router which works with NAT ping? I did some research recently and can't find any. Basically if a phone is behind NAT, we need to keep the NAT binding in the router active even if there is no activity from the phone. NAT ping from ser (either rtpproxy or mediaproxy) tries to ping the phone with an empty SIP packet. However this inbound UDP packet can't always keep the NAT binding active because some NAT firewalls ONLY refresh the timer based on outbound packets. So the result is that the binding expires after a certain time even if NAT ping is enabled. For example, Dlink falls in this category. It appears the timeout is 3 minutes and NAT ping won't make it active. If anyone has a good experience with any consumer router, can you please let share with us? Thanks, Richard P.S. There is a good rfc draft discussing NAT binding behavior, if someone is interested. http://www.ietf.org/internet-drafts/draft-audet-nat-behave-00.txt.