[cisco-voip] Nat skinny problem

[Mauro Celli]

Hi,
i have one lan with 30 ip phone and a remote cucm 6.1
Ip phone connect to cucm with a wan connection.
I need to make a source nat applied to my ip phone,in lan side router I have added this nat pool
ip nat pool Voce 172.21.3.2 172.21.3.254 netmask 255.255.255.0 type match-host
All work as expected but some times ip phone are disconnected and i need to reboot it.
The problem is only when i press the line button or when the phone is in idle,during communication all
is ok.
The time of problem is random,from 5 up to 30 mins.
Skinny works on tcp 2000, therefore is not a timeout problem (default 24h).
My ios is 124-24.T1 on 878 router.
Any ideas? Ps. Sorry 4 my English ;)