[Serusers] call between two NATted ATAs - is it possible ?

Hello! I'm interested to implement the possibility of call between two NATted ATAs using SER 0.8.10 and Maxim's nethelper module. I'm using config described at http://lists.iptel.org/pipermail/serusers/2003-January/000165.html Signalling works just fine, but no media stream. My test setup: ATA1 --- NAT1 --- SER --- NAT2 --- ATA2 cut from tcpdump of call from ATA1 to ATA2 on private side of NAT1: 213.186.192.26 is NAT2 23:52:05.707635 213.186.192.26 > 172.20.0.205: icmp: 213.186.192.26 udp port 16384 unreachable [tos 0xc0] 23:52:05.727178 172.20.0.205.10000 > 213.186.192.26.16384: udp 32 [tos 0xa0] 23:52:05.727677 213.186.192.26 > 172.20.0.205: icmp: 213.186.192.26 udp port 16384 unreachable [tos 0xc0] 23:52:05.747216 172.20.0.205.10000 > 213.186.192.26.16384: udp 32 [tos 0xa0] 23:52:05.747734 213.186.192.26 > 172.20.0.205: icmp: 213.186.192.26 udp port 16384 unreachable [tos 0xc0]