The second NAT SIP extension causes high latency


My Asterisk server (v1.4.26 CentOS 5 RPM) is outside the NAT using public IP and the SIP Extensions are inside the NAT.

The definitions of the SIP extensions in sip.conf are:

When the first SIP extension is connected everything works fine and the latency is 40 msec.

But when the second SIP extension is connected the latency of both extension’s drop to 2500 msec! and there is heavy network traffic (for example the echo after characters typing in remote terminal is very slow)

I checked it using Asterisk echo test.

Please advice