Extended delay between channel creation and ringing

In the past few days, the problem starts to surface.

When a call comes in or goes out, I saw a notice on "New channel", but it will be about 10 seconds later when I can see the "Ring-Ready".

I tried to do traceroute and ping, all seems to be fine, within 50ms.

Would anyone be able to shed some lights on the possible cause please?

Thanks
Jim