This is my topology:
Call between IP Phone and IP Phone is very well but from IP Phone and PSTN through R2811 is intermittent.
When i ping from router 2811 to ip phones, i get 5 success and 1 fail.
All port on CE500 are configured as IP Phone+Deskop 100/full. giga ports connected to Cat3750 are switch ports 1000/full with native vlan data vlan.
I don't what is the reason of this issue.