I have a VPN connection between the headquarter (there is one Cisco2821-sec/k9) and 3 agency (there is on Cisco 2801-hsec/k9 on each agency)
I have also one UC-560 installed at headquarters with IP-Phone SPA-504G for VoIP call
They are plan to install many IP-Phone SPA-502G on each agency and make call with headquarter
Is it possible for users (12) in the Agency to make calls with other user in the same agency if the link with the the headquarter goes down ?
What do I need to perform it.