We have some strange outage in our phone system. We have CUCM 6.1 in the main office with 3 remote sites. These Remote sites are connected via MPLS to the CUCM in the main office. This morning suddenly, the remote locations cannot make outgoing (external) calls. But they can receive and make internal phone calls. They can even make and receive calls from our cluster CUCM in the other city (another CUCM connected via ICT and using the same MPLS)
These Remote sites don't have a direct numbers so all of the incoming calls are routed to the main office and then transferred to the remote location. Incoming seems not to be the problem; the problem was outbound external calls from remote sites.
First, I thought it was PRI/Gateway but the main office has no issue making and receiving external calls. It was kind of strange since the Remote locations outgoing external calls will go to the same PRI/GW as the main office.
I have no idea and the problem was fixed before I was able to debug the gateway. Anyone have any idea where should I start investigating the root cause of the issue? Is it the Telco (PRI), GW, CUCM or MPLS?
Thank you for the input.