We are experienced a problem with uc-520. Now, we have connected 2 sites to use IP telephony across MPLS, the uc-520 is at site A, and the phone is at site B. The phone has successfully registered to uc-520. But when the phone off-hooked, we hear the busy tone. When we try using sofphone from site, the call can be connected. So we can't make a call from that phone. But when we connected the phone directly to the uc-520's port, it's working normally.
FYI, we use Cisco IP Phone 3911 (SIP) and Cisco Router 1841.
Any one experienced with this issue? Please advice..