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In the Cisco CallManager 4.x environment, the 7920,7940 and 7960 IP Phones unregister frequently and need to be unplugged and plugged again in order to get the IP Address and configurations.
The Application Event Log shows the "Event Id 3 - DeviceTransientConnection - Transient connection attempt" error message
The IP Phones, which are registered to Cisco CallManager 4.x, unregister from the Cisco CallManager and are required to be unplugged and plugged back in to get back the IP Address and its configurations. This issue is observed only on the specific IP Phone models namely 7920, 7940 and 7960. This error message appear in the application event log:
Explanation: A connection is established and immediately dropped before the registration is complete. Incomplete registration possibly indicates that a device is rehoming in the middle of registration. The alarm can also indicate a device misconfiguration, database error, or an illegal/unknown device that tries to attempt a connection.
Recommended Action: No action is required if this event was issued as a result of a normal device rehome.
There are some possible reasons that this problem occurs:
There can be replication issues between Cisco CallManager databases. In order to check this, run the DBLHelper app to check good replication. This is ideally located in c:\program files\cisco\bin\.
If the phones unregister across an Internet connection, this behavior can be expected once in a while. IP telephony design recommends end-to-end QoS configuration, which is something that is out of your control if you use the Internet.
The Spanning Tree Protocol (STP) is not configured on the switch so there are loops.
In order to resolve this issue, try to increase the keepalive timer on the Cisco CallManager in order to rule out a keepalive timeout issue. Go to the ccmadmin web page and under Service > Service Parameters, choose the server(s) that the IP phones are registered with. In Service*, choose Cisco CallManager. Change the value of Station Keep Alive Interval (sec)* to 45.