The following site connection edge is needed by the topology graph:Source site: %1 Destination DSA: %2 Source DSA: %3 Transport: %4

Details
Product: Windows Operating System
Event ID: 1401
Source: Active Directory
Version: 5.0
Symbolic Name: DIRLOG_KCC_CONNECTION_EDGE_NEEDED
Message: The following site connection edge is needed by the topology graph:Source site: %1 Destination DSA: %2 Source DSA: %3 Transport: %4
   
Explanation

This is an Active Directory internal event. Internal events appear in Event Viewer only when the default logging level is changed. Most internal events are for informational purposes only. This event is logged when a site connection edge is needed by the Knowledge Consistency Checker (KCC) to complete the topology graph.

   
User Action

No user action is required.

Related:

The Microsoft Exchange Site Replication Service could not initialize the ESE backup/restore interface. HrESEBackupRestoreRegister returned {error code}. You will not be able to perform online backup and restore of the SRS until the service is restarted.