Step 1: UserA makes call to the number assigned to UserB

Step2: Call reaches OCS Front End server

Step3: OCS Front End Server does Reverse Name Lookup and Find out SIP URI of UserB

Step4: OCS Front End server finds the active end point of UserB

Step5: OCS Front End Server forks the call to all active end points where UserB has logged in.

Step6: UserB doesn't pick up the call

Step7: OCS Front End server finds out if UserB is enabled for Unified Messaging.

Step7: OCS Server will determine dial plan of the user and query Dial Plan to know the list of UM Servers

Step8: It will select the UM Server based on routing logic and OCS Server will forward the call to Voice Mail.

Note: If first UM Server is not available then OCS will select the other UM Server attached to the same dial plan.

Step 9: Now Session is established with UM Server

Step 10: UM Server will exchange Media packets with UserA directly.