One of our customers had established recently a direct SIP connection between its Lync 2013 environment and Cisco UCS for VoIP call.
The integration itself worked well and Lync clients were able to make outbound calls and receive incoming calls from Cisco and vice versa.
With that said, there was one scenario in which if a Lync client received an incoming call from Cisco, if the Lync user click on the IGNORE option as shown below, the call will result in Fast-Busy signal if the default voice mail system is not Exchange Unified Messaging.
The default behavior for those type of calls it is to go to the destination user Voice Mail, but that only happens if the its voice mail system is Exchange Unified Messaging.
For customers who are not using Exchange Unified Messaging and decided to continue working with their existing Voice Mail System (Unity or Asterisk for instance), the caller will result in having a Fast-Busy signal instead of redirect to the user Voice mail which is not the expected behavior.
MSPL for Help
In order to change that behavior, we’ve developed a MSPL Service script which reside on the Front-End server and listen for any incoming calls which include SIP 603 Decline in the header, which is the result of a user clicking on the IGNORE button.
603 Decline – The callee’s machine was successfully contacted but the user explicitly does not wish to or cannot participate. The response MAY indicate a better time to call in the Retry-After header field. This status response is returned only if the client knows that no other end point will answer the request.
With the help of the MSPL service, we’ve set our script to change any SIP 603 Decline and return 480 Temporary Unavailable instead, meaning that when a Lync user click on the IGNORE option on his side, the Front-End service will return the Cisco GW with a 480 Temporary Unavailable instead of 603 Decline which will result in continuous ringing on the Cisco side which will lead to the Cisco Voice Mail system and the expected behavior by the user.