Lync client call Ignore option result in fast-busy signal for incoming calls coming from Cisco

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.



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  2. Jeff Piper

    Is there perhaps a place I can find this script? Although I am pretty well versed in c# this may be a little out of my league and this looks like the PERFECT solution.

    1. Guy Bachar (Post author)

      Unfortunately, it’s available only for purchasing.
      But if you are good with C# it shouldn’t be difficult for you at all as there are plenty of documentations and examples on the MSDN.
      The basis of it all is to have a services on the FE that listen to every incoming call and base on the header it manipulates the response.


      1. Jeff Piper

        Please sende the purchase details in an email so I can evaluate that as an option.


        1. Guy Bachar (Post author)

          Hey Jeff,
          I’ll need some more information about your environment​ and what is it exactly you would like to achieve​.
          you can send me more info at guyb at

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