Sometimes 3rd party SIP app gets  "Warning: 399” from UCM and can not make call.

  Steps:

       1) 3rd party SIP app running on Mobile registers to UCM and can make call on corporate network.

            Register Call-ID: 39QjZG3VVZ

            INVITE Call-ID: 8E~BnPne~7

       2) Switch the wifi network to a non-corporate network on which UCM is not reachable.

       3) Switch the network back to corporate network, the app re-registers successfully

            Register Call-ID: wskCoc1ein

       4) Make an outgoing call, UCM complains "503 Service Unavailable” and Warning 399.

            INVITE Call-ID: 2ensqmQTFl

      Workaround: Admin resets the device from UCM or wait till old existing sip session expires.

     SDL log attached.

Thanks a lot in advance.

William