last week I had an annoying problem with Exchange, Lync and PSTN, when a user have simultaneous ringing enabled to his/her mobile number and they don’t answer the call, the call get disconnected or get forwarded to the Cell network Voicemail instead of Exchange Voicemail.
taking a look on SIP stack logs on the frontends I noticed the following error “487 Request Terminated”
so why would Lync do that? so I thought, I’ll take a look on the Voice policy and Trunk settings
started with the Trunk settings, I found out that outbound routing failover timer is enabled on the trunk, basically this option give Lync the power to disconnect the call if no Media were established in 10 seconds – it is a cool feature but not for everyone
then I start looking on the voice policies settings, noticed another problem, the “Voicemail escape timer” is disabled on the voice policy.
what is Voicemail escape timer? I’m glad you asked, this feature allows the Lync to route the call to the Exchange Voicemail when the PSTN number you have for simultaneous ringing is switched off, out of network coverage and try to take the call to its voicemail.
so when enabling this escape timer, the call will keep ring on your Lync client then will be routed to the Exchange Voicemail.
- in Trunk settings, make sure to uncheck the “Enable outbound routing failover timer” box
- in voice policy applied to the user, enable the Voicemail escape timer and set the value of the PSTN Voicemail escape timer to a value between 2000 – 8000 (2000 = 2 seconds), for me the magic value was 2500
after waiting for 10 minutes and trying again, the call was forwarded to the Voicemail of Exchange.