Parked calls drop after 30 seconds

Dropped parked calls are due to a RTCP timeout.

Open Lync Powershell to view Trunk configuration

Get-CsTrunkConfiguration

SipResponseCodeTranslationRulesList : {}
Description                         :
ConcentratedTopology                : False
EnableBypass                        : False
EnableMobileTrunkSupport            : False
EnableReferSupport                  : False
EnableSessionTimer                  : True
EnableSignalBoost                   : False
MaxEarlyDialogs                     : 20
RemovePlusFromUri                   : False
RTCPActiveCalls                     : True
RTCPCallsOnHold                     : TrueSRTPMode                            : Optional
EnablePIDFLOSupport                 : False

to resolve the timeout, open Lync Powershell and enter

Set-CsTrunkConfiguration –Identity <TrunkName> –RTCPActiveCalls $false –RTCPCallsOnHold $false

SipResponseCodeTranslationRulesList : {}
Description                         :
ConcentratedTopology                : False
EnableBypass                        : False
EnableMobileTrunkSupport            : False
EnableReferSupport                  : False
EnableSessionTimer                  : True
EnableSignalBoost                   : False
MaxEarlyDialogs                     : 20
RemovePlusFromUri                   : False
RTCPActiveCalls                     : False
RTCPCallsOnHold                     : False
SRTPMode                            : Optional
EnablePIDFLOSupport                 : False

Wait for Topology replication and test call park.