SRST Manager - SIP Phones do not Register to SRST Router

https://www.cisco.com/c/en/us/support/docs/unified-communications/unified-survivable-remote-site-telephony/201114-SIP-Phones-do-not-Register-to-SRST-route.html

Cisco IP Phones disconnect causes

Here is a List of the reason codes for LastOutOfServiceInformation

ReasonForOutOfService=10    --  TCPtimedOut - The TCP connection to the Cisco Unified Communication Manager experienced a timeout error

ReasonForOutOfService=12    --  TCPucmResetConnection - The Cisco Unified Communication Manager reset the TCP connection

ReasonForOutOfService=13    --  TCPucmAbortedConnection - The Cisco Unified Communication Manager aborted the TCP connection

ReasonForOutOfService=14    --  TCPucmClosedConnection - The Cisco Unified Communication Manager closed the TCP connection

ReasonForOutOfService=15    --  SCCPKeepAliveFailure - The device closed the connection due to a SCCP KeepAlive failure

ReasonForOutOfService=16    --  TCPdeviceLostIPAddress - The connection closed due to the IP address being lost.  This may be due to the DHCP Lease expiring or the detection of IP address duplication. 

                                                           Check that the DHCP Server is online and that no duplication has been reported by the DHCP Server

ReasonForOutOfService=17    --  TCPDeviceRegsistrationTimedOut - The device closed the TCP connection due to a registration timeout

ReasonForOutOfService=18    --  TCPclosedConnectHighPriorityUcm - The device closed the TCP connection in order to reconnect to a higher priority Cisco Unified CM

ReasonForOutOfService=20    --  TCPclosedUserInitiatedReset - The device closed the TCP connection due to a user initiated reset

ReasonForOutOfService=22   --  TCPclosedUcmInitiatedReset - The device closed the TCP connection due to a reset command from the Cisco Unified CM

ReasonForOutOfService=23    --  TCPclosedUcmInitiatedRestart - The device closed the TCP connection due to a restart command from the Cisco Unified CM

ReasonForOutOfService=24    --  TCPClosedRegistrationReject - The device closed the TCP connection due to receiving a registration rejection from the Cisco Unified CM

ReasonForOutOfService=25    --  RegistrationSuccessful - The device has initialized and is unaware of any previous connection to the Cisco Unified CM

ReasonForOutOfService=26   --  TCPclosedVlanChange - The device closed the TCP connection due to reconfiguration of IP on a new Voice VLAN

ReasonForOutOfService=27   --  TCPclosedPowerSavePlus - The device closed the TCP connection in order to enter Power Save Plus mode

ReasonForOutOfService=100    --  ConfigVersionMismatch - The device detected a version stamp mismatch during registration Cisco Unified CM

ReasonForOutOfService=104   --  TCPclosedApplyConfig - The device closed the TCP connection to restart triggered internally by the device to apply the configuration changes

ReasonForOutOfService=105    --  TCPclosedDeviceRestart - The device closed the TCP connection due to a restart triggered internally by the device because device failed to download the configuration or dial plan file

ReasonForOutOfService=106    --  TCPsecureConnectionFailed - The device failed to setup a secure TCP connection with Cisco Unified CM

ReasonForOutOfService=107    --  TCPclosedDeviceReset - The device closed the TCP connection to set the inactive partition as active partition, then reset, and come up from the new active partition

ReasonForOutOfService=108    --  VpnConnectionLost - The device could not register to Unified CM because VPN connectivity was lost

ReasonForOutOfService=200   --  ClientApplicationClosed - The device was unregistered because the client application was closed

ReasonForOutOfService=201   --  OsInStandbyMode - The device was unregistered because the OS was put in standby mode

ReasonForOutOfService=202   --  OsInHibernateMode - The device was unregistered because the OS was put in hibernate mode

ReasonForOutOfService=203   --  OsInShutdownMode - The device was unregistered because the OS was shut down

ReasonForOutOfService=204   --  ClientApplicationAbort - The device was unregistered because the client application crashed

ReasonForOutOfService=205   --  DeviceUnregNoCleanupTime - The device was unregistered in the previous session because the system did not allow sufficient time for cleanup

ReasonForOutOfService=206   --  DeviceUnregOnSwitchingToDeskphone - The device was unregistered because the client requested to switch from softphone to deskphone control

ReasonForOutOfService=207   --  DeviceUnregOnSwitchingToSoftphone - The device is being registered because the client requested to switch from deskphone control to softphone

ReasonForOutOfService=208   --  DeviceUnregOnNetworkChanged - The device is being unregistered because the client detected a change of network

ReasonForOutOfService=209   --  DeviceUnregExceededRegCount - The device is being unregistered because the device has exceeded the maximum number of concurrent registrations

ReasonForOutOfService=210   --  DeviceUnregExceededLoginCount - The device is being unregistered because the client has exceeded the maximum number of concurrent logons