Firmware update using S_SPECIAL_DATA_SRV will be performed in the following situations:
1. After reboot
Remark: Firmware file will be downloaded if number of attempts of downloading this particular URL is less than a fixed value (currently 1, it can be changed if you want). Number of attempts is only checked in firmware update after reboot. Max allowed number of attempts cannot be changed via provisioning, it is hardcoded in the source code (it can be available for provisioning if you want). This condition is defined and implemented to avoid firmware update => reboot => firmware update loop if firmware file is corrupted. Number of attempts is set back to 0 when S_SPECIAL_DATA_SRV is changed. Number of attempts is incremented each time device tries to download firmware after reboot.
2. After timer
Remark: Timer (in minutes) is defined in BS_IP_Data1.uiI_CHECK_FOR_UPDATES_TIMER_INIT.
3. After check-sync
Remark: Device will try to do firmware update after downloading config file.
4. Manually from WebUI or from registered HS
Remark: S_SPECIAL_DATA_SRV has higher priority so if it is not empty then S_DATA_SERVER and S_USER_FIRMWARE_URL will be ignored.

Example:

<S_SPECIAL_DATA_SRV class="string" value='"http://profile.gigaset.net/42/merkur207_42.bin"'/>

Important is to use the naming like described in the example: "merkur"softwareversion"_42.bin"