Multicast time synchronization is the Johnson Controls implementation of SNTP w32time with Multicast capabilities and RFC-2030 compliance. Multicast is the most commonly used time synchronization option for Metasys sites. This method delivers the same features as the Windows method, but also provides improved Metasys time synchronization between the Site Director and supervisory devices. A time server provides the time to the Site Director, and the Site Director in turn multicasts the time to all supervisory devices on the Metasys network. By default, the server's operating system synchronizes with the external time server once every seven days.
Multicast time synchronization requires that all Ethernet routers on the site support Multicast routing (Internet Group Multicast Protocol [IGMP]) because the Multicast time message crosses routers. To implement Multicast synchronization across routers, you may require assistance from the customer's IT department.