Methods, systems, and computer program products for synchronizing data stored at one or more message clients with data stored at a message server where the message clients may receive update notifications and may represent the data using different data structures than the message server uses to represent the same data. In this surface acoustic wave device, the pitches in each of the reflection electrodes vary according to a predetermined variation pattern. The method is used for connecting communication links arranged in a plurality of rings, which traverse a plurality of collocation sites in a metropolitan area. The first selected system is controlled based upon the feed forward control command for the first selected system.