Make required changes to an application to use the new APIs introduced in SDK version 2.1 ESD #2. You can migrate client applications built from the previous SDK versions 2.0, 2.0 ESD #1, 2.1, or 2.1 ESD #1.
When an existing client application built from a previous SDK version is integrated with the 2.1 ESD #2 SDK and installed on a device it must be fully functional, with its related server packages deployed prior to performing an upgrade, or deploying a new server package after an upgrade.