ISO/IEC 29341-15-10:2011(E) Describes the Content Synchronization service which enables two or more ContentDirectory services [CDS] to synchronize content with each other. This service also enables a UPnP control point to synchronize content with a ContentDirectory service. We refer this service as "CSS" or "ContentSync service" from hereon. If a CDS wants to support synchronization of objects and its resources with other CDSs, the implementation MUST enable this ContentSync service (CSS). CSS keeps change log as part of CDS object property that describe which CDS objects are added or modified or deleted since it has synchronized last. Since synchronization enables interaction between ContentSync services, each service has a Control Point (CP) functionality that invokes actions to other ContentSync service to achieve synchronization of contents with each other. This service definition is compliant with the UPnP Device Architecture version 1.0.