A data structure used to package messages (that include the package type) sent between the media server and its clients.

This class is abstract. It defines the attributes common to packages where the derived class's type needs to be sent as part of the package. The attributes are a UID that identifies the package's concrete class (so that the server can construct objects of the correct type), and a UID that identifies the package type (the category of classes to which the package belongs). The package type is little used in practice. These attributes and the derived class's size are set during construction of the derived class.