Most evident are local storage, like VCR-type of devices, and the Internet itself. Local storage devices can be connected through an in-home network to the client presenting the application. Local storage in the sense of the client's local file system or in the sense of cache buffering are not observed in this document. An IP-tunnel refers to a forwarding path which is logically separated from the conventional TV Broadcast transmission protocol but uses the same physical link. Hierarchy in TV Broadcast content TV Broadcast content is modeled in a four-layer hierachy, consisting of service, event, component, and fragment.
Service is at the top, fragment is at the bottom of the hierarchy.
The term service is used to refer to a concatenation of programs, all being broadcast by the same service provider. The programs of a service share some tuning characteristics. The term event is used to refer to a single TV program. An event is a time period within a service and therefore can be characterized with begin and end times. The service provider determines the granularity in which the service is split in events.