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On receiving the information that an event has occurred, the LE checks active Links of all active
Application and Scene objects to determine whether some Link must be fired or not. When a Link is fired,
the LE uses the primitive Process-Action() to inform the OP which Action object should be processed.
3. Overview of DSM-CC
The DSM-CC is a set of protocol specifications for managing and controlling MPEG-1 and MPEG-2 bit
streams. These protocols are intended for general applications, MHEG applications, and scripting
language application to setup or teardown a network connection using User-Network (U-N) primitives and
for communication between a client and a server across a network using User-User (U-U) primitives. U-N
primitives are defined as a series of messages to be exchanged among the client, network and server. U-U
primitives may use a Remote Procedure Call (RPC) protocol and may involve U-N messaging. DSM-CC
may be carried as a stream within an MPEG 1 System Stream, an MPEG 2 Transport Stream, or an
MPEG 2 Program Stream. Alternatively, DSM-CC may be carried over other delivery mechanisms, such
as TCP or UDP.
4. Overview of DAVIC
The DAVIC is a consortium whose purpose is to favor and nurture emerging audio-visual standards and
services. These goals are achieved open international collaboration of all members of the DAVIC
consortium. As of today, there are more than 200 companies from 20 different countries who participate
in DAVIC activities. The DAVIC specification is intended to be open and to specify tools, protocols for
handling information flows and not systems. Thus different vendors can make their systems interoperable
if they conform to the DAVIC specification. DAVIC specifies minimum requirements only and it is up to
the vendor to add more functionality.
4.1 DAVIC Architecture
The DAVIC system specification is aimed at providing interoperability. It is based on an abstract
reference model and is made up of 5 subsystems (see [Fig. 2]). A11, A10, A9 and A1 denote reference
points within the system and indicate the information flow between modules. A reference point comprises
of one or more logical information-transfer interface and one or more physical information transfer
interface. DAVIC 1.0 system typically addresses the service provider system (SPS), service consumer
system (SCS) and the delivery between the two. The DAVIC system uses a four-layer service model,
namely, principle service model(SL1), application service layer (SL1), session and transport service layer
(SL2) and network service layer (SL3).