View source for DSM-CC Object Carousel Protocol

[[Image:OC-ProtoLayers.png|right]] 
The [[DSM-CC|DSM-CC standard/toolkit]], which is Part 6 of the [[MPEG-2 Standard]], defines or extends five distinct protocols to cover the many different aspects of broadband service delivery. One of those five includes the "Download" Protocol, which itself contains several variations that detail the transfer of content from a server to a client, either within the [[MPEG-2 Transport Stream|MPEG-2 TS]] or independently in a separate channel.  One of these "Download" protocol variations is an autonomous "data carousel", and an extension to the data carousel itself is the "object carousel".

Stated another way, the '''DSM-CC Object Carousel Protocol''' is a broadcast protocol on top of MPEG-2. It is used for transmission of filesystem hierarchies over a MPEG-2 channel.  Like other protocols (NFS, SAMBA etc. via IP), the Object Carousel protocol allows mounting of external filesystems that are broadcast within a MPEG-2 program.  Of particular interest is its use for the application of interactive multimedia formats, such as [[MHP]] or [[MHEG-5]], for [[Digital TV]] services. 

== '''A.''' MPEG-2 Transport Stream ==

Basically, to mount an Object Carousel, of course you have to know where to find it.

[[Image:OC-LayerMPEG.png]]

First, given a stream location on dvb://ONID.TSID.SID, you have to tune to the service and check some (P)SI tables
for presence of an Object Carousel there (which tables is the subject of the next layers).

As you can see, an Object Carousel '''can''' be distributed over multiple PIDs (i.e. all elemantary streams belong to
the same '''CarouselID'''), and there is nothing more special to say about the MPEG-2 layer of the Object Carousel protocol.
TS-Packets are merged into Sections as usual, and DSMCC-Sections also follow the usual '''PrivateSection''' format.

== '''B.''' Data Carousel ==

[[Image:OC-LayerDC.png|right]]

The '''PMT''' points to elementary streams with '''StreamType 0xb''', on which DSM-CC streams are located, but that does not mean a DataCarousel is really there. You can find various descriptors in the '''2nd ES-loop''' of the PMT which indicate the presence of a DataCarousel, e.g. the '''DataBroadcastDescriptor''' and '''CarouselIDDescriptor'''. The latter one associates a DataCarousel with a '''CarouselID''', so that an Object Carousel can include multiple DataCarousels, each one located on a separate elementary stream.

Well then, you already know all elementary streams including a DataCarousel, but what pieces of data are broadcast there and how to filter them?

A DataCarousel includes at least one '''Download Control Message''' which is repeated more frequently than the broadcast data.
This message is called '''DII''' ('''D'''ownload'''I'''nfo'''I'''ndication) and describes a set of data belonging to the broadcast DataCarousel.


== '''C.''' Object Carousel ==

WIP


==External Links==
* [[Wikipedia:DSM CC|Wikipedia's DSM-CC article]]
* [http://www.interactivetvweb.org/tutorial/dtv-intro/dsm-cc/index.shtml An article covering the IDTV aspects of DSM-CC]

[[Category:Technology]]