I have read DC/OC spec but dont understand very clear.
We have to transfer files to MHP STB, can we use DC?
As I know, DC is not good at tranferring filesystem like files,
so it does not include filesystem structure ,right?
Is this the only reason that we must use OC in MHP?
Thanks in advance!
Well, the main reason why you have to use object carousel rather than data carousel is because that's what the MHP spec says :)
Object caorusel has a number of advantages over data carousel: you've already mentioned the biggest one, which is the ability to represent a filesystem structure rather than just a flat set of modules. The ability to support stream events is also a useful part of object carousel, as is the fact that files in the object carousel are represented as files, rather than as 'modules' which are not really like files. This makes it much easier to support reading from an object carousel in Java, because it maps very easily on to the java.io APIs.
Steve.
In a way, it is. In a data carousel, the data is transmitted as 'modules' that are transmitted repeatedly to make sure that a receiver can load all of the data. For an object carousel (which is based on top of data carousel), a module may contain one or more files.
The DSM-CC data carousel spec gives the option to compress the data in a module before it is transmitted in order to save space. ZIP compression is one of the options that is available - I seem to remember that there are others, but I don't have the DSM-CC spec in front of me to check.
This process is transparent to any higher-level software (e.g. Java) because the decompression is handled transparently by the DSM-CC parser and so the higer level software isn't even aware that the data was originally compressed. It does mean that the people preparing the apps for transmission may need to know about this, however, because compressing files in the object carousel (e.g. using ZIP) may not save any space if the data carousel modules are also being compressed.
Steve.
