Saturday, 26 November 2011

Analysing DVB MHP application using DSM-CC analyser

I was studying some DVB-T services with DVBStreamExplorer. I noticed that on 546 MHz MUX some services were carrying Multimedia Home Platform (MHP) applications. I decided to study MHP application further with DSM-CC analyser in DVBStreamExplorer. In this exercise I shall only be using DVB Transport Stream Monitor. From that I will acquire both PSI/SI and DSM-CC information.
Image below show stream details for one of the services in MUX, LA7. Besides the common video and audio streams the presence of MHP application can also be seen here. In the stream list references to Application Information Table (AIT) and DSM-CC object carousels can be found. For instance one AIT can be found on PID 0x1ba8 (7080). An DSM-CC Object Carousel can be found on PID 0x1ba9 (7081).

Below can be seen the content of an AIT. That contains various information about the application. That covers such information as application name, transport protocol, initial Java class of application and more.

Next step is to look into the DSM-CC carousel containing the application data. Image below shows that three DSM-CC carousel streams were found. Select the streams so that DVBStreamExplorer DSM-CC analyser will start collecting DSI, DII and DDB sections. These sections will be shown fully decoded on DSM-CC sections tab.

Once all DSI, DII and DDB sections for a carousel have been acquired the data carousels can be decoded. Image below shows raw data of carousel modules found. The object carousel will be decoded from these modules.

Image below shows the decoded object carousel. It shows part of the file directory structure of the application. it also shows the binary content of one of the Java class files that is part of the application.

With DSM-CC analyser in DVBStreamExplorer there is the option to save entire carousel on local file system. After doing so you can then launch your preferred Java decompiler and have closer look at the code behind MHP application. I will leave this as an exercise for the reader.