How does UPnP works?

Question

I am doing an app which renders a web page in an upnp enabled television set. I have implemented the UPnP with Cling UPnP Now I am not sure how to proceed further. How is the connection between the Television and the device attained? Is it a socket connection? has anybody got any samples or tutorials regarding this topic which help me to implement UPnP streaming.

I have searched on google but it mainly points to existing apps available in google play. Thanks

Answer 1

Ok, so the service descriptor xml (SCPD) contains <actionList> of <action>s with their parameters, which can be in (to the TV) or out (will be in the TV's response to the action). You need to "call" the action, which means that Cling serializes it to SOAP RPC and sends it to the device as HTTP request. In the response, you will get the overall result of the call as with plain HTTP, 200 for OK, 500 for Bad Request, etc. Each code has a specific explanation in context of the particular action call. The response will also hold out parameters as specified in the SCPD.

But this all is not as much of your interest when using an abstraction library like Cling. It will do everything for you. Disclaimer: i am not familiar with Cling, just with enough other UPnP libs to know where to look for things.

As a TV set, the 3 services you mention will be undoubtely AVTransport,ConnectionManager and RenderingControl. So to present a simple example which will actually do something observable on the TV, let's call RenderingControl.SetVolume. The method you need is org.teleal.cling.support.renderingcontrol.callback.SetVolume. I can't help you to the level of knowing where to obtain the Service parameter, but you should be able to figure out.

I am not saying that you don't need to know how UPnP works under the hood. Grabbing the UPnP specs bundle and reading at least the DeviceArchitecture pdf is indispensable. And you will definitely need the specs to understand the more complicated services like AVTransport. Hint: don't care about InstanceID and ConnectionID. It's all 0 unless you connect to a very advanced renderer (which the TVs nowadays are not).