The CS Communication Toolkit is aimed at letting developers write third party applications that communicate with CS Extensions. I believe it provides Air and C++ libraries for application developers, as well as an actionscript library for extension developers. I don't believe you can currently use the CS Communication Toolkit to send messages from a native plugin. There are some examples of the CS Communication toolkit in Extension Builder, you can import the samples by going to File > Import and selecting the Extension Builder samples.
PlugPlug only allows communication between a plugin and a CS Extension (or between two plugins I suppose). I don't think there is documentation for PlugPlug - different point product SDKs expose it to different degrees and have different wrapper classes for it. There are lots of examples of using it in the Illustrator SDK, have a look for the *FlashController classes and the SDKPlugPlug class in the SDK.
I don't think InDesign currently exposes it's PlugPlug instance, if you're developing for InDesign and want communication between plugins and extensions then the simplest way is to make your plugin scriptable.
Do you have a particular use case in mind?
Hope that helps,
In my case i want to develop plugin through c++ api but want to design its UI in flex buider or some other tool which make my ui development task easy .earlier I was thinking to develop UI in cs extension builder and plugin in native c++ api and want some communication b/w this two module i.e hybrid extension .can you help in hybrid extension development process for INdesign i.e from where to start and what step to follow.
Is there any solution for my problem other than hybrid extension?
For InDesign the best approach is probably to make your C++ plugin scriptable (see the SDK docs and samples for how to do that), and then communicate through the scripting layer. If you've made your plugin scriptable then you can generate new CSAW libraries using CSAWIDExporter (aka DommyDumper) that let you talk to your plugin directly from Actionscript instead of having to use ExtendScript. CSAWIDExporter and the associated docs ship with Extension Builder 2.0 - in Extension Builder selecting Help > CS Extension Builder Extras should open a folder containing some tools, the CSAWIDExporter zip should contain everything you need to get started.