What is the meaning of the "c" flag in DBGSESSID? The documentation (http://www.nusphere.com/kb/technicalfaq/faq_dbg_related.htm?/) does not mention it.

We are integrating DBGSESSID into our project to allow it to be passed through internal socket calls so that we can do "deep debugging". I am just wandering what additional flags are there so we can utilize the debugger to the its maximum.

This flag is set when Tools->Settings->Run & Debug, Debug Session is checked. In this case if you click on a link in the page that was produced under debugger, new page will be started with debugger too. It works with debugger's cookie help. In other words, if you set this flag, debugger will add DBGSESSID cookie to the output, and this cookie sent back to the server upon navigation will trigger debug session.

I'm not sure what you do with your "socket calls" and "deep debugging". If the client of the HTTP request is not web-browser or it is not HTTP request runs php at all, you don't need this flag for sure.

If "deep" side that you're going to debug is running on different server, you may want to check "Use custom host and port" in the debugger settings and have there either localhost (in case of ssh tunelling) or your external IP address (see $_SERVER['REMOTE_ADDRESS']). Otherwise, debugger will hardly find your machine and connect to dbglistener running there.