Are there anyway to detect if a stream is being published?

[xhe]

I am now creating a online video chat apps using FMS 3.5. I now met a
problem, how can I detect if a stream is now just under publishing?
In order to control the bandwidth usage, I decided to allow one user
can only video chat with one other user. But now the difficulty for me
is how to detect the first user is already in video chating when a
third user wants to video chat with him?
My backend server language is PHP, I ever thought of using database to
save if the user is in chat, but that involve a lot extra coding,
sending request from FMS to PHP api, updating DB etc., I hope to use
FMS directly to detect this, just like using File.Exist to detect if a
file exist. such as stream.exist() etc.
Thanks for your reading and waiting for your idea.