About Path-Resv vs reciever-sender

["Bouarich, Reda" <Reda.Bouarich@Compaq.com>]

Hi everybody,
Just a quick question to make things clear in my mind. Between a source and
a client communication,  the source (sender) send a Path message to the
client (reciever) after a PDP acceptance then the reciever  responds with a
Resv command.
I did not understand how the sender know that the reciever has requested a
communication the first time since that sender is the first actor of the
communication. I understand that the sender has to send Path message all the
time to overcome the time out mechanism, but the first time, the reciever
needs to contact the source to request something, no?
Any help will be appreciated.
Thanks a lot.
Reda.