The sender and receiver both would issue a rapi_getfd() call at this point. The call returns an alert socket. The socket is used to send data to the RSVP API. The program should issue a select() call on the socket as a read socket in order to know when asynchronous events are available. The program should not read the socket.
If the program is going to receive data, this is a good point to use select() to wait for path messages that indicate that one or more senders are available. There is an example of this in a later section.
If the program is going to send data, this is a good time to tell the RSVP API that the program will be a sender.