Use of Sendto and WSASendTo by Multicast Senders

Senders that join multicast sessions using the WSAJoinLeaf function are required to call the sendto or WSASendTo function with the correct multicast session address to send data to the multicast session (even though the multicast session address is already provided with the WSAJoinLeaf function call). If the sending application calls the sendto or WSASendTo function specifying a multicast session address other than the address specified with the WSAJoinLeaf function call, the data will not receive QOS provisioning. This requirement is due to the fact that the sender's RSVP service generates the RSVP session based on the multicast session address specified in the call to the WSAJoinLeaf function.

Also note that QOS-enabled applications should only call the sendto or WSASendTo function when acting as a multicast sender. Unicast (UDP or TCP) sender applications must specify their destination address using WSAConnect, and it is sufficient for that application to use the send or WSASend function calls, rather than the sendto or WSASendTo functions.