We consider the N-user broadcast erasure channel where feedback from the
users is fed back to the transmitter in the form of ACK messages. We provide a
generic outer bound to the capacity of this system and propose a coding
algorithm that achieves this bound for an arbitrary number of users and
symmetric channel conditions, assuming that instantaneous feedback is known to
all users. Removing this assumption results in a rate region which differs from
the outer bound by a factor O(N^2/L), where L is packet length.