The idea of push is UNSOLICITED transfer of messages.
Mail, Pointcast, etc. are _subscription_ messaging services.
We implemented push here, both unicast (LowLat) and
multicast (LSAM). http://www.isi.edu/lowlat and
The primary problem with push
is that it eats bandwidth, and companies seem to
not quite understand that it matters _where_ in
the network system you deploy it.