何旭:
Are you looking to send udp multicast?
Unfortunately I don't have access to the code anymore, but I've done that a couple of times at my previous company to communicate with some specialized devices on the LAN.
It's the same code you'd use to set up an ordinary UDP socket.
HOWEVER: The main problem is setting membership, which is not supported by usocket. I believe LispWorks does have support for it, but my memory is hazy and my searching isn't returning any results, so I may be mistaken.
Either way, what I resorted to doing (with SBCL) was to get the native socket handle and call setsockop on it myself. Really not recommended, but I saw no other way around it, unfortunately.
I don't know what you'd do with LispWorks other than poke around with double colons to find the native handle.
Once you set the membership you can call usocket:socket-receive and be on your merry way.
Now, if you're interested in broadcast that's a different issue, and those are supported by usocket and LispWorks directly.
Hopefully this is more helpful than harmful, since I don't condone accessing private package symbols, much less those representing non-lisp objects