I''ve just started directplay programming a few days ago and I have a few questions : 1) How often can I expect multicast abilities on the internet ? For an online game, can I choose an ISP with multicast ? Would such an ISP really allow me to send one to many messages with the bandwidth cost of one message ? 2) How can UDP do "one to many" connections while TCP can only do "one to one" ? (unexplained quote from a Gamasutra article) 3) If no multicast is available, are DirectPlay groups any good whatsoever ? (I fear since DirectPlay has to send each one to many message to every player, it will eat as much bandwidth as if I send each message by hand) 4) Can groups and multicast be simulated ? (Server sends message to one "subserver" client who in turn sends the message to all players in the group.) I know such a scheme would increase lag a lot, but lag is not that important for me since I dont want a fast-action game. Also, would it be a bad thing if that subserver client knew the IPs of other players ? (hacking/cheating)

one to many is just one message sent to many people without any extra coding. It''s the same bandwidth cost.

DPID_ALLPLAYERS is what you use to multicast with DPlay. There are ways to setup groups so that you can multicast to just a select group. Never used it so don''t know. I have my own way of doing groups.

With DPlay (I know 7 is like this, I''m guessing 8 as well), you never handle IPs in source. DPlay assigns a pseudo-random number to each client which you use in place of the DPID_ALLPLAYERS to send to one specific person. You have to devise a way to keep track of those numbers. I use an array. It''s an unsigned Int.

That number is only known by the computers directly connected to that client. In a server/client setup only the server will ever know that number unless you send it to other clients manually.

Clients cannot send each other messages directly in a server/client setup. The security risk only comes in when clients can be hacked to fake messages. It''s up to you to code the server so it can know when a message is bogus (I have many checks in place) and reject it accordingly.

Ben
http://therabbithole.redback.inficad.com

Thanks guys. I''ve had a feeling this was the case, but multicast would have made things _so_ easy, I had to try.