I have used DPlay in applications with upwards of a couple thousand simaltaneous connections. It can be made to work but you have to play by it''s (unwritten) rules or you will get regret it.

The first is that DPlay must have plenty of cpu. If you don''t give it enough cpu time it will start dropping connections (which increases it''s workload which leads to more dropped connections which increases it''s load further). If you don''t use the thread pool feature you *must* put Sleep''s in your loops to unsure that DPlay threads get enough cpu. Relying on the OS thread schedule is not enough, DPlay demands more.

Practically speaking you pretty much have to use the thread pool feature if you want to scale this high.

DPlay will throttle it''s bandwidth to a given user. This is fine but under load it will throttle it to the point that its pings get through but no data does. This means that you have a "live" connection but it has no useful activity. Meanwhile DPlay keeps allocating resources for all this backed up data until your server falls over.

I eventually gave up fighting and switched to a staight winsock based network layer. It took me about a week to do and stabilty and resource usage improved dramatically.

Ah, thanks Mike. That''s the sort of info I was hoping someone would post. So the bottom line is that DPlay would probably be okay for a small MMOG (<1000 connections?).

Good to know. -Ron

DPlay should at the least be seen as a crutch that gets people who aren''t skilled with coding networking in the door to code on-line games.

It just works. Which is why I liked it a lot when I first used it. There were no surprises when I went from LAN to the net with my DPlay project. Now that I understand networking enough I was able to get the same lack of surprises with Winsock and TCP/IP.

Ben


IcarusIndie.com


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quote:Original post by zfod
I don''t know Ron, but I read what Mike was saying as a clear indication that you would NOT want to use Dplay.

I guess it''s all in how you read it, hehe. It depends, I suppose, on when DPlay started to become problimatic. He said he was running ~2000 connections and having problems. So I just cut his number in half and figured it''d probably run fine at that level Mike, any input on at what point you started to see instability?

I think we can safely say that the 30 person limit is no longer true

It''s not a number of connections thing, it''s what your workload is.

I have seen DPlay work fine, with no special care in how it was used, with 5000 simaltaneous connections to a single server. However there was very light traffic on the connections so the cpu utilization never got above 50%. Also this was on a 100Mb LAN so bandwidth and round-trip-time was at it''s best.

Under heavy load I''ve seen it fall over with as few as 100 connections. This is over the Internet with lots of traffic on each connection. By fall over I mean the cascade failure I mentioned above where DPlay starts dropping connections which causes it to increase it''s own workload for a time which causes it to drop more connections, etc.

IMHO DPlay works fine in situations where it was seemingly originally designed for - small LAN-based games. It can be made to work for other situations but it requires a good bit more babying. If you want a rule of thumb I''d say you need to be willing to commit 50% of your cpu on the server and probably 10%, at a minimum, on the clients to ensure good performance.

If you are already familiar with socket programming and have at least some grasp of what completion ports are then I see no advantage in using DPlay over winsock.