[Nel] Suggestion for the NeL network library / architecture

Tue, 12 Dec 2000 11:37:00 +0100

According to MIGUEL ANGEL BLANCH LARDIN:
+> > At first we didn't see the "server to server" sentence.
+> 
+> Ok, I have a dummy question, but when it is better to have multicast 
+> to a server delivering the messages to the rest of servers?
+
+Quite simple: When you need to send the same message to more than one
+server. As soon as you need to send a message to multiple servers,
+you will tie up bandwidth and CPU resending the same message over and over
+to each server.
+
+Consider the following model. Each agent (which represent an object, NPC,
+PC, the door, the lamp, whatever entity in your world) is represented
+typically by an object in a "world service process". Once your world
+becomes large, you need multiple processes. What happens when an agent
+want to "talk" to another agent on a different process. The agent, in an
+ideal (and OO) world, merely talks to an object located in its process
+space, said object being either the recipient agent itself, or merely a
+replica, which will forward the message across the network to the real
+agent.
+
+You don't need multicast for that: its straight 1-to-1.
+
+However, what if the message is "what is your current XYZ". That's a fairly
+frequent question. If you need to query across the network, you'll quickly
+end up loading the net, just to find the value three variables.
+
+That's where PGM/multicast intervenes. In that model, the agent, when he
+changes some of his variables, notifies the replica that "XYZ are now...".
+I spoke about how the world services organise where an agent resides. In
+some models, you have about one, maybe two replicas, which you can notify
+using a standard TCP stream. Or RDP. But, if you want a load-balancing
+system, you quickly end up with a replica of an object in most world
+service processes. It becomes then more efficient to multicast the updates
+as above to all processes, and update them all in one sweep.
+
+> How portable/compatible is mulitcast technology?
+
+Multicast is working, right now. However, to work across separate networks,
+it requires specific support from IP routers, and resources, which most
+providers aren't willing to dedicate (multi-network multicast is mostly
+used for video/audio "broadcasts", video conferencing or shows).
+
+As for PGM, well, the current library has lots of empty directories and
+"TODO" notes in comments, so it's clearly a work in progress :)
+
+-- 
+Vincent Archer                                         Email: archer@nevrax.com
+
+Nevrax France.                              Off on the yellow brick road we go!
+
+