Well, when I started looking at logic usage that started to be the largest factor. If you have 6 players and 100 Actors in total, thats 6 * 100 checks per update. Which is a lot if its dict checking etc.
In terms of creating a new actor, what happens if a client joins after the actor is created? I'm used to just having some check on the other side to see if we have the player registered otherwise we create it. Would you suggest that when the server evaluates the replication for the new client it invokes a create function on the client? I'm not really wanting to add RPC functionality beyond the scope of the actors themselves (using directed methods mentioned before) so I would imagine the client would simply deduce if the actor existed and if not create it. The reason I asked this question was because I originally believed that the WorldInfo class did not derive from Actor and So I wondered what sort of black magic was taking place to match the instance on the server to the instance on the client. I think I shall let that wait for now. (the replication of world info).
Another question about reliability. can I confirm that whenever a reliable packet is attempted to be sent to a peer, it stores it in a reliable buffer, and checks the ACK packets to see if it got there, else it will resend it. If there is not enough bandwidth, it will ramp up the netpriority until it forcibly enters the outgoing queue. How does this deal with out of order delivery? I've yet to notice any signficant packet loss in my experience, so I've never worried considerably about order of packets, but if you resend a packet it then creates an out of order sequence on the receiving end. Should I drop the packet but ACK its receipt?
Also, I updated my post above to reflect my evolving thought processes! I shall quote it here, if you would be as kind as to read it!
I'm also using Unreal's networking model as inspiration for my own project, though I'm using C# for it.
Anyhow, a few points:
Actor checking: I suggest adding actors that could possibly be replicated (that aren't already provided by the level itself) to a separate list to be checked. You would further eliminate unnecessary checks by allowing actors to specify a replication rate so less important actors need not use as many resources.
And yes, if a client joins, the server would evaluate replication for that client and send it any actors that are relevant to it and they have not already been replicated to it.
As for reliability, I am using the Lidgren library for C# and used reliable sequenced delivery so packets always arrive but old packets are dropped in favor of newer ones.
As for Unreal networking attributes, bNetDirty is set whenever a property is set on an object in UnrealScript, it is a helper variable so you can skip replication if its false. bNetOwner is true when the client you're replicating to owns that actor, and bNetInitial is true when it is the first time you're replicating so you can send variables that only need to be sent once.
My current source code is available, it might be of some help or it might confuse you. ReplicaManager handles replicating my actors through the IReplica interface. And you can look at my MovementBehaviorcomponent to see how player movement is handled. I just copied how Unreal did it in that case.