This question is for an indication/hunch. I realize that it may have been discussed before and that there is no good, scientific answer; nevertheless i seek for experienced/qualified opinions, as there are no definite answers to be found. An indication will be valuable as a clue, hence i ask the community to allow a bit of fuzzyness.
Background:
Consider a very-large-area 3D simulation
- with n participants (peers, people behind NAT) distributed over multiple cities.
- where each participant is seen as one "moving object" in the simulation (hence each moving object is owned by a peer).
- where each peer shall see all other moving object correctly (ie. positional updates are needed).
(The entire simulation is larger, so we now focus on one single blob, and consider it to be the entire "world").
Scale:
- World/blob size 10x10 kilometers (almost flat world).
- Object size: Length max 10 meters
(We omit things like occlusion, optmisations, balancing etc. Assume that all there is needs to be seen and updated).
The nature of "moving object":
- it is physically/positionally restless (compare to a boat in big waves).
- it's movement must be sync'ed to all peers (but individual sync does not need to be simultaneus with other syncs).
- if X sees one, but does not own it, it will behave well (deterministically, by X's local physics calculation) for maybe 1 second, but after that it will diverge (due to different frame rates) and needs a positional update (a UDP packet) from it's owner.
From a peers point of view:
- He needs to update n-1 other peers
- He need to receive updates from n-1 other peers
The positional updates are the critical ones, so focus only on those. One update is ca 20-30 doubles, ca. 200 bytes. Consider UDP only.
As i see it, there are two options. The first one is serverless, where everything works solely on peer2peer communication. The second one is having a server (one, for now) in the middle.
1. Serverless, p2p Each peer must talk with many other peers. One problem is that "Nagle'ing" is useless. First reason is that all endpoints are different, Second is that the local data changes from frame to frame, and there is no point in accumulating multiple frames' data, to send in a larger packet, more sparsely. The oldest frames' data would be outdated. An advantage is however not being dependant on a server.
2. Server-supported Each peer sends it's info to a high-performance, high-bandwidth server which is able to better receive and distribute to all peers, at a fast rate. Similarly, any peer would receive all peers' data from one endpoint only, the server.
Naurally, each peer runs a game loop.
Question: Hopefully based on some kind of experience, what would you throw as a maximum functional number of peers for case 1, case 2? Thx.
