That's a good explanation
@Griffith500.
The league I'm currently running has an average of 11 drivers showing up each week, so far we have used P2P.
Week 1 had no issues.
Week 2 had 2 invisible cars initially but a new room eliminated that issue.
Week 3 had 5 invisible cars initially and a new room didn't make a difference (same 5 drivers affected).
I am considering using Fixed Hosting for the next event, would this sort of connection quality be good enough to host a 10-12 person lobby?
I honestly have no idea what bandwidth is required, because I don't know how much data the game relies on for communicating position, physics inputs, lag-prediction etc. Your ping is also important, but not to your ISP, or some speed test site, rather to the individuals you're playing with.
The easiest way is for you to try it and let us know!
One thing to bear in mind is that the bandwidth for upload in the P2P case scales linearly for all players with the number of players, is constant for a client connected to a fixed host, but scales as to the
square of the number of players for the fixed host itself. So a small change in number of players can have a large effect on required upload bandwidth (e.g. 12 players is 121 lots of car data to send, instead of 225 for 16 players). When you start running out of bandwidth, you get the
effect of increased ping and especially jitter (variance of ping).
The "invisible cars" thing points to some kind of synchronisation between peers in peer-to-peer mode, which may mean that vastly different bandwidth (or, more precisely, latency / lag / ping) connections do not mix well in that mode. NAT type incompatibility also had similar effects in GT5; maybe NAT adds extra latency.
I think what
@Famine found was some reliance on low latency in the P2P case, which complicates things further. Fixed host is more robust for latency; only those with distant connections to the host have problems, everyone else depends on their own connection to the host only.
In GT5, a single distant (high-ping) connection tended to disrupt the whole P2P scheme, somehow, as all players are connected to all others, and everyone is dependent on everyone else's ping (possibly synchronisation, and those mysterious "checks" I suspect exist).
Remember the bandwidth setting ("race quality") in the game sets the frequency of data updates. If synchronisation is an issue, due to latency, then going above a certain frequency (related to round trip speed) might break things for that one player.
EDIT: If everyone is playing on a LAN together, use the fixed host setting. The total bandwidth required is contained on the same bit of ethernet, rather than distributed over lots of hardware in the wider web, and P2P is a monster in that regard. A 16 player game requires 15 times the
total bandwidth in P2P mode than it does in fixed host mode - it is effectively cubic instead of quadratic.
In that regard, anyone who can play online happily in a 10-16 player room in P2P mode can host a minimum of 4 players (including themselves) happily in fixed host mode, at the same quality*. Note that your ping is still important.
* If you can play in a P2P room with n total players happily, then the minimum number of players, including yourself, that you can host in fixed host mode is √(n-1) + 1. E.g. for n = 16 -> √15 + 1 = 4.87... ; for n = 10 -> √9 + 1 = 4. The reduction in total number of connections (e.g. 16 to 5) reduces packet overhead, and you can squeeze a bit more out of your upload.