Rego In Multiplayer Gaming
To kick start the month, here is a great read from one of the Administrators ([-STIPE-]Crazy aka Mike) from STIPE Servers.
Hehehe rego 
That one word which means so much, and We’ve been working on it for over 6 years.
Rego is one of the most troublesome and complex issues and is an on-going problem in multiplayer gaming.
Many gaming companies create their own lag compensation algorithms to help battle the ping differences between players which in result affects the rego on the servers. Eg, A player shoots an Enemy before he ducks behind the wall. But the Enemy had already ducked behind the wall before that player shot. The server must decide: Should the enemy be hit or not?
Using as much as data as possible (like pings of both players + data calculated in the past), These calculations can get very complex – example: doesn’t always mean the person with the lowest ping should be allowed the kill)
Anyway, Rego issues therefore are dependent on the current network status for each player and also the available cpu to calculate them.
CPU – If the CPU cannot keep up with the Lag compensation calculations, then rego will have a major affect. In STIPE’s case, we have modified and tweaked our servers to always have these resources available to the game.
Network – This is the biggest cause. You will never see rego issues in a LAN environment (unless it’s a very crappy network 
). Rego could be perfect if ALL the players have the lowest ping possible. Say if 5 people have 10ms ping and 1 person has 250ms ping, this will affect the game play for all the players. It may be better if all players had 60ms ping instead. (Of course it all depends on how smart the lag compensation algorithm is)
Valve have made a very very very complex system – but has a lot of consequences, there are so many times where bullets are not registered because it believes it wouldn’t be fair if it was registered.
COD Engine is slightly more simple We’ve noticed, but because of this there’s little we can do to tweak them. We try to do what I can.
Many UT engines use a very simple system, relying more on the client. The rego is excellent most of the time but people can pull off so many BS shots including a person with 400 ping – making the game unfair.
In summary if the rego is bad, the server is simply doing its job – trying to ignore shots that are unfair. To improve rego, we need to look at the current situation. IS the network ok? IS the CPU ok? Are the players in the server all with a good stable connection? (Low pings, no spikes, no lags no loss, no choke)
Next time you’re having rego issues, take a screenshot of the player list in your server (including their pings) Then try to kick high ping players out or ones that don’t have a decent connection (like 56k modem or 256k slow adsl or just crappy net) See how the server goes then. (Kicking higher ping players may not solve the issue though – in CSS it does a good job but may not for COD)
Source: stipe.com.au