Net lag is the phenomenon of plane position distortion resulting from non-instantaneous communication between all the computers running Warbirds. Translated into english, Net Lag is the inaccuracies of what you see on the screen vs. what the other guy sees due to communication delays across the internet.
It is *vital* to understand Net Lag to avoid frustration and to fight effectively in Warbirds. First I will describe my understanding of how the FE (Front End) to Host communication system works.. Once this is done, I will discuss the various situations in Warbirds, and how Net Lag alters reality.
Warbirds is a unique game, in that unlike regular games where all the action occurs in one spot (on your computer), Warbirds occurs on hundreds of computers across the world. Every player has a copy of the Front End, and all communicate with the Host. The Front End consists of the flight simulator and the gunnery system. All flying and shooting (including collision detection, plane flying characteristics, and gun hit determination) occurs on the Front End. Thus, the only computer that determines whether you hit another plane is your own, the only computer that tells what your plane does is your own, and the only computer that determines whether you hit someone/something with guns or ground ordnance is your own. No collision detection or ordnance hit determination for you or anything you drop/fire is done on any other computer including the host.
The host is Grand Central Station for Warbirds Information Exchange. Front Ends send messages to the Host, and the Host processes these and dispatches messages back to the Front Ends. The information that the Front End sends to the host are system commands (including plane selection, ordnance selection, base selection, and other commands such as ".fly), messages to other FE's (messages you type, including voice communication), positional information (what your plane is doing and where it is), and ordnance damage information (what you hit, how many rounds fired). The host receives all this and processes it. It sends out to the Front Ends positional information for other Front End planes, damage reports to the Front Ends (which includes FE's plane damage, other plane damage, and ground target damage information), Messages (those that others type to you as well as system messages, including kill messages), and System Commands (such as "your dead", or other system commands, including ejection and other administration commands).
It is vital to understand how the system works in order to understand net lag. The host has no idea of the terrain (except for damagable object information, and the status of the bases and task forces), nor does it do gunnery hit determination or collision detection.
So how does net lag fit into all this? All this message exchange and processing takes time. In order for a gun hit to register on the target's computer, the hit message has to be sent to the Host (anywhere from 1/8th to 1/4th of a second), processed by the Host (anywhere from 1/4th to 1/2 a second, depending on how busy it is), then sent to the target's FE (anywhere from 1/8th to 1/4th of a second). Thus a hit can take up to 1-2 seconds to register, assuming no other (net) delays in communication. Damage to the target gets bounced back to the shooter from the host (not from the other guy's FE), so that the shooter's FE can shows parts falling off and other effects. Positional Data is done the same way, each FE sends positional data for it's plane approximately two times a second to the host. This information is processed, collated, and sent to all the appropriate FEs. This can take a second or two. Here is where the delay occurs. It is vital to remember that any other plane you see in the air is actually their position 1-2 seconds ago on their FE, not their position on their FE at that instant. Thus their actual position could be 1-2 seconds "further along" in reality, on their FE. In addition, your position on their FE is 1-2 seconds old, thus is 1-2 seconds "further behind" in reality.
Always keep in mind: What you see of the enemy is where he was and what he was doing 1-2 seconds ago (on his FE, he has flown for another 1-2 seconds). What he sees is what you were doing and where you were 1-2 seconds ago (you have flown for another 1-2 seconds, but his FE doesn't have that 1-2 seconds of positional info yet). In addition, any reaction you have to something he is doing gets seen in 2-4 seconds after he did whatever you were reacting to. For example, you see him rolling 180 degrees, so you counter that roll. He sees you counter that move 2-4 seconds *after* he did that move. If that move gave him a shot in less than that time, he may have bullets hitting your plane before his FE sees your countermove (which might be bad for your health :) Or, you hear a ping. By the time his FE sees your knee-jerk jink, he could have been firing at you for 2-4 seconds.
Now I will discuss the usual situations that arise, and Net Lag's influence on them:
Headons
Headons are really nasty, because both fighters have a good shot (nether target is dodging), and because both fighters are heading towards each other at a pretty quick pace. Ifboth planes are going 200mph, the closure is 400mph. If both planes are going 400mph, the closure is a whopping 800mph! Thus the planes will go from range 10 to range 2 very quickly. Let's assume that each plane is going 250mph (probably a good average). This results in a closure of 500mph, or a closure of 250 yards per second. Thus each second, the range counter decreases by about 3 (range will go from 10 to 2 in about 2 seconds). How does net lag fit into all this?
Due to net lag, you see your target at his position 1-2 seconds ago. Thus at 250mph he is about 120 yards further forward on his FE. On the other hand, he sees your position 1-2 seconds ago, and at 250mph, you are about 120 yards further foreward than he sees you. This works out so that the range each side sees is the same, a rare case in Warbirds due to Net lag. Unfortunately net lag still has a very nasty effect on headons. Most planes can safely dodge a 500mph closure Headon at range 2-4, if they pull up at maximum G's. When will you see him pull up if he pulls up on his FE at range 3? Remember that the range on both FE's is the same (the net lag effects on perceived position cancel out). It takes 1-2 seconds for his pull-up to be seen on your FE. The distance is being decrease by range 3 every second. Thus he will appear to travel in a straight line for 1-2 seconds longer after pulling up on his FE.. But at range 3, one two to seconds will result in him appearing to pull up range 3-6 further along than he really did. If he pulled up at range 3, this will result in him appearing to pull up on your FE at range 0 to 3 *behind* you! Thus, he will appear to barrel into you without appearint to attempt a dodge. This is the cause of so many "intentional ram" complaints. The other guy really did try to dodge you, and cleared you by 50-100 yards, but due to net lag you did not see this manoever until his "image" had flown through you and was behind you. Thus, unless you pull up early enough, you will die, and he will appear to have rammed you.
Another nasty effect is that best firing distance for Headons is range 3-6. At a closure of range 3 per second (250 yards per second, 500mph closure), he will be *past* you when you hear the pings. If you hear the pings earlier, he fired at range 6-10 or more. Keep this in mind next time you headon someone, and you get nailed after the pass.
Tail-chase, no turns
A tail chase situation is where one plane is being followed by another. This often occurs when someone is fleeing from a bad situation and an enemy plane decides to follow. Here is where the greatest difference in perceived range occurs.
Since each FE sees the other FE plane's position 1-2 seconds ago both pilots will see the other plane further behind from where he is. Thus, if you are behind someone, he will appear to be further behind than he really is on his FE. He will appear to be closer to you than if your FE had instantaneous position information on his plane. And you will appear further back to him than you would if his FE had instantaneous positional information. How much closer/farther depends on speed. The faster the planes are going the further the planes travel in that 1-2 seconds. A 500mph plane appears to be 250 yards behind where he really is to the other guy. A 100mph plane, on the other hand, appears to be 50 yards behind where he really is to the other guy. If you are being chased by another plane, that plane's real position is 1-2 seconds further forward than he appears.
How does this all work out? Say you are being chased by someone, and he is at range 7 behind you (from your perspective). Say you both are going 500mph (you both just finished a long dive). Assume net lag is 1 second in this case. His position, on his FE, is 1 second further forward than you see him. At 500mph, you travel 250 yards in one second, thus he is really at range 4 on his FE. Now he sees you at your position 1 second ago, thus he sees you 250 yards behind where you really are. He sees you at range 1, and if he has his guns on you, you are going to die a horrible death, wondering how the heck he made that range 7 shot! (when in fact on his FE it was an easy range 1 shot).
This disparity in distance increases with speed. Thus the faster you both are going, the further the disparity. At 500mph, 1 second delay, if you are chasing someone he sees you at range 5-6 further back than you see him. On the other hand, if you both are going 100mph, a 1 second delay results in him only seeing you range 1 behind where you see him.
This gets nasty when you accelerate. Assuming you both accelerate at the same rate (and thus your "real" range doesn't change), the disparity in range increases. Thus the guy who is behind will appear to close with the guy in front from his FE, while the guy in front will see the guy behind appear to fall away. Just the opposite occurs when both slow down. The guy in behind will appear to see the guy in front pull away, while the guy in front will see the guy behind close the distance.
Turns
Turns are nasty as well. Due to net lag, you see the other guy where he was 1-2 seconds ago. Now if he is on your 6, you see him 1-2 seconds earlier in the turn. Thus he might not appear have his guns on you at all from your FE, yet from his FE, he has already pulled lead and is ready to shoot. In real life, you are safe in a turn fight as long as the barrels of the enemy are pointed right at you (and he thus isn't pulling lead). In Warbirds, you are most likely taking fire if you see the barrels pointed at you, and are in danger of being shot if his nose is within 20-30 degrees of being pointed at you, depending on net lag times. Since you see his position 1-2 seconds ago, and he sees your countermove 1-2 seconds ago, any last-second jink to avoid fire from your FE will be seen 2-4 seconds later on his FE from when he does whatever caused you to jink. That might give him enough time to put enough lead in you to make you blow up. Always start jinks 2-4 seconds before it appears you need to.
Collisions
Because of net lag and the way the system works, no two FE's see two plane's position in the same place. You can guarantee, unless the other guy is totally still (and so are you) that where he is on his FE is different from where you see him, and vice versa. Thus, if you fly into the other guy so that your FE sees both planes in the same place (collision), the other guys FE might not see this. In fact, the other guy's FE might never see your plane get anywhere near his plane. This is why decisions on collision are made by the FE. If your FE sees a collision, you die. If his FE sees a collision he dies. Your FE seeing a collision does not affect whether the other guy dies and vice versa. *His* FE must see the collision for him to die, and *your * FE must see the collision for you to die. The reason that the system does not kill both if one FE detects the collision is that there is no way to predict what the other guys' FE sees. If it were set up so that both planes were killed if one FE saw a collision, you could die from a collision you never saw. For example, take the classic headon situation. You pull up at range 5, just to be safe. You pull up so hard, you don't come within 200 yards of the other guy from your FE. Remember that 200 yards is two football fields in distance. He barrels right in on his FE into your image (which due to net lag is still headed right to him), without ever jinking. His FE detects a collision. Therefore he dies. With a both-die rule, you would also die, even though you did everything in your power to avoid the collision and didn't come anywhere near his plane on your FE. This is why both planes do not die, as it is simply unfair (and would give dweebs an easy way to ram-kill people, which would make Warbirds no fun to fly *real* quick). The way it is done now (with your FE deciding if you live based on your "perspective" of the world) is a necessary evil of Net Lag, even though in "real life", a collision would most likely destroy both planes.
The responsibility of avoiding collisions rests completely on your shoulders, if you want to live. If the other guy wants to live, he is completely responsible for dodging a collision, not you.
This situation gets nasty in tail-chase situations, since if you run into the other guy, his FE sees you 100-500 yards behind where you see him (depending on speed). You don't even come *close* to him, let alone occupy the same space, on his FE. This is why when one plane rear-ends the other, the guy behind always dies, and the guy in front *never* dies (at least not due to the collision). In order for you to get his FE to collide, you have to fly in *front* of him, about range 1-2 or more. Now if you are too far foreward, you are all of a sudden present a big fat target for him to shoot. Plus it is very difficult to maintain this position, as you almost always cannot see him (that damned char/pilot armor in the 6 view :). It is virtually impossible to intentionally kill someone by a rear-end collision.
Same thing happens in a deflection shot where the shooter hits the target with his plane (intentionally or not). The Target's FE sees you 2-4 seconds behind where you see him, thus will see the shooter pass safely behind him, and thus no collision. The shooter, however, if he messed up and didn't dodge in time, is dead.
Climbs
There are two types of climbs, zoom climbs and sustained climbs. Sustained climbs work just like a tail-chase situation, the faster you are going the more closer the other guy is on his FE when you are above, and the farther he is on his FE when you are below.
Zoom climbs are another matter. Since you both are losing speed rapidly, the disparity of perceived range between the two planes diminishes. Thus the guy below sees the guy above appear to pull away (assuming both are decelerating at the same rate), and the guy above sees the guy below appear to get closer. This works to the detriment of the guy below because he will probably be denied a shot he would have had had he instantaneous updates on the other guy's position. When the above guy starts coming back then the situation turns into a regular Headon situation.
Dives
Dives are really, really deceptive. Basically, the guy in front will always have an advantage.
When two planes dive, both planes rapidly accelerate. This results in the guy above appearing to gain on the guy below (from his FE), and vice versa. The reason this is nasty is that when a slower diving plane chases a faster one down, he appears to be keeping up when he's actually losing the dive drag race. On the other hand, the guy below sees the guy above appear to pull away, thus gains confidence that he's succeeding when he's diving. Many people are suckered this way into following a guy down even though they don't have a chance of catching their target.
When both bogies level out, speed begins to drop. What this does is cause the guy in front to appear to pull away to the guy behind, and vice versa. If two identical planes perform identical dives, one two seconds behind the other, the guy behind will probably not ever get a decent shot. Very few people can hit a diving plane at ranges greater than two (due to speed-induced nose-up tendancies), thus one usually has to wait until the bottom of the dive to get the shot. But then, just as you line up your range 3 shot, the same-type bogie starts to pull away! (from your FE's perspecitve, due to the slowing down). On the other hand, the guy in front sees the guy behind gain a bit on him, another illusion. Usually this results in a jink, assuming he can see the guy behind him, further making life difficult for the guy behind.
This net lag is why the Dora is such a great escape artist. The Dora isn't significantly faster than several other planes in a dive, in fact if a P51, F4U or Ki84 has extra energy over the Dora before going into the dive, the P51/F4U/Ki84 will actually gain ground on the Dora before the level speed superiority kicks in. Unfortunately, when the Dora and the plane following level out, the rapid slowdown causes the Dora pilot to appear to pull away from the Ki84/P51/F4U pilot's FE, denying him a decent close-range shot. This will happen even if the follower was on the Dora's 6 range 2-3 when starting the dive. By the time the speeds stop slowing down (and the slow-down induced "pull away" stops), the Dora is going faster than the follower, and pulls away by sheer speed advantage. Thus even if the follower is range 2-3 when the manoever starts, he quickly sees the range go to 4-6, then never get closer, even though he might initially have more energy and in "reality" gains ground.
Micro Warps and that "convenient" warp he does just as you begin shooting
To understand why this occurs, and why the target isn't "causing" the warp intentionally, one must understand how planes are shown on your FE. Your FE receives updates on planes nearby (range 20 or less) once every 1/2 second (or longer, depending on a number of factors, including numbers of bogies in the area). The FE simply can't place the plane in one position, then move it when it gets another update, since this would cause a jump, or mini-warp. Thus what it does is receives the position of the plane, it's velocity vector (speed and direction), it's rotational speed (how fast the plane itself is rotating, and which direction), and the plane's acceleration vector (which direction and how fast the plane is accelerating). This information is used to predict the plane's position during the times in between updates, and when a new update is received, the plane is simply moved to the new location and this all repeats. This allows a smoothly manoevering plane to be displayed on another person's FE almost seamlessly, as you can see when a plane does a normal turn, since the plane appears to fly a rough circle instead of bounce around.
Unfortunately, this system cannot predict a sudden manoever that is radically different from what was happening during the last update. Thus if someone suddenly rolls, or reverses a fast roll (with a fast-rolling plane), or suddenly pulls back on the stick (or pushed forwards), then the FE might not see this for up to 1/2 second, and when the update *does* arrive, the plane may appear to "jump" 20-30 yards. This is more than enough to ruin a good gunpass.
Now this almost always occurs when an enemy either spots you closing for a guns pass, or when he gets hit. Say you ping him, as you close on his 6. 1-2 seconds later, he hears that ping and yanks the stick left and back. 1-2 seconds later, you see this move. During this 2-4 seconds, you were adjusting your aim, and squeeze off a burst. Suddenly your FE gets the update, and moves the target 30ft to the left just as the shells are about to hit. Your shot misses, conveniently for the target (though *not* intentionally convenient). A variant on this is you are closing to the kill, he sees you at his range 9 (your range 7), he rolls suddenly (or does something else radical), then 1-2 seconds later, at range 3, you are lined up perfectly, about to fire, then boom! your FE gets an update, and moves his plane 30-40 feet, blowing your high-speed guns pass. Again, not intentional by the target, but an artifact of net lag, the 1-2 updates per second, and the smoothing code between these updates.
Intentional Ramming
As was mentioned in the collision section, each FE determines whether the FE's plane dies. Thus, in order to get another plane to die in a collision, you have to move your image of your plane on his FE into him. This means predicting where your plane is on his FE down to the foot, as well as his position on his FE. Simply running into him (other than headon) isn't enough, due to net lag, as you will pass by harmlessly on his FE and he will live while you die.
As far as predicting your position on his FE (and his), you have to know 2 critical things: the net delay from your FE to his, and vice versa (they may not be the same). Since this is virtually impossible to determine, you can never be quite certain where you are, or where he is on his FE. You need to know both in order to vector a collision, as well as know both's exact speed.
Thus it is exceedingly difficult to kill someone *else* in a collision between your plane and his. On the other hand, it is painlessly easy to do the reverse, simply run into someone from behind, and blammo, you die (and he almost always lives).
Warp on Demand
This is also yet another difficult stunt. Warp On Demand is only useful if you can "disappear" for a few seconds, then reappear in a more advantageous position (including escapes). Unfortunately, if the host is not receiving updates on your position from you (necessary in order to cause your image to warp on someone's FE), you are not receiving your target's position either (thus have no idea where he will be when you appear again, he might appear on your 6).
Now things get even more complicated. If your connect goes to pot, you cannot predict what your plane was doing last on his FE. Your plane could be flying in a straight line, making a very easy target, for all you know. It may have been slowing down, making for a nice low-speed-target gun pass. You can never be certain, and the average is split down the middle (a warp will either hinder the other guy, or help him kill you). Plus there is the risk of never reconnecting at all (giving him the kill anyway if you were pinged at least once before warping). Basically, the risks of Warp On Demand are great, while the benefits are not guaranteed. Thus there is little to no incentive for Warp On Demand, and trust me, without any benefit, most people won't do it (except for the occasional thrill). Thus most apparant lucky warps are almost always due to factors other than an intentionally-induced warp.