It seems to me client-sync problems are at the root of a whole pattern of flaky behavior, especially in missions, but also throughout the game. I would appreciate some kind of developer comment on this somewhere, for example along the lines of that Salabim note on ranges.
As far as I am concerned, the main problem with client-sync issues is that in every possible situation where it arises, the player gets the short end of the stick.
For the worst example of problems caused by this syndrome, consider mob combat and targeting for nanos, a serious concern for NTs, and also a concern for many other professions. For a mob to attack, all that is needed is the server to believe line-of-sight exists within some range limit. For a player to attack, both the client and the server have to believe that the player has LoS and range. The effect of this behavior mismatch is that when client sync is lost, the player continues being hit while the player can no longer initiate new attacks, including new nano program invocations.
Client-sync is for me routinely lost whenever I move more than a room from a hostile mob in a mission. This may be related also to poor mob pathfinding, but it is primarily caused, I believe, that the client totally loses track of the hostile mob position, and for some reason often may never regain it.
So let us say I encounter an unexpected orange enforcer add deep in a mission level. The only thing I can do is flee to the main room, and either leave entirely or fight and zone. So I run a room or two away, with the stupid enforcer *apparently* hung up on a board-room table, stuck in a pond, or bouncing off some wall, and it seems that I am safe. Suddenly I start taking damage. No mob in sight, nothing I can target. This will continue all the way back to the antechamber, until I zone. On *rare* occasions, the mob in question will appear to teleport into the main room or the antechamber. Usually it never does. Until the client sees the mob I cannot fight it, so of course I have to zone, assuming I survived the flight back to the exit.
On return to the level, the mob is of course right there in the main room or antechamber where it *really* was all along, having in fact followed me closely all the way back to the exit. It's just that the client never saw it.
Similar problems occur throughout missions, with mobs teleporting through walls, with apparently distantly rooted melee mobs hitting regardless of our apparent locations, with nano and attack commands aborting due to range or LoS problems despite apparently standing right in front of the mob, etc. etc. etc. ad nauseam ad infinitum.
Why does this stuff happen? Does it have something to do with the TCP vs. UDP choice? I really doubt it. I think it is just network code which attempts at all costs to save bandwidth and reduce server CPU load coupled with game engine logic that always cuts against the player and for mobs.
There are some obvious possible workarounds to this syndrome or complex of apparently related problems:
* Detect loss of client sync from the server (how hard can this be? Just see if both server and client are reasonably close on their idea of the positions of hostile or nearby mobs every 10 seconds or so) and force sync when this happens. Could be hard to code at this late date, but should have been designed in from the beginning. However, maybe it can't be done at this point.
* (slightly different) Have client detect that player has no LoS to mob which has just done conventional attack (melee/projectile) damage. The client can do this easily when it receives a combat/damage update from the server. If there is in fact no player LoS in the client at the moment that the client is told that there was server LoS from the mob, then obviously sync has been lost and the client should send a message saying "I've lost sync, tell me where the mobs and the player are" -- and incidentally suspending combat and mob activity (at least within missions) until sync has been achieved.
* Send mob coordinates on every attack, forcing position sync in the client when the attack lands. Geez, what bandwidth would this incur -- maybe 12 whole bytes every second? Seems pretty easy to do IMO if the above two things turn out to be too hard.
* Enable client-side player LoS for 1 second following every mob attack. Thus regardless of what the client thinks is going on, if a player takes damage, the client will let the player's nano or attack go off against the enemy which caused the damage, trusting the server to stop it if for some reason it shouldn't happen. This would let me root, calm, or combat some random "invisible" or "teleporting" mob such as I described above. Clearly this solution requires some way to distinguish conventional melee, projectile, and nano attacks from DoTs or similar things, but presumably either the protocol already makes this distinction, or else it would be easy to extend the protocol.
Obviously it requires knowledge of the code and the client-server protocol for a mere player like me to make really helpful suggestions. But the kind of problem I describe above can really be incredibly annoying when it happens time after time. It appears that all the logic in the game engine makes decisions against the player and in favor of mobs. This is particularly infuriating, because it seems to me that from the point of view of "fairness" to the player, that when because of poor game design or even just a bad network connection the player's client goes out of sync with the server, the server should give the *player* the benefit of the doubt, not the mob.
-Strycker NT 80
PS:
Before you ask, I have a new 1.9 Mhz machine with 512 MB of RAM, 60 free GB of disk space, a GeForce 3 card, and a cable modem on a relatively uncluttered HFC network segment. I should have no hardware problems at all that would cause me to lose data, and in fact should do pretty well compared to the majority of other players in terms of the big 4 network characteristics of bandwidth, latency, jitter, and packet loss.
Good stuff
