The so-called
lag-shield is due to a few bugs in Tremulous mods, especially the fact that it treats buildables as Quake3 game entities, which shouldn't be that much of a problem
unless there's lots and lots of them, which is probably something developers didn't predict at that time.
What happens is that, in order to save bandwidth, the server only sends to the client information about what is in view. When a player approaches a
laggy base, the server suddenly starts transmitting a spam-ful of information about the buildables in view, which lags the connection (and results in the perceived
lag-shield). Smart incremental delta-based update techniques could prevent this issue. Second issue: the builables seem to lack LOD (
level of detail) graphics optimization techniques, which makes them quite expensive (slow) to draw. This is the reason why people get 3 FPS in the neighbourhood of a
laggy base -- the computer draws very far away buildables in full detail, which is quite dumb.
I hope this clears up any questions related to
laggy bases in Tremulous.