ok lets do some math here. i'll take one of my game logs and find a section of high game usage: 22 minutes of sdt = 18037 characters recieved (without ansi). i'll hazzard a guess that ansi adds about 25% more characters, so:
18,000 * 1.25 = 22,500 characters in 22 minutes, or 1 kb/min
modems are rated in kilo-bits per second, so doing a little conversion:
1000 bytes/min * 8bits/byte * 1 min / 60 seconds = 133 bps
to give you a general ballpark, a 56kbps modem on average connects at about 32kpbs (56k connections in real life are extremely rare). now, say that half of your dialup connection speed is upload, so 16kpbs up. at 16kbps upload, you could still host a twgs for 120 people doing SDT full time and not use up all your bandwidth.
now - take my cable connection, which has below average uploads of 344kbps.
my internet connection can handle 2500 players running SDT full time. now, there may in fact be other activities in TW that consume more bandwidth than SDT, but SDT doesn't involve ship movement delays, so it's pretty high up on the list of bandwidth usage. ZTM actually takes up a lot of bandwidth as well, but ZTM really hurts you on the CPU usage because calculating all those warp paths ain't easy, especially when 5-10 players are doing it all at once.
which brings me to the real lag source in most TW games. singularity hits it right on the head. lag hits the worst when the server's CPU is pegged. that happens when the server is doing other things besides TW. the real killer on mine is norton antivirus - when it grabs liveupdates or does a virus scan, the cpu tanks and up goes the lag on the TWGS. playing graphical video games like EVE, WOW, or CS:S also nails the CPU.
finally, there is the matter of ping. bad ping times can feel a lot like lag, but there is really nothing that can be done about bad ping. bad ping results when the client is far away from the server. the only way for a sysop to improve your ping is for him to move his server to a commercial server farm that is belly up to fat fiber. bad ping happens when the internet routes your connection through tons of other servers - or worse yet - overloaded servers.
here is the bottom line: for most servers, bandwidth is not the issue (unless the sysop has other bandwidth hogging activities going on like p2p file sharing or hosting other types of games). bad ping can only be fixed with money. if you want to improve your server's performance, manage your CPU usage wisely.
.