30Kb is still a useable amount of bandwidth for a Terminal Server Session, however it is not sufficient for all situations, i.e. if you're using 16/24 bit color, higher resolutions, sound, remote printing & drive redirection the bandwidth required climbs
a bit (usually in about 4Kb increments)
Citrix ICA on the otherhand is a bit less hungry for bandwidth (and can be limited by policy). I monitor ICA bandwidth on my WAN connected sessions and they often stay below 20Kbps, but do spike-up over 100Kbps from time to time.