At any one time I have about 1 - 4 users logged on to their office network (via 3900 VPN) using Mac OSX connecting via L2TP.

Every user gets disconnected after approximately 1h48m... and by approximately I mean 1h47m57s or 1h48m5s but always around 1h48m

I cannot find anywhere where this is a restriction or time limit! Any ideas?