Hosts and Links are 2 different subjects.
Hosts are servers, from the TT explanation is that if your remote server goes down for whichever reason, then it will failover and try to connect to the 2nd one configured in TT Guardian. in the case you going tru the same link still.
In the case of a complete different link. [ cable, dsl,... ], the problem is that Guardian is trying to get somewhere from a Link. if that link goes down, then i tgets puzzled a bit... since the routing changed.
Since you log in from an IP X, when you switch connection with IP Y, the remote server doesn't know that you are the same person. So your login from IP X will timeout.
So technically, you have no choice unfortunately to login again, and usually Guardian gets confused and i would suggest [ because it is a quicker and safer fix ] to simply restart Guardian then log back in and hope you didn't lose too much time and that you didn't have a position...
hope this make sense. ;p