[e2e] Routing Info - help!

[arjuna at dcs.kcl.ac.uk]

Dear All,

I was going through the paper 'End-to-End Routing Behaviour in the
 Internet' and have some questions:

1)In the Internet,what type of routing occurs at any point of time? i.e
Does the router calculate a shortest single path and routes information
using one single path until there are delays or link failures or does it
calculate multiple paths and send information using the multiple paths at
any point of time?

2)Say if packets P1,P2,P3,P4 are travelling along a single path in the
'backbone' ,are there any instances where P3,P4 could take a different
route suddenly in the 'backbone'?  If yes, which are the instances that
make them take an alternate path. Or is it that the routing changes occur
only in the edges and not the backbone?
3)If a link fails, does packets that were traversing that particular link
get dropped?
I would be very much obliged if someone could help me with these doubts.

Regards,
Arjuna