RSVP establishes the per-flow state before the packets can flow.
It is just a minor engineering decision to allow optional circuit
switched service over a best-effort-capable network.
1) I wasn't aware that RSVP caused packets to be routed according to
a flow ID contained in the packet rather than the IP address in the packet.
In this thread, as Noel said:
: It's easy to imagine an ATM-like system
: in which circuit ID's are global in scope.
the circuit ID does not neccessarily imply special routing.
However, you should also be aware that RSVP is virtually useless
without QoS routing.