> From: Caitlin Bestler <caitlinb(_at_)rp(_dot_)asomi(_dot_)net>
> Given the source interface, the *meaning* of an IP header is not
> supposed to be dependent on the routing tables. ..
> By contrast, the meaning of an ATM circuit is dependent on the context
> in which it was established. There is no expectation that there is any
> meaning to this circuit identifier beyond those imparted when the
> circuit was created.
Yes, but that's just a minor engineering decisions, i.e. the use of a
That's the essential requirement for networks capable of best effort
service to let all the packets have globally routable addresses.
non-global namespace for circuit ID's. It's easy to imagine an ATM-like system
in which circuit ID's are global in scope.
RSVP is a case.
The real crucial *architectural* difference is in the fact that there is
per-flow state, along with the need to set up state before the packets can
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.