In message <5512B961-3280-4EBD-8A0B-275AD43358DE@xxxxxxxxx> Fred Baker writes: > > On Nov 16, 2006, at 4:02 PM, Curtis Villamizar wrote: > > Preemption in MPLS can be soft preemption (setting aside > > differences of opinion about how signaling of soft preempt should > > be done for the moment)... > > > > Even for hard preemption, there is at worst a fall back to IP and > > reroute... > > Those are both options, but IMHO have issues. One can't, for example, > fall back and reroute to a different path if the bottleneck where > preemption is occurring is the only path to the destination. [...] One vendor, lets call them vendor A, has solved this using a feature they call metric-bias which is a better alternative to soft preemption. MPLS CSPF is influenced so that an effort is made to avoid highly utilized links. If there is no other way, thats where it goes. If there is other traffic (BE) thats what gets clobberred. But we're way off topic so I won't go into details. > [big snip] > > Yes, I'm being extreme, but this topic is about the end cases. And > yes, adding more bandwidth is always helpful. It isn't always an > option, and under the scenarios in question (in some cases, just say > "Armageddon") might be pretty difficult to predict in detail. Plain IP solutions based on queueing alone work fine if allowing the ETS traffic to take the shortest IGP path never congests the ETS traffic and never gets too painful for the BE traffic. Generally MPLS shines relative to plain IP where there is a network fault, or many network faults, and capacity remains but may be quite limited in part of the topology. That would be expected to be the case in certain situation where an ETS is most needed. For example, multiple faults occurred and capacity was very substantially reduced during and for quite a while after Katrina. Some automatic means of best using whatever capacity is available at any give time (such as MPLS does) would be a good thing IMHO. Do you disagree? Curtis _______________________________________________ Ietf@xxxxxxxx https://www1.ietf.org/mailman/listinfo/ietf