The MPLS WG Archive

[Loa Andersson <loa@pi.se>]

All,

if the authors agree that Ina is right, and I think she is (at least
in essence) there is more to be desired in the definition of
soft/hard preemption.

my take is that (note this is not a defininition) hard preemption is
when you remove LSP(s) in order to make place for more important one(s).

Soft preemption is when you use the possibility to (temporary) overbook
a link, counting e.g. diff-serv to throw away less (or none at all)
traffic on the LSP with the lower priority than would have been the
case doing hard preemption. And then try to re-route part of the LSPs
on the link where the protected LSP(s) has placed.

I guess that soft preemption is this two step activity, first move
then re-route to get rid of an unacceptable overbooking situation.

An interesting question is whether it is hard or soft preemption

I suggest that a clear definiton on soft preemtion meeds to go into
the document, and that the diferences with hard preemtion is spelled
out.

/Loa



Quoting Ina Minei <ina@juniper.net>:

< snip>

> 	I think I see you point now. Let me rephrase it, to double
> check my understanding. The idea is to do hard preemption
> anyway, if the over-booking resulting from it is not terrible. In the best
> case, we get nice behavior for everyone, in the worst case (head-end
> doesn't support soft preemption) then the timer will take care of it.
> Right?
> 	In that case, maybe the section can be clarified a little. As it
> stands now, it seems that the cause-effect logic is reveresed, at least
> for someone like me who thinks that the default behaviour is to only do
> soft preemption when requested.
>
<snip>

/Loa

Loa Andersson
+46 739 81 21 64