Hi Adrian, See below.
> -----Original Message----- > From: Adrian Farrel [mailto:[EMAIL PROTECTED] > Sent: Thursday, July 20, 2006 7:17 AM > To: Igor Bryskin; JP Vasseur; LE ROUX Jean-Louis RD-CORE-LAN > Cc: [EMAIL PROTECTED] > Subject: Re: [Pce] P & I flags > > Hi, > > This thread went suddenly very quiet in response to Igor's > question which is > a shame because it is a good question. > > When you are doing a path computation how do you know why you > can't reach > the destination with sufficient bandwidth and low enough delay? > > Is it because there is not enough bandwidth on the low delay path? > Or is it because there is too much delay on the high bandwidth path? > > The issue becomes unmanageably complex when there are many > constraints, and > is particularly difficult when those are absolute not > relative constraints. > > Of course, it is always possible to make some guesses, but > usually these are > based on varying the constraints to see what could be > achieved. The choice > of which constraints to vary, by how much, and in what order is very > suspect, and (as when we discussed constraint relaxation) > should be the > subject of policy either at the PCC or the PCE. > > For example, a response that says "If you relaxed the > required bandwidth by > 10% you could get a path" is no use to a PCC that MUST have > the bandwidth, > but that would be happy to relax the delay constraint by 90%. It seems that a <Minimum Constraint> option to PCC specified constraints would be one approach to your example (an analogous <Minimum QoS> approach is being used for example in NSIS QoS signaling, see e.g., http://ietf.org/internet-drafts/draft-ietf-nsis-qspec-10.txt). If the PCC gave its <Minimum Constraints> = <90% * Bandwidth, 10% * delay>, that would work in this case. Thanks, Jerry > > Adrian > > > ----- Original Message ----- > From: "Igor Bryskin" <[EMAIL PROTECTED]> > To: "JP Vasseur" <[EMAIL PROTECTED]>; "LE ROUX Jean-Louis > RD-CORE-LAN" > <[EMAIL PROTECTED]> > Cc: <[EMAIL PROTECTED]> > Sent: Monday, July 17, 2006 5:03 PM > Subject: Re: [Pce] P & I flags > > > JP. > > > >>> IB>> This is the whole my point. If there is a set of > >>> mandatory constraints, > >>> there is no way for a PCE to tell because of which particular > >>> constraint(s) > >>> the computation has failed, > >> > >> Why, if it is clever enough to detect a blocking constraint? > >> > > > > I agree with JL here. There *are* many ways to figure out which > > constraints could not be satisfied, in which case indicating this > > information to the PCC is quite useful. > > > > IB>> I am just curious. Could you (or anybody) describe > > just one of the > > ways > > how PCE can figure out which of mandatory constraints > > caused the path > > computation to fail? > > > > Thanks, > > Igor _______________________________________________ Pce mailing list [email protected] https://www1.ietf.org/mailman/listinfo/pce
