Correction: RE: [PCN] Architecture draft - probing section & general updates.

["Anna Charny (acharny)" <[e-mail]>]

A typo in my previous message: I meant to say the charter does NOT
restrict the low ingress-egress aggregation.  Edited the appropriate
sentense below...

Anna

> -----Original Message-----
> From: Anna Charny (acharny) 
> Sent: Friday, October 19, 2007 9:23 AM
> To: 'Lars Eggert'
> Cc: Hancock, Robert; [e-mail]; [e-mail]
> Subject: RE: [PCN] Architecture draft - probing section & 
> general updates.
> 
> Hi Lars,
> 
> On the low agfgregation point, please see below: 
> 
> > -----Original Message-----
> > From: Lars Eggert [mailto:[e-mail]]
> > Sent: Friday, October 19, 2007 8:58 AM
> > To: Anna Charny (acharny)
> > Cc: Hancock, Robert; [e-mail]; [e-mail]
> > Subject: Re: [PCN] Architecture draft - probing section & general 
> > updates.
> > 
> > On 2007-10-16, at 21:55, ext Anna Charny (acharny) wrote:
> > > Yes, Robert's is a fair concern to which no obvious 
> solution is in 
> > > sight. Different equipment might use different algorithms 
> and might 
> > > use different fields for ECMP load-balancing under different 
> > > circumstances.
> > > IMHO this is a killer argument of why the use of probing for 
> > > discovering the state of ECMP paths should not be 
> considered within 
> > > the scope of PCN WG.
> > 
> > Agreed.
> > 
> > > There remains a question of whether probing can/should be
> > considerd to
> > > probe the path regardless of the ECMP issue.  I see most of
> > its value
> > > in flash crowd situations in combination with low ingress-egress 
> > > agregation.
> > 
> > I note that scenarios with low aggregation aren't in scope of the
> > charter:
> > 
> >    The initial scope of the PCN WG is restricted by the following
> >    assumptions:
> > ...
> >    (C) the number of flows across any potential aggregation 
> bottleneck
> >    is sufficiently large for stateless, statistical mechanisms
> >    to be effective
> 
> Actually,  I did not mean low aggregation *at the 
> bottleneck*, which is what the charter seems to restrict.  
> Rather I meant the case when the bottleneck has high 
> aggregation, but traffic on that bottleneck comes from a 
> large number of ingress-egress pairs, each having very low 
> aggregation levels.  I believe technically the charter does  NOT 
> put any explicit restrictions on the scope for ingress-egress 
> aggregation. 
> 
> Perhaps the WG should consider whether it is reasonable to 
> impose  restrictions on the *ingress-egress* aggregation 
> levels as well.  An argument can be made that in practice a 
> large number of ingress-egress pairs may only have a few 
> flows, even when the bottleneck aggregations are large. 
> 
> The decision on whether low ingress-egress aggregation level 
> is in scope seems to be important for choosing among the 
> various approaches proposed to the WG, as some of them are 
> substantially more sensitive to the low ingress-egress 
> aggregations than others (e.g. single marking does not 
> perform well at very low levels of aggregation, as we showed 
> at the last meeting).  
> 
> Perhaps an explicit discussion on the assumptions regarding 
> the expected levels of ingress-egress aggregations is needed 
> on the list? 
> 
> Towards that discussion, my personal view is that in the long 
> range ignoring low levels of ingress-egress aggregation 
> levels will severely limit the viability/usefulness of the 
> technology.  However, perhaps as an initial step it would be 
> OK to assume moderate to high aggregation levels, as long as 
> a clear path is visible on how to address low aggregations in 
> the future within the scope of defined behaviors.  But I 
> think it is important to have a clear consensus on this point. 
> 
> Anna 
> 
> > 
> > Lars
> > 


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