Re: Drops in Core

["Patrick W. Gilmore" <patrick () ianai net>]

On Aug 15, 2015, at 1:41 PM, Job Snijders <job () instituut net> wrote:
> On Sat, Aug 15, 2015 at 11:01:56PM +0530, Glen Kent wrote:

> > Is there a paper or a presentation that discusses the drops in the core?
> >
> > If i were to break the total path into three legs -- the first, middle
> > and the last, then are you saying that the probability of packet loss
> > is perhaps 1/3 in each leg (because the packet passes through
> > different IXes).
>
> It is unlikely packets pass through an IXP more then once.

“Unlikely”? That’s putting it mildly.

Unless someone is selling transit over an IX, I do not see how it can happen. And I would characterize transit over 
IXes far more pessimistically than “unlikely”.


[Combining responses]
On Aug 15, 2015, at 1:21 PM, Owen DeLong <owen () delong com> wrote:
> I would say that the probability of a packet drop at any particular peering
> point is less than the probability at one of the two edges.
>
> However, given that most packets are likely to traverse multiple peering
> points between the two edges, the probability of a packet drop along
> the way at one of the several peering points overall is roughly equal
> to the probability of a drop at one of the two edges.

I’m a little confused why most packets are “likely to traverse multiple peering points”?

Most packets these days are sourced from one of three companies. (Which Owen should know well. :) At least one of those 
companies published stats saying the vast majority of packets are “zero or one” AS hop from the destination. I cannot 
imagine Google or Netflix being 50% behind Akamai on that stat. Which clearly implies most packets traverse “zero or 
one” AS hop - i.e. one or zero peering points.

Finally, I would love to see data backing up the statement that packets are more likely to drop at one edge (assuming 
the destination?) than at a peering point.

-- 
TTFN,
patrick