Re: [tsvwg] Doubts regarding motivation of draft-ietf-tsvwg-iana-dscp-registry-04

["Bless, Roland (TM)" <[e-mail]>]

Hi Sasha,

Am 08.05.2018 um 09:56 schrieb Alexander Vainshtein:
> I have looked up the draft
> <https://tools.ietf.org/html/draft-ietf-tsvwg-iana-dscp-registry-04>,
> and I have doubts regarding validity of its motivation.
> 
> The draft says – correctly -that 22 out of 32 values in Pool 1 of the
> DSCP code points have been already assigned, therefore it considers this
> pool as nearly exhausted.
> 
> What the draft does not say that, out of these 22 assignments, 2o have
> been done in 1998 and one – in 1999. Only one assignment has been
> requested in the past 19 years, and no assignments have been requested
> after 2010.

> At this rate my estimate is that Pool 1 would suffice for the next 50+
> years without its exhaustion becoming an issue. So why should the IETF
> do anything */now/*?

This is motivated in section 1:

   The rationale for this update is a need
   to assign codepoints for particular PHBs that are unable to use any
   of the unassigned values in Pool 1.

This problem is caused by implementations that
do IP precedence bleaching (i.e., zeroing the
top three bits of the DSCP) thereby rewriting
(or unintentionally mapping) DSCP values to other
DSCP values. This is a problem for the mentioned
LE PHB I-D https://tools.ietf.org/html/draft-ietf-tsvwg-le-phb
It is possible that some other standardized DSCPs get mapped to
the LE PHB DSCP if the LE DSCP were taken from the DSCP standards
action pool 1 (xxxxx0).

There are measurements and more background material for this:
https://datatracker.ietf.org/meeting/99/materials/slides-99-tsvwg-sessb-31measurements-concerning-the-dscp-for-a-le-phb-00
https://www.ietf.org/proceedings/96/slides/slides-96-maprg-6.pdf

Regards,
 Roland