Subject: Diff serv over MPLS

From: Francis Arts <[email-masked]>
Date: Fri, 16 Mar 2001 18:11:18 +0100

Hello Francois, Liwen, ...,

I have a question concerning the latest version of the 'diff serv over
MPLS' draft. For L-LSPs the drop precedence is encoded in the exp bits.
Compared to version 7 of the draft the encoding of the color 'red' has
changed from 01 to 11.

Why was this encoding changed?

[If changing the encoding of the drop precedence would be done, I would
have expected that the encoding of ALL  (...) drop precedence values
would have changed to align with the recommended DSCPs for the AF PHB:
* 01 = green.
* 10 = yellow.
* 11 = red.]

Kind regards,

    Francis.

---

From: Francois Le Faucheur <[email-masked]>
Date: Tue, 20 Mar 2001 12:28:27 +0100

Francis,

hey, just on time for the end of the Last Call...

>Why was this encoding changed?

encoding was changed for the following reason: 
* L-LSPs EXP<-->PHB mapping
=========================
>We plan to incorporate Jim Murphy's suggestion to modify the EXP value
>corresponding to AFn3 L-LSPs. AFn3 would be mapped to EXP=011 (instead of
>010).
>For memory, the rationale is that implementations which support only two
>drop priorities per AF class could determine the drop priority to be
>applied by looking at a single bit. Same idea was used for the DSCP
>encodings for AF.
>

so, motivation is to have one single bit that can be checked for 
yellow_or_red.

apart from that, absolute values don't really matter; 
but I agree that we may as well use the same value as AF DSCP "drop bits".
-09 will use EXP= 001, 010, 011.

Thanks

Francois