Re: [tsvwg] draft diffserv-intercon: Handling of a scavenger class / CS1

[Mikael Abrahamsson <[e-mail]>]

On Sat, 30 May 2015, Brian E Carpenter wrote:

> Firstly, note that RFC 3662 is very intentionally not standards-track and
> does not recommend a DSCP value. To me, this discussion seems to mix up two
> orthogonal concepts:
>
> 1. What the PHB for a scavenger class actually is (or in Mikael's
> suggestion to AQM, what the PHB set is, since mention of priority
> implies several members of a PHB set, like AFxy).
>
> 2. What DSCP values happen to be used for this PHB set. Despite
> the confusion introduced by RFC 3662, those values don't have to
> ones already used for other purposes, especially not CSx. Actually
> the text makes it clear that the DSCPs recommended for AFxy should
> be considered:
>
>   If a CS PHB is used, note that this configuration will violate the
>   "SHOULD" of section 4.2.2.2 of RFC 2474 [RFC2474] since CS1 will have
>   a less timely forwarding than CS0.  An operator's goal of providing
>   an LE PDB is sufficient cause for violating the SHOULD.  If an AF PHB
>   is used, it must be configured and a DSCP assigned such that it does
>   not violate the "MUST" of paragraph three of section 2 of RFC 2597
>   [RFC2597] which provides for a "minimum amount of forwarding
>   resources".

I was only talking about what the 6 DSCP bits should be for this to ever 
start to work widely across the Internet. My suggestion is 000xx0 and the 
recommendation is to only bleach the first three bits at ISP interconnects 
instead of all 6 bits (which is the most commonly done at this time). This 
is backwards compatible with CS0/BE and it's also backwards compatible 
with default queuing behaviour when doing automatic IP precedence -> 
802.1p and the recommended 4 queue ethernet prioritization (where CS1 and 
CS2 is lower than CS0 and CS3).

-- 
Mikael Abrahamsson    email: [e-mail]