Re: [tsvwg] NQB - which DSCP to recommend?

Sebastian Moeller <moeller0@gmx.de> Fri, 15 November 2019 08:40 UTC

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From: Sebastian Moeller <moeller0@gmx.de>
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Date: Fri, 15 Nov 2019 09:35:16 +0100
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To: "Black, David" <David.Black@dell.com>
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Subject: Re: [tsvwg] NQB - which DSCP to recommend?
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Hi David,


> On Nov 15, 2019, at 01:58, Black, David <David.Black@dell.com> wrote:
> 
> Lurking in the lengthy discussion about NQB and existing WiFi is a topic that needs broader WG attention, please.   Sebastian wrote:
>  
> > IMHO the upshot of this should be to 
> > 
> > a)  propose a DSCP for the NQB PHB that maps into AC_BE
>  
> The general topic is which DSCP should be the recommended DSCP for the  NQB PHB.  The NQB draft proposes 0x2A, but the WG may choose to select a different DSCP for this purpose.
>  
> Ok, please discuss …

	[SM] I propose to use 0x6 (000110) as DSCP for the NQB PHB on un-charcaterized networks, and to use 0x6A (101110) if the receiving network is known to contain NQB compatible wifi elements (or that network operator requested the re-mapping) as re-mapping to 0x6A (101110) will by default get packets into the desired AC_VI. 

	According to https://datatracker.ietf.org/meeting/99/materials/slides-99-tsvwg-sessb-31measurements-concerning-the-dscp-for-a-le-phb-00 partial bleaching can re-map a few common PHBs into the same DSCP (occurrence of partial bleach reported ~10%). But out of the "common" DSCPs only AF13, AF23, AF33, AF43, and EF carry 110 in their low three bits, and since all of the denote high priority (which partially indicates a request for low latency) this re-mapping does not see catastrophic and it certainly does carry the same cause priority inversion concerns that were relevant in selecting the LE PHB DSCP (https://tools.ietf.org/html/rfc8622). 

	I believe this to be a viable path forward that a) protects unsuspecting wifi networks from unintended side-effects of inceasing the use of AC_VI, yet b) allows ISPs to roll-out APs/wifi-routers equipped to handle NQB in the desired fashion. (By using a construct like hostapd's qos_map NQB-aware APs should even be able to instruct stations to map 0x6 into AC_VI if that should be desired).


Best Regards
	Sebastian


>  
> Thanks, --David
> ----------------------------------------------------------------
> David L. Black, Senior Distinguished Engineer
> Dell EMC, 176 South St., Hopkinton, MA  01748
> +1 (774) 350-9323 New    Mobile: +1 (978) 394-7754
> David.Black@dell.com
> ----------------------------------------------------------------