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

[<[e-mail]>]

Greg,

the situation I'm in is:
- DiffServ is deployed since more than a decade and multiple DSCP are used
- DiffServ compliant interconnection works with re-marking as an operational commodity. RFC 8100 is deployed.
- The Layer 2 and Layer 3 access Wholesale market over here is regulated and that partially includes specification 
  of access network DSCPs and corresponding Ethernet priorities. 
- I suggest to use a 000xxx DSCP, if a DSCP identifying a specified PHB not requiring an SLA at interconnection 
  should arrive a customer access with an unchanged DSCP. 

At an Interconnection point of the backbone that I'm working with, a DSCP 101xxx is interpreted as Telephony traffic. If there's an SLA in place, the EF PHB is honored and suitable charges apply. If there's no SLA in place, this traffic continues being transported by the default PHB and will be marked appropriately.

Standardised E2E PHBs are a good idea, but DiffServ isn't greenfield. To me, changes in the DiffServ architecture (like standard E2E DSCPs) must respect operational deployments at interconnection. I don't think that's simple, but it may be possible, if all parties involved can agree on a joint way forward.

Regards,

Ruediger

-----Ursprüngliche Nachricht-----
Von: Greg White <[e-mail]> 
Gesendet: Samstag, 16. November 2019 08:25
An: Geib, Rüdiger <[e-mail]>; [e-mail]; [e-mail]
Cc: [e-mail]
Betreff: Re: [tsvwg] NQB - which DSCP to recommend?

TSVWG-ers,

We are proposing this PHB and a standardized DSCP that maps to AC_VI because we believe that it will provide a real benefit to residential broadband end-users worldwide (and our experimental usage to date has shown this to be true).   I believe the risk of unsuspecting users suffering as a result is entirely overblown.  I think the only thing that we agree on in that regard is that if the WiFi link is the bottleneck and if massive amounts of NQB marked traffic are delivered to the home network, it is possible to impact Default traffic.  But to have this occur in practice assumes that ISPs don't care about their customers, and are perfectly happy creating situations that result in trouble calls and/or truck rolls.  No ISP that I am aware of is interested in making their customers angry and adding to their operations costs.

Regardless of which DSCP the IETF selects, an ISP uninterested in providing the benefits of NQB to their customers (or one that is oblivious to NQB) can simply leave existing bleaching in place. 

If Sebastian's proposal is adopted, let's examine how this might play out.

An ISP interested in providing the benefits of NQB to their customers would presumably want to map 0x06 to AC_VI or AC_VO, so that the benefits are not lost when the traffic crosses a WiFi link. They could do this in ISP-provided gateways (either implementing a DSCP remapping, or using QOS_MAP), the upshot being that users of non-ISP-provided gateways fail to get the benefit of NQB.  Yes, they would be protected from the remote possibility of harm, but at a cost.   Another possible outcome is that an ISP remaps all NQB traffic to (e.g.) 0x2A in their core network, and this 0x06 value is only used across interconnects.  Since work would be needed on PE routers to turn off ingress bleaching of the NQB codepoint anyway, that seems like it might be the easiest place to map it to 0x2A.  Another possible outcome is that NQB applications ignore the IETF DSCP recommendation, and end up using a de facto DSCP in its place (possibly 0x2A), one that gets the benefit of segregated queuing provided by AC_VI (or AC_VO) across a broader user base, without creating remapping requirements for ISPs.  This would almost certainly be the case for uplink NQB traffic.

The latter two possibilities would result in NQB traffic arriving in all of the ISP's customers' home WiFi networks such that it maps to AC_VI or AC_VO anyway.  In cable access equipment, per-user bleaching of NQB traffic is straightforward, whereas per-user per-DSCP re-mapping isn't, so this approach would allow the ISP the ability to selectively enable/disable NQB marking on a per-user basis if need be.

The first option strikes me as being less likely anyway, since it involves new feature development on home routers.  Many ISPs do not write their own home router implementations.  

In all cases the ISP needs to ensure that supporting NQB on downlink traffic benefits their customers in the end.  This involves some type of control/policing of the NQB marking. This could be via traffic protection implemented on PHB compliant links, or it could be via other policies implemented in other network elements.

It seems to me that Sebastian's proposal simply creates a barrier to deployment and/or a degradation of the relevance of the IETF recommended DSCP, but no real protections.   

In my view, the sought after protections come instead from giving ISPs guidance on avoiding the potential for harm in WiFi networks that use existing equipment, as well as recommendations for upgrades to WiFi equipment to enable full PHB support (including traffic protection).  I am comfortable with David's suggestion to mandate that NQB PHB equipment that provides residential broadband service be capable of bleaching NQB to Default.  

I stand by the original proposal to assign 0x2A.

Greg



On 11/15/19, 2:27 AM, "tsvwg on behalf of [e-mail]" <[e-mail] on behalf of [e-mail]> wrote:

    Hi Sebastian, hi David
    
    I agree with your analysis. I don't object your proposed DSCP. Should there be a desire to circumvent the situation you describe, 000111 (or another spare 000dd1 DSCP) might be an option. As said, proposed only for the case that your suggestion doesn't reach consensus.
    
    Regards,
    
    Ruediger
    
    -----Ursprüngliche Nachricht-----
    Von: tsvwg <[e-mail]> Im Auftrag von Sebastian Moeller
    Gesendet: Freitag, 15. November 2019 09:35
    An: Black, David <[e-mail]>
    Cc: [e-mail]
    Betreff: Re: [tsvwg] NQB - which DSCP to recommend?
    
    Hi David,
    
    
    > On Nov 15, 2019, at 01:58, Black, David <[e-mail]> 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
    > [phone] New    Mobile: [phone]
    > [e-mail]
    > ----------------------------------------------------------------