Re: [PCN] Concensus questions from Thursday's PCN meeting

[Michael Menth <[e-mail]>]

I mean

http://www.ietf.org/mail-archive/web/pcn/current/msg01387.html

instead of

http://www.ietf.org/mail-archive/web/pcn/current/msg01386.html

See inline!

Michael Menth wrote:
> Hi,
>
> sorry for being late ...
>
> Steven Blake wrote:
>   
>> Greetings.
>>
>> There were six concensus questions called during yesterday's PCN
>> meeting.  Before we call the questions on the list, I want to paraphrase
>> them and make sure that everyone agrees that this captures the sense of
>> the discussion.
>>
>>
>> Q1: As an initial standardization activity, should the PCN wg produce a
>>     standards-track PCN scheme that requires only two encoding states?
>>     (Note: this question does not presume that the solution is Single
>>     Marking).
>>   
>>     
>
> Yes, it seems necessary due to missing approved alternatives. However, I 
> find the new encoding proposal in
> http://www.ietf.org/mail-archive/web/pcn/current/msg01386.html
>   
I mean http://www.ietf.org/mail-archive/web/pcn/current/msg01387.html

> quite appealing as it achieves both admission control and flow 
> termination with a single DSCP. I think it is worthwhile to be discussed 
> as an alternative for an encoding scheme requiring a single DSCP which 
> seems to be our major constraint.
>
>   
>> Q2: Should the PCN wg produce an experimental-track extension to the
>>     standards-track PCN scheme that requires another encoding state (for
>>     a total of three encoding states)?
>>   
>>     
>
> Yes, it seems to allow for significantly improved PCN performance.
>
>   
>> Q3: Does the working group have enough information to make a decision
>>     about the way forward for the standards-track PCN scheme?
>>   
>>     
>
> Yes - after 
> http://www.ietf.org/mail-archive/web/pcn/current/msg01386.html
I mean http://www.ietf.org/mail-archive/web/pcn/current/msg01387.html

>  only partly.
>
> It seems to be consensus that
> * AC based on excess rate marking with regard to the admissible rate 
> cannot reliably deal with small ingress-egress aggregates in the order 
> of 10 flows
> * We will have many small ingress-egress aggregates in the future that 
> are even smaller
> http://www.ietf.org/mail-archive/web/pcn/current/msg00831.html
> * FT based on excess rate marking with regard to the admissible rate 
> does not reliably work with ECMP
>    - FT cannot always detect when strong pre-congestion occurs 
> (u*admissible rate due to signal dilution)
>    - FT cannot tear down only the right flows such that the termination 
> process requires several termination steps
>    - This issue is a matter of traffic distribution under failure 
> conditions and cannot be solved by overprovisioning unless making the 
> need for FT obsolete.
> * ECMP is a reality in many of today's networks to achieve fast reroute 
> for ingress-egress pairs that have multiple paths.
>
> However, I feel that there is not yet a clear idea what the standards 
> track PCN with two codepoints is used for:
> * admission control (AC) and flow termination (FT) based on excess 
> marking with regard to an admissible rate
> * only admission control with threshold marking with regard to an 
> admissible rate
>
> The new encoding proposal in
> http://www.ietf.org/mail-archive/web/pcn/current/msg01386.html
> seems to allow both AC based on threshold marking and FT based on excess 
> marking at the expense of requiring probe packets to support admission 
> decisions.
>
>   
>> Q4: Should the standards-track PCN scheme require (as a MUST implement
>>     feature) that interior PCN routers support Excess-Rate marking,
>>     according to the particular method of handling already marked 
>>     packets and drops described in Anna Charny's presentation?
>>     http://www3.ietf.org/proceedings/08mar/slides/pcn-6.pdf
>>   
>>     
>
> Yes. But it ALSO requires the option for preferential dropping of marked 
> packets and an option for random drops with equal importance. As long as 
> the edge behavior is not clear yet, no decision about preferential 
> dropping can be made. Furthermore, packet size independent marking 
> (PSIM) as described in
> http://tools.ietf.org/wg/pcn/draft-menth-pcn-emft-00.txt
> is useful to implement because the fairness of any flow termination 
> scheme making use of marked packets to indicate flows to be terminated 
> profits from this feature. Evidence for that is documented in
> http://www.ietf.org/internet-drafts/draft-menth-pcn-performance-02.txt
> or
> http://www3.informatik.uni-wuerzburg.de/staff/menth/Publications/Menth08-PCN-MFT.pdf 
>
> This also applies to potential improvements of SM.
>
>   
>> Q5: Should the standards-track PCN scheme require (as a MUST implement
>>     feature) that interior PCN routers support Threshold marking (in
>>     addition to Excess-Rate marking), according to the particular method
>>     described in Philip Eardley's presentation on Tuesday?
>>     http://www3.ietf.org/proceedings/08mar/slides/pcn-4.pdf
>>   
>>     
> Yes.
>
>   
>> Q6: If presented with sufficient evidence in a timely fashion, would
>>     the PCN wg entertain the option of modifying the interior router
>>     Excess-Rate marking behavior for the standards-track PCN scheme (as
>>     described in question 4)?
>>   
>>     
> Yes.
>
> Regards,
>
>     Michael
>
>   
>> Please send comments to the list.
>>
>>
>> Regards,
>>
>> =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
>> Steven Blake                <[e-mail]>
>> Ericsson/Redback Networks               [phone]
>>
>> _______________________________________________
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>> https://www.ietf.org/mailman/listinfo/pcn
>>   
>>     
>
>   

-- 
Dr. Michael Menth, Assistant Professor
University of Wuerzburg, Institute of Computer Science
Am Hubland, D-97074 Wuerzburg, Germany, room B206
phone: [phone], fax: [phone]
mailto:[e-mail]
http://www3.informatik.uni-wuerzburg.de/research/ngn

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