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

["Georgios Karagiannis" <[e-mail]>]

Hi all

Before taking any decisions I would like to emphasize the following.

In my opinion preferential dropping of any kind increases the complexity
in the interior routers. Furthermore, when excess rate mechanisms are
used,
by preferentially dropping marked packets it severely decreases the
robustness of the PCN domain operation.
With robustness I mean, that due to a corner case or due to a
msiconfiguration the operation of the PCN domain will
completely collapse.
This is because the admission control trigger (CLE) at the egress is 
much more sensistive when marked packets are dropped than either the
situation that unmarked and marked packets are dropped randomly (current
implementation of routers) or the situation that unmarked packets are
dropped.
Therefore, as an initial step is better to do not change the current
router behaviour from the preferential dropping point of view.

Regarding LC-PCN and 3SM operation at the core, the only requirements
that have to be supported are:

* use current router behaviour from the preferential dropping point of
view.
Thus drop marked and unmarked packets randomly. Do not preferentially
drop marked packets.

* use a parameter N (or S) that should be equal in whole PCN domain.
The only change in the token bucket implementation will be that the token
bucket should mark N packet (or bytes) instead of marking one packet (or
byte). Note that if N = 1, then the token bucket operates the same as
described in the SM draft. If N > 1, then the SM scheme can operate in
the same way with the difference that the measured excess rate at the
egress should be multipleied with N.

All the other optimization features that are described in the LC-PCN
draft are optional.

Best regards,
Georgios




On 3/14/2008, "Steven Blake" <[e-mail]> 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).
>
>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)?
>
>Q3: Does the working group have enough information to make a decision
>    about the way forward for the standards-track PCN scheme?
>
>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
>
>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
>
>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)?
>
>
>Please send comments to the list.
>
>
>Regards,
>
>=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
>Steven Blake                <[e-mail]>
>Ericsson/Redback Networks               [phone]
>
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