Re: [spring] TSV-ART review of draft-ietf-spring-segment-routing-msdc-08

Hey Martin,

Seeking your feedback here. Regarding Section 7.1, The intent of the
document is to describe one suggestive way and do not attempt to
standardize any suggested mechanisms based considering the Informational
nature. Authors do not attempt to fully solve – but to indicate how SR
helps towards this.The details of how the hosts figure out what paths to
take through the network such that the TCP and application are not affected
is outside the scope of this document.

Would you prefer to add perhaps - “details outside the scope” or “this is
one of the ways” or something else?

Cheers,

Gaurav

On Wed, Feb 14, 2018 at 8:47 PM, Gaurav Dawra <gdawra.ietf@gmail.com> wrote:

> Hey Martin,
>
> Sorry for late reply. Please see some comments inline[Gaurav]
>
> On Jan 9, 2018, at 2:25 PM, Martin Stiemerling <mls.ietf@gmail.com> wrote:
>
> Hi all,
>
> I've reviewed this document as part of the transport area review team's
> ongoing effort to review key IETF documents. These comments were written
> primarily for the transport area directors, but are copied to the
> document's authors for their information and to allow them to address any
> issues raised. When done at the time of IETF Last Call, the authors should
> consider this review together with any other last-call comments they
> receive. Please always CC tsv-art@… if you reply to or forward this
> review.
>
> Summary:
> This draft has serious issues in Section 7.1, 7.2 and in one part of
> Section3, described in the review, and needs to be rethought. The other
> sections are good AFAIK.
>
>
> Technicals:
> The overall draft looks ok, but the three points below look strange and
> need a fix before publication IMHO:
>
> Both Sections, 7.1. and 7.2., are describing ideas, but not well proven
> funcationality and not even safe to use functionality. Both are some sort
> discussing that different paths in the network could be used by the end
> host traffic. This sounds pretty much like the Path Aware Networking
> Proposed Research Group (https://irtf.org/panrg) and hints to the fact
> that there is no commonly understand and accepted engineering solution in
> this space.
>
> Section 7.1:
> [KANDULA04] is a really old reference that hasn't been followed up in
> recent times and even worse there is no evidence that this is going to work
> good enough or stable enough under real Internet traffic. Additionally, it
> is more than unclear how any modern TCP implementation will react to this
>
> [Gaurav] Will get back on this.
>
>
> Section 7.2:
> This section describes an idea without detailing too much about any
> further aspects. Further it changes the commonly accepted notion of what an
> end host can do with the network. At best this would require a good
> definition of what an end host in your setting is, e.g., a highly modified
> piece of (at least) software that usually not found in OS availble on the
> market (yet?)
> Further communicating instantaneous path characteristics to a central
> point is potentially a bad idea, as the data is already outdated when
> reported by any node.
>
> [Gaurav] I believe Authors are trying to highlight that Host which is
> defined in (https://tools.ietf.org/html/draft-ietf-spring-segment-
> routing-15) can influence the traffic based on the Calculations locally
> or jointly with the controller. Implementations can decide how much
> Centralized -vs- localized control is allowed at Host based on performance
> data collection.
>
>
> Section 3, 3rd bullet point:
> It is the foundation of TCP that the network is regarded as a black box
> and that you infer from the transmission of packets what the current state
> of the network path is. Inferring network path metrics (you mention SRTT,
> MSS, CWND ) is a bad idea, as this would required that all paths exhibit
> this and if not what is going to happen?
> It could be an interesting research field to change many points in TCP's
> behavior, but this once again points to the fact that this not the IETF
> works but IRTF or elsewhere.
>
> [Gaurav] Martin, Authors are trying to suggest that TCP is rightly
> treating Network as Black Box. Authors are implying per path performance
> metrics as not cached. Is there some change in text you are suggesting?
>
> Cheers,
>
> Gaurav
>
>
> Kind regards,
>
>  Martin
>
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