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Re: [tsvwg] Deterministic Forwarding PHB

Brian E Carpenter <brian.e.carpenter@gmail.com> Thu, 06 March 2014 08:36 UTC

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Date: Thu, 06 Mar 2014 21:36:47 +1300
From: Brian E Carpenter <brian.e.carpenter@gmail.com>
Organization: University of Auckland
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To: "Shitanshu Shah (svshah)" <svshah@cisco.com>
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Cc: "Pascal Thubert (pthubert)" <pthubert@cisco.com>, "tsvwg@ietf.org" <tsvwg@ietf.org>
Subject: Re: [tsvwg] Deterministic Forwarding PHB
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Hi,

RFC 2475 provides 15 guidelines for new PHB specs. Can you
check that all of them have been considered in this draft?

One thing that is stated in RFC 2474 is that PHB specs should
be careful to describe behavior, not specify an algorithm. I think
that in a few places you actually start to specify an algorithm.

Whether a router that is handling many competing behaviors can
really respect your requirements (discard the packet if it
would be late) is not quite clear to me, but that is an
implementation issue. I would have thought you would always
have a small delta-T of uncertainty in the implementation.

    Brian

Regards
   Brian Carpenter
   http://orcid.org/0000-0001-7924-6182




On 04/03/2014 00:09, Shitanshu Shah (svshah) wrote:
> In the past discussion on LLN Diffserv recommendation (http://tools.ietf.org/html/draft-svshah-tsvwg-lln-diffserv-recommendations-02), we've shown most of the traffic categories, from different types of LL Networks, sharing similar characteristics of traditional IP networks, except traffic class (certain control signals) requiring deterministic forwarding service.
> 
> Though it was thought, at the time, that such deterministic service may be overloaded with the use of EF PHB (as currently described in http://tools.ietf.org/html/draft-svshah-tsvwg-lln-diffserv-recommendations-02 - not yet revised to make use of DF PHB), since then different L2 technologies are working on enhancing their capabilities for deterministic scheduled forwarding service. We think it is not appropriate to overload EF PHB definition. Forwarding service requirement for deterministic service clearly differs from that of EF PHB. More and more use–cases for end to end deterministic service means a need for us to define appropriate PHB to be used.
> 
> Thus we propose DF PHB.
> http://tools.ietf.org/html/draft-svshah-tsvwg-deterministic-forwarding-01
> 
> Thoughts from the wg? Comments/feed-back/suggestions?
> 
> Regards,
> Shitanshu
>

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