Re: [Roll] Way forward for draft-clausen-lln-rpl-experiences

Thomas Heide Clausen <> Wed, 16 May 2012 13:17 UTC

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From: Thomas Heide Clausen <>
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Date: Wed, 16 May 2012 15:17:45 +0200
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To: JP Vasseur <>
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Cc: roll WG <>, Michael Richardson <>
Subject: Re: [Roll] Way forward for draft-clausen-lln-rpl-experiences
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On May 16, 2012, at 15:04 , JP Vasseur wrote:

> Dear Thomas,
> On May 16, 2012, at 2:08 PM, Thomas Heide Clausen wrote:
>> Dear JP and Michael,
>> Thank you for your mail.
>> On May 16, 2012, at 09:18 , JP Vasseur wrote:
>>> Dear Thomas,
>>> On May 11, 2012, at 8:25 AM, Thomas Heide Clausen wrote:
>>>> Dear JP, Michael, all
>>>> Upon JPs invitation, draft-clausen-lln-rpl-experiences was presented and discussed at the Paris meeting.
>>>> The authors consider the document complete and "done", and are looking to take it forward in the IETF 
>>>> process for publication as "Informational RFC" in the very near future. 
>>>> We would therefore like to ask the WG chairs, if the ROLL WG is willing to accept and progress this 
>>>> document towards publication?
>>> Thanks for your suggestion. So far we haven't see a lot of discussion/interest from the WG but your request is
>>> perfectly fair.
>> Thank you - I aim to be fair.
>>> So far there are no details on the scenarios and testing environments that led to the issues that 
>>> you reported, thus I would suggest you to first include them so that people interested could be able to reproduce
>>> it. Once the drat is updated, we'll be happy to pool the WG.
>>> Does that make sense ?
>> Not really. Let me explain my disagreement.
>> We tried RPL (and, I note, several different independent implementations of RPL) in a number of different scenarios and deployments, and observed the behaviors exhibited - noting that what we observed across the different implementations, scenarios and deployments was fairly universal.
>> We then went back to the specification, to understand these behaviors in detail, and understand their universality as independent from a specific scenario or deployment or implementation - but rather, as artifacts of the RPL protocol design.
>> We therefore believe that _any_ deployment, scenario or testing environment of RPL needs to pay attention to the issues presented, and find a way of addressing them. The way of addressing these issues in a given deployment or scenario would be appropriate for an "applicability statement" for that deployment or scenario.
> JP> Thanks for the clarification; that being said, for the WG to make sure that nothing is "scenario" dependent and the outcome could indeed apply to all scenarios,
> it might be worth being more explicit. For example, you pointed out to the MTU issue, to which I mentioned that 15.4g would bring a solution, so you may want to 
> explain that you did not use 15.4g 

This particular issue is fairly well pointed out in section 6, which references RFC4919 (cf section 2 hereof) - the particular "small MTU" is not dependent on the specific 127 octets of a specific L2, but a set of observations that RPL - when faced with a small MTU - may often not be able to carry a complete control message in a single fragment. Section 6, 3rd paragraph is fairly explicit as to this.

More globally, the draft cites - which (other than making specific reference to 802.15.4 (and not 15.4g) states that:

	"In most cases, LLNs will be employed over link layers with 
	 restricted frame-sizes, thus a routing protocol for LLNs should be
	 specifically adapted for such link layers

We observe some limits on RPL within the framework that the ROLL charter has set forth.

I'm not sure I see what more can be done to address this point.

> and there are a number of such examples ….

Personally, I do not believe that there are, but  we (I think I can speak for all the authors here) would very much appreciate your being explicit on these examples - least it's hard to discuss them. 


>> (For example, a deployment using only L2s which provides guaranteed bi-directional links  for L3 would address this by in the applicability statement stating "As all L2-links are guaranteed bi-directional, this addresses the issues raised in section 9 in draft-clausen-lln-rpl-experiences".)
>> Thus, we believe that it would actually be misleading (not to mention, unnecessarily verbose) to put the "details on the scenarios and testing environments" into this I-D.
>> Doing so would mislead the reader to believe that the issues presented only manifest themselves in those precise scenarios - which definitely isn't the case.
> JP> see the previous comment and tell us what you think; we could provide other examples.
> Note that we do not oppose to asking to the WG; we just request you first to add additional information to proceed forward.
> thanks.
> JP and Michael.
> JP.
>> Best,
>> Thomas
>>> Thanks.
>>> JP and Michael.
>>>> Best,
>>>> Thomas, Ulrich, Yuichi, Jiazi and Axel