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

Jiazi Yi <> Wed, 16 May 2012 13:36 UTC

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From: Jiazi Yi <>
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Date: Wed, 16 May 2012 15:36:33 +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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Hi dear JP,

On May 16, 2012, at 3:04 PM, 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 and there are a number of such examples ….

The document is based on the common scenarios of LLN, which means: constrained power, memory, energy, etc. 
In another words, it's "LLN-scenario" dependent. 

For example, regarding the MTU issue, it is said in the ROLL WG charter:

	- 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.

and in RFC 4919, the first characteristic of 6lowpan listed:

   1.   Small packet size.  Given that the maximum physical layer packet
        is 127 bytes, the resulting maximum frame size at the media
        access control layer is 102 octets.  Link-layer security imposes
        further overhead, which in the maximum case (21 octets of
        overhead in the AES-CCM-128 case, versus 9 and 13 for AES-CCM-32
        and AES-CCM-64, respectively), leaves 81 octets for data

More assumptions can be found in documents of 6lowpan and roll. Therefore, IMHO, it's safe to build the experience document based on those common assumptions. In contrast, it will be verbose to list all the possible special solutions/technologies. 


YI Jiazi
Hipercom@LIX, Ecole Polytechnique
Route de Saclay 91128 Palaiseau Cedex France

>> (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
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