Subject: Re: [6lowpan] format document on the wiki

From: Philip Levis <[email-masked]>
Date: Tue, 5 Dec 2006 19:58:43 -0800

On Nov 29, 2006, at 12:47 PM, Schumacher Christian Peter Pii wrote:

> Dear Lowpanners.
>
> Does anyone have comments for the format document on the wiki?
>
> Are the current implementers happy with this draft?
>
> Please speak up.
>
First off, I like that NALP was changed to 00xxxxxx. It is unlikely  
that 6lowpan will need all the bits, and it enables many other  
networks to inexpensively and easily interoperate. Making it easier  
to interoperate decreases the cost of adoption. I am not an expert on  
IANA considerations: is arbitration of the 00xxxxxx values under its  
purview?

I have one concern with the current draft: the ordering of the  
fragmentation and mesh headers. In his presentation at IETF 67,  
Jonathan noted that the order followed the model presented by  
standard IPv6. In IPv6, fragmentation/reassembly must be end-to-end,  
so the ordering makes sense. However, this is sub-IP. I think that  
most of the real-world experiments with 15.4 radios, as well as basic  
loss models, suggest that per-hop fragmentation/reassembly is greatly  
preferable to e2e, particularly for energy reasons. You don't need to  
add a mesh header on each fragment, you have fewer retransmissions,  
and less state maintenance. Including a mesh routing header is  
essentially to provide IP routing; following the guidelines of RFC  
2460 Section 5, I believe the order of these two headers should be  
reversed: a node fragments and reassembles a mesh packet on a per-hop  
basis, rather than routing an IPv6 datagram one fragment at a time.

I've attached my simple C-based parsing code. It's not pretty and  
it's quite incomplete, but it covers the basic packet format  
considerations for the earlier draft.

Phil

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---

From: Daniel Park <[email-masked]>
Date: Mon, 11 Dec 2006 16:15:46 +0900

format document on the wikiTo WG, 

To me, I am still confusing the process of this issue.
Strictly speaking, I don't mind the format itself. Rather,
selecting one solution must happen as soon as possible.

I don't want to speak up at this stage. Before that, please
let us know the WG decision explicitely. Then, we will 
be able to come up with further details accordingly. In
fact, the document shown in wiki is not an official 
document. 

Nothing can be a perfect solution. But, simplicity
seems pretty much perfect approach. 

That's all at this stage in my mind.

Daniel (Soohong Daniel Park)
Mobile Convergence Laboratory, SAMSUNG Electronics.

----- Original Message ----- 
From: Schumacher Christian Peter Pii 
To: [email-masked] 
Cc: [email-masked] 
Sent: Thursday, November 30, 2006 5:47 AM
Subject: [6lowpan] format document on the wiki

Dear Lowpanners.

Please speak up.

Regards
Christian