Do you mean that 6LoWPAN in RIOT does not support lost fragment recovery? Assuming it does, what I had in mind was that we could segment data in the application to the IP MTU and leverage the lost fragment recovery feature in 6LoWPAN to get a decent performance. This way we may not need to implement lost segment recovery in the application. But if 6LoWPAN in RIOT does not support recovery of lost fragments we might as well run our application direclty on link layer (since we dont need IP routing).
there had been proposals in 6LowPan + Roll by Pascal Thubert for adding reliability to 6LowPan (recovering fragments) ... but if I see things correctly, they have never gotten anywhere -> Carsten?
In any case, the design discussion seems a bit out of focus: Whether to design a L2 protocol or an application layer (on top of CoAP) should be sorted out first. I guess these things depend on the problem scope and the objectives.
Martine, actually when I wrote the question I did not mean to imply that the 6LoWPAN standard has "lost fragment recovery". I did a quick search on it and I see no RFCs. Thanks for pointing it out.
Thomas, I agree that whether we do it on L2 or on the application layer depends on the problem scope. We are working on a prototype and would like to get things running with a decent performance in time. Hence the questions about what RIOT supports and what not. Perhaps we need to do some loss recovery implementation at the application layer to not have a poorly performing prototype.