Re: [lp-wan] SCHC over LoRaWAN review

[<[e-mail]>]

Hello Laurent,

Having discussed it with the authors, I feel I can answer some of your questions.
The concatanation of the Fport byte and the few bits following constitute the Rule ID. The number of "few bits" is variable based on the first (Fport) byte, therefore we have a variable-length RuleID.
In order to be more in the spirit of the generic SCHC description draft, I suggest that the RuleID be described in the schc-over-LoRaWAN draft the following way

  *   The Rule ID is  of variable length
  *   The RuleID field spans the Fport byte and a few following bits of the LoRaWAN frame
  *   Only some values of the RuleID's most significant byte (=Fport) are allowed, namely  ...
  *   For each of these values, the RuleID is … bits long, the Rule is fragmentation or compression, etc …

Dominique

De : lp-wan <[e-mail]<mailto:[e-mail]>> on behalf of Laurent Toutain <[e-mail]<mailto:[e-mail]>>
Date : Wednesday 5 June 2019 17:26
À : lp-wan <[e-mail]<mailto:[e-mail]>>
Objet : [lp-wan] SCHC over LoRaWAN review

Dear Author,

As discussed during the interim, you will find some comments on the schc over LoRAWAN draft. I like the approach, but I have some questions about the way it is done.

- the draft should be more precise on the relation between FPort and RuleID. The first time I read the draft I thought that the FPort was the ruleID. What I understand after, tell me if it is true, the 3 FPort defined in the document are telling that the LoRaWAN PDU is a SCHC message.
- the relation between compression and fragmentation is not clear. The introduction describes a lot the compression and the rest of the document gives only rules for fragmentation.
if I understand well FPort 20 is for an implicit fragmentation rule and port 21 for any SCHC message starting with a ruleID. Why the document limits it to fragmentation?

- I don't understand either the reason to have 3 byte long tiles, why a so small value? Why for instance 6 cannot be used ?

The rest of the comments are in the world file with comments (sorry for that, if it causes trouble I will translate it into ascii).

Laurent

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