Dear Samita : From: Samita Chakrabarti [mailto:[email protected]]
Hello : I am trying to decipher the RFC 8025 packet header sequence and bit patterns from reading the document and http://www.iana.org/assignments/_6lowpan-parameters/. Sorry, I should have asked these questions before, but it is never too late... * I assume the main purpose is to give the implementor tools to go and parse/interprete additional data carried by original RFC 4944 style packet or not. [Pascal] Yes, we have a very large space now. * The document says that the page-switch dispatch type should be always preceded by mesh and fragment header. I would assume that original pg 0 or LOWPAN-IPHC dispatch type can precede as well. Can some one confirm if the following sequences are valid ? [Pascal] The page 0 switch is implicit and placed before the mesh header, which is defined in that page. There can be a packet without a mesh or a fragment header, so a page switch is not always preceded by one of those. But if one of those headers is present, then it appears before switching to another page. 1) [Mesh][page-switch-to-X][New-dispatch-type from page X][Payload] [Pascal] Valid 2) [ESC][ESC-Bytes][LOWPAN_IPHC][page-switch-to-X][Page-X-dispatch][Payload] [Pascal] I expect that this could happen with an update of RFC 6282, but with the current spec you cannot since RFC6282 defines the chain all the way to the payload or at least the end of the compressed piece. 3) [LOWPAN-IPHC][Payload][page-switch-toX][Page-X-dispatch][additional-payload] [Pascal] Then again this could happen but would need new specs If both 2 and 3 are valid sequences, can you please provide two examples of use-cases ? [Pascal] It could potentially be used for selectively compressing or signing the payload; but I’m not aware of anyone trying this. It could also be used for packaging separate fragments back together or something. I do hope that no one ever specifies this based on what I heard from MP-TCP and middle box games. The most common sequence involving RFC 8025 would be [page-switch-to-Page1] [6LoRH]* [LOWPAN-IPHC] [IPv6 headers]* [LOWPAN-NHC] [Payload] I was not sure if we can allow payload with each page and parse multiple payloads with the same packet [ assuming we have large enough frame size]. [Pascal] The paging does not say, but new specs using it would. Take care, Pascal Thanks, -Samita
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