Re: [Roll] [6lo] [6tisch] Proposed improvement in RH3-6LoRH
Simon Duquennoy <simonduq@sics.se> Tue, 19 January 2016 17:53 UTC
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From: Simon Duquennoy <simonduq@sics.se>
To: Tengfei Chang <tengfei.chang@gmail.com>
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Cc: Routing Over Low power and Lossy networks <roll@ietf.org>, "6tisch@ietf.org" <6tisch@ietf.org>, "6lo@ietf.org" <6lo@ietf.org>
Subject: Re: [Roll] [6lo] [6tisch] Proposed improvement in RH3-6LoRH
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Hi Pascal, One thing that bugs me is that RH3-6LoRH seems to be an alternative to RH3 rather than a strict compression of it. For instance, a RH3 using different cmpri and cmpre values, or using non power-of-two, can not be compressed with 6LoRH. And the discussion on copying the prefix form the DAG root is also a departure from RH3. Am I missing something? Thanks, Simon On Tue, Jan 19, 2016 at 1:59 PM, Tengfei Chang <tengfei.chang@gmail.com> wrote: > Hello Pascal, > > Thanks a lot for the detailed answer! I think it solves all my concern. I > will vote for it! > > Tengfei > > > > On Tue, Jan 19, 2016 at 11:00 AM, Pascal Thubert (pthubert) < > pthubert@cisco.com> wrote: > >> Hello Tengfei: >> >> >> >> Basically the change proposal accounts for the assumption that the last >> segment may be different, which comes with the idea of supporting non RPL >> leaves. If you look at it the original RH4 (RFC 6554) makes a difference >> for the last hop. >> >> >> >> Also, the root is the one computing the 6LoRH so it is easier for it to >> take its own address as reference. >> >> >> >> Finally the text is unclear about which bits from the destination are to >> be used. >> >> >> >> All in all, using the root as reference makes more sense than using the >> final destination as I had initially proposed. So the new proposal is not a >> merge but an instead, with clarifying text about the process I showed in >> the picture. >> >> >> >> More answers inline: >> >> Dear all >> >> >> >> The picture below illustrates how the RH3 6LoRH works with draft 03 in a >> case like Root -> A -> B -> C -> leaf >> >> >> >> [image: cid:image001.png@01D152A0.1C780E10] >> >> >> >> The first 6LoRH is expected to be a full address (128 bits) to set up a >> reference and the next 6LoRH are expected to be smaller and just override >> the rightmost bits which form the delta from the reference. >> >> >> >> What if the B and C address can be compressed to one byte(RH3-6LoRH type >> 0)? >> >> When leaving the root the format would like: >> >> *RH3-6LoRH type 4 IPv6 Prefix (64bits) A's suffix (64bits) >> RH3-6LoRH type 0 B's suffix (8bits) C's suffix (8bits)* >> >> >> >> Ø Pascal If A’s address is the same as B and C for the first 120 bits >> then this format is correct : )> Pascal >> >> >> >> >> >> >> >> should node A need to extend the address of B address when the packet >> leaving A? Like: >> >> *RH3-6LoRH type 4 IPv6 Prefix (64bits) B's suffix (64bits) >> RH3-6LoRH type 0 C's suffix (8bits)* >> >> >> >> Ø Pascal: That is correct. Note that there is no separation between >> prefix in suffix in the type 4. So the drawing applies for all types if you >> consider that the prefix length is 64, 96, 112 or 120 depending on the type >> of the next RH. With the proposal, if the root has the same /120 prefix as >> A, B and C then we have a single type 0 with A, B and C in it. >> >> Proposal: we could consider that the 128bits source of the IP header >> before the RH3 is the reference to start with. >> >> I have no comments with the proposal. Just want to mention in the >> currently version of draft (version 3) , it says : (in section 5) >> >> ... >> >> If some bits of the first address in the RH3-6LoRH header can be >> >> derived from the final destination in the LoWPAN_IPHC, then that >> >> address may be compressed; otherwise it is expressed as a full IPv6 >> >> address of 128 bits. Next addresses only need to express the delta >> >> from the previous address. >> >> ... >> >> How to understand this combining with the proposal? (Or this is the point >> we are going to replace by the proposal? Let me know) >> >> >> >> Ø Pascal: proposal is to replace. That text was unclear and more >> complex to implement. And fails to optimize for leaves that are not >> configured like the mesh. >> >> With that even the first hop could be compressed the same way as the >> other hops. With RPL, the root is the encapsulator if IP in IP in used. >> Good thing, in that case the root is totally elided with the IP-in-IP 6LoRH. >> >> That's great! Could I confirm when the packet is inside a RPL domain >> where IP in IP is elided, the source destination in IPHC is the reference? >> >> Ø Pascal: Yes. The only case where IP in IP is elided is when the >> source is the root. The root would still be the reference. The text I >> proposed says the Source of the header that is placed before the RH3, and I >> meant in the non-compressed form. With RPL as it stands today this is >> always the root. >> >> So this simple proposal saves up to 16 octets (that’s in the case with a >> single subnet and all addresses differ only by the last 2 bytes). I’m >> willing to add it in the next revision. >> >> I don't know how to calculate the saved bytes. For this case, will the >> format looks like this? >> >> RH3-6LoRH type 1 A's suffix (16bits) B's suffix (16bits) C's >> suffix (16bits) >> >> Ø Pascal: Yes. In that case you save 14 bytes in A’s address plus the >> RH3-6LoRH type 4 which is 2 additional bytes, 16 total. >> >> Any opposition? >> >> >> >> Pascal >> >> >> >> Thanks for the proposal! >> >> >> >> >> >> Ø Pascal: Do you vote for it? I’m asking because the plugtest is coming. >> >> >> _______________________________________________ >> 6tisch mailing list >> 6tisch@ietf.org >> https://www.ietf.org/mailman/listinfo/6tisch >> >> >> > > > _______________________________________________ > 6lo mailing list > 6lo@ietf.org > https://www.ietf.org/mailman/listinfo/6lo > >
- [Roll] Proposed improvement in RH3-6LoRH Pascal Thubert (pthubert)
- Re: [Roll] [6tisch] Proposed improvement in RH3-6… Tengfei Chang
- Re: [Roll] [6tisch] Proposed improvement in RH3-6… Pascal Thubert (pthubert)
- Re: [Roll] [6tisch] Proposed improvement in RH3-6… Tengfei Chang
- Re: [Roll] [6lo] [6tisch] Proposed improvement in… Simon Duquennoy
- Re: [Roll] [6lo] [6tisch] Proposed improvement in… Simon Duquennoy
- Re: [Roll] [6tisch] [6lo] Proposed improvement in… Michael Richardson
- Re: [Roll] [6tisch] [6lo] Proposed improvement in… Simon Duquennoy
- Re: [Roll] [6tisch] [6lo] Proposed improvement in… Pascal Thubert (pthubert)
- Re: [Roll] [6lo] [6tisch] Proposed improvement in… Pascal Thubert (pthubert)
- Re: [Roll] [6tisch] Proposed improvement in RH3-6… Pascal Thubert (pthubert)
- Re: [Roll] [6lo] [6tisch] Proposed improvement in… Pascal Thubert (pthubert)
- Re: [Roll] [6tisch] [6lo] Proposed improvement in… Simon Duquennoy
- Re: [Roll] [6tisch] [6lo] Proposed improvement in… Michael Richardson
- Re: [Roll] [6tisch] [6lo] Proposed improvement in… Michael Richardson
- Re: [Roll] [6tisch] [6lo] Proposed improvement in… Simon Duquennoy
- Re: [Roll] [6tisch] [6lo] Proposed improvement in… Michael Richardson
- Re: [Roll] [6tisch] [6lo] Proposed improvement in… Simon Duquennoy
- Re: [Roll] [6tisch] [6lo] Proposed improvement in… Pascal Thubert (pthubert)
- Re: [Roll] [6tisch] [6lo] Proposed improvement in… Pascal Thubert (pthubert)
- Re: [Roll] [6tisch] [6lo] Proposed improvement in… Simon Duquennoy
- Re: [Roll] [6tisch] [6lo] Proposed improvement in… Pascal Thubert (pthubert)
- Re: [Roll] [6tisch] [6lo] Proposed improvement in… Simon Duquennoy
- Re: [Roll] Proposed improvement in RH3-6LoRH Pascal Thubert (pthubert)
- Re: [Roll] [6lo] [6tisch] Proposed improvement in… Ralph Droms
- Re: [Roll] [6lo] [6tisch] Proposed improvement in… Pascal Thubert (pthubert)
- Re: [Roll] [6tisch] Proposed improvement in RH3-6… S.V.R.Anand
- Re: [Roll] [6tisch] Proposed improvement in RH3-6… Pascal Thubert (pthubert)
- Re: [Roll] [6tisch] Proposed improvement in RH3-6… S.V.R.Anand