Hi Jonathan: The Backbone Router (BbR) draft makes no assumption that I am aware of on whether there is or not more than one radio hop over a LoWPAN; both cases are supported. Now I think it's fair to make a distinction between radio hops over the LowPAN and hops over the backbone:
- First, the backbone is not supposed to be of the same technology as the LoWPAN. A backbone router is thus expected to expand the 6LoWPAN compressed packets and reassemble the fragments. The backbone can a simple ethernet cable, but it might as well be a mesh of tunnels over a WAN. The packet might be delivered to an IPv6 node sitting on the backbone, or be forwarded across a destination LoWPAN via another backbone router. Because the destination LoWPAN might be different in nature from the source LoWPAN, uncompressed IP is the esperanto over the backbone. - Second, the routing protocol is somewhat different. The backbone router uses proxy ND techniques to represent its field devices over the link abstraction that is the backbone and make routing decision to forward over the LoWPAN vs. over the backbone; and the types of routing that sustains the backbone itself can be virtually anything from spanning tree to BGP. The goal for this draft is to federate multiple small LoWPANs into one larger IPv6 link over a backbone of any sort that is also part of the link. The single link requirement matches the current applications that I know of and enables a field device to move from one BrB to another one on the same link while retaining transparently its address and active connections. The backbone router is the router that enables that LoWPAN interconnection, and proxy ND is the technique that is proposed to achieve the goal above. Other techniques such as NETLMM/proxy MIP were discussed but seemed overkill for the desired result and the constraints of the LoWPAN. Pascal >-----Original Message----- >From: Jonathan Hui [mailto:[EMAIL PROTECTED] >Sent: mercredi 5 mars 2008 08:59 >To: Pascal Thubert (pthubert) >Cc: 6lowpan; [EMAIL PROTECTED]; Jay Werb >Subject: Re: [6lowpan] Compressing HC1 and HC2 into HC3 > > >In your draft, you claim that 6LoWPAN nodes address each other and the >backbone router using link-local addresses. If that occurs over multiple >radio hops, that sounds like mesh under to me... In other words, you are >assuming that an entire PAN functions as a single IP link (the IPv6 >definition of a link). Am I missing something here? > >-- >Jonathan Hui > > >Pascal Thubert (pthubert) wrote: >> Hi Jonathan: >> >> You are assuming explicitly that I am assuming implicitly... mesh >> under... Hum. >> >> Please have a look at >> http://www.ietf.org/internet-drafts/draft-thubert-lowpan-backbone-router >> -00.txt and it should be apparent that I'm not. In particular the >> backbone router is the device that will set and use the hop limit bit. >> So will all those interconnecting devices used in pseudowire, split >> bridges, IP Mobility, etc... if they are deployed in this space. >> >> What I'm really assuming is a gateway or an edge server on the link. >> It's there in most architectures that I know of at this point that's why >> I included it in the case we shoot for and saved 2 bits. Note that when >> the ULA and global addresses are used on top of link local, it makes >> sense that we define a mechanism to compress them as well. But this is >> not what HC3 is about. >> >> The goal of my initial proposal is illustrative, to foster this very >> discussion around the idea that we can shoot for a favorite case and >> make an HC3 out of HC1 and HC2 for that case. Now, if we as a group >> think that the GW assumption is not reasonable, then, fine, let us >> affect 2 bits in HC3 to indicate whether the addresses are compressed. >> >> What do the others think? >> >> Pascal >>> -----Original Message----- >>> From: Jonathan Hui [mailto:[EMAIL PROTECTED] >>> Sent: mardi 4 mars 2008 18:05 >>> To: Pascal Thubert (pthubert) >>> Cc: 6lowpan; [EMAIL PROTECTED]; Jay Werb >>> Subject: Re: [6lowpan] Compressing HC1 and HC2 into HC3 >>> >>> >>> Hi Pascal, >>> >>> Thanks for sharing your thoughts. >>> >>> By assuming the first 5 bits in HC1 are '1', you're staking a claim >> that >>> mesh-under link-local communication within a PAN is going to be most >>> common case and the one we've "shot for". If link-local is all we focus >>> on, then we are missing the point of IP. Frankly, I don't see much >>> benefit of IP if communication is limited to the PAN. >>> >>> W.r.t mesh-under, there are efforts within the IETF that assume 6LoWPAN >>> nodes will communicate via route-over using routable addresses (e.g. >>> ROLL). This brings us back to a broader topic of route-under vs. >>> mesh-under. While both will probably exist for some time, it raises the >>> question of whether 6LoWPAN implementations can support one or do they >>> have to support both. >>> >>> W.r.t compressing Hop Limit, I don't quite understand why you're using >> a >>> bit in HC3 to indicate where the message originated. If you're assuming >>> link-local communication, then messages shouldn't be forwarded across >>> links anyway. >>> >>> I do agree that there is work to do on compression and agree that there >>> are cases where HC1 and HC2 are not sufficient. This is why I've been >>> working, albeit slowly, on HC1g. >>> >>> -- >>> Jonathan Hui >>> >>> >>> Pascal Thubert (pthubert) wrote: >>>> Dear 6LoWPANers, >>>> >>>> Though HC1 and HC2 provide us with the capability to express any >>>> combination of compression, the most expected (or at least shot for) >>>> case does not lead to a better compression of the HC headers >> themselves. >>>> Seems that we could define an HC3 that would compress the pair of HC1 >>>> and HC2 for that best case. My proposal for doing this would be to: >>>> >>>> - define a new dispatch >>>> | 01 000011 | LOWPAN_HC3 - LOWPAN_HC3 compressed IPv6 and >>>> transport >>>> >>>> - define HC3 itself to: >>>> >>>> - implicitly say that the first 5 bits of HC1 are all ones >>>> - carry HC1 bits 5 and 6 (Next Header) >>>> - replace HC2 so bit 7 of HC1 is useless >>>> - provide transport specific bits such as those defined for >>>> HC-UDP, >>>> then again assuming a predefined best case if room is missing >>>> >>>> An example of what the HC3 octet could be: >>>> >>>> bits 0 1 2-3 >>>> 4-7 >>>> >>>> >> +------------------+-------------+-----------------+-------------------- >>>> ---------------------+ >>>> | reserved | reserved | Next Header | >> transport >>>> specific control bits | >>>> >>>> >> +------------------+-------------+-----------------+-------------------- >>>> ---------------------+ >>>> >>>> Next header: as defined in HC1, bits 5 and 6 >>>> >>>> transport specific control bits for UDP: >>>> bit 4 echoes HC-UDP bit 0 on UDP source port >>>> bit 5 echoes HC-UDP bit 1 on UDP destination port >>>> bit 6 echoes HC-UDP bit 2 on UDP length >>>> bit 7 is reserved >>>> >>>> What do you think? >>>> >>>> Pascal >>>> _______________________________________________ >>>> 6lowpan mailing list >>>> [email protected] >>>> https://www.ietf.org/mailman/listinfo/6lowpan _______________________________________________ 6lowpan mailing list [email protected] https://www.ietf.org/mailman/listinfo/6lowpan
