> On Dec 10, 2015, at 7:50 AM, Pascal Thubert (pthubert) <[email protected]> > wrote: > > Hello Tero: > > Joining a tree is easy, maintaining a loopless structure is more complex. > Most of RPL complexity is actually to address the latter. We do not want to > duplicate that effort at L2. With 6TiSCH, RPL's rank is fed into the Join > Metric field. That's how we do it.
Is there an analysis published somewhere that demonstrates how time synchronization in 802.15.4-* is inadequate for 6TiSCH? - Ralph > > Cheers, > > Pascal > > >> -----Original Message----- >> From: Tero Kivinen [mailto:[email protected]] >> Sent: jeudi 10 décembre 2015 13:17 >> To: Pascal Thubert (pthubert) <[email protected]> >> Cc: Ralph Droms (rdroms) <[email protected]>; [email protected]; draft-ietf- >> [email protected] >> Subject: Re: [6tisch] #40 (minimal): Ralph's INT AREA review on minimal >> >> Pascal Thubert (pthubert) writes: >>>> That capability is part of our bare minimum. If someone only cares >>>> for hub and spoke, then RPL is not needed, but supporting only that >>>> model is below the bar of the 6TiSCH bare minimum. >>>> >>>> I still think tying the join process to the use of RPL is a bad >>>> idea, but that's a minor design point for the WG. >>> >>> If it was only that, I'd agree. >>> >>> But we also need RPL to build a loop-less structure for the clock >>> synchronization, so we do not need an additional routing method for >>> that purpose only. >> >> Hmm.. why do not use the 802.15.4 way of doing that? 802.15.4 already has >> method of generating time synchronization hierarchy. >> >> I.e. the 802.15.4 says that Join Metric (used to be Join Priority) is set to >> be the >> received EB Join Metric + 1. >> >> From the 802.15.4e: >> >> The beaconing device’s join priority is the lowest join >> priority heard when it joined the network plus one. >> >> From the 802.15.4-2015: >> >> The sum of one and the value of the Join Metric field from the >> TSCH Synchronization IE, 7.4.4.2, received in the Enhanced >> Beacon frame used by the device joining the network. If the >> device is the an endpoint, the value shall be set to zero. >> >> So in the 802.15.4 the join metric of PAN coordinator / endpoint is 0, all >> nodes >> joining directly to it has join metric of 1, and nodes joining to them has 2 >> and so >> on. >> >> If the 6TiSCH is using join Metric differently then it will not be following >> the >> 802.15.4. >> >>> As you know, clock synchronization is key to the TSCH operation and if >>> a node loses its sense of time, it lose connectivity and will need to >>> rejoin. >> >> Which is why it is already specified in the 802.15.4. See section >> 6.5.3 Synchronization in TSCH PAN of the 802.15.4-2015 (used to be section >> 5.1.4.2a in 802.15.4e). >> -- >> [email protected] _______________________________________________ 6tisch mailing list [email protected] https://www.ietf.org/mailman/listinfo/6tisch
