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.
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
