Re: [6tsch] Fwd: 6TiSCH: about join priority in IEEE802.15.4e

Hi Thomas,

when you say the "the "integer" portion of the rank in the join priority,"
you mean the result of the DAGRank(rank) function?

Cheers
Xavi

On Tue, Sep 17, 2013 at 6:59 PM, Thomas Watteyne <watteyne@eecs.berkeley.edu
> wrote:

> All,
>
> Please find below an e-mail exchange I had with Jonathan Simon, co-editor
> of the IEEE802.15.4e standard. He is confirming that driving the join
> priority field in the enhanced beacons from an upper layer does not break
> standards-compliance, which is great news.
>
> His second point is also very interesting: we could use just the "integer"
> portion of the rank in the join priority, so that the value announced is
> roughly equivalent to a hop count.
>
> Would that work?
>
> Thomas
>
> ---------- Forwarded message ----------
> From: Jonathan Simon <jsimon@linear.com>
> Date: Tue, Sep 17, 2013 at 10:14 AM
> Subject: Re: 6TiSCH: about join priority in IEEE802.15.4e
> To: Thomas Watteyne <watteyne@eecs.berkeley.edu>
>
>
> Thomas -  The join priority was intended to be used in the way you
> describe.  Note that join priority is described somewhat vaguely in the
> text - the spec does not say what to use it for other beyond a MAC
> management layer function of selecting a prospective parent, and no service
> primitives are described to set or change it.   The spec does not use the
> proscriptive "shall" or "must" language, and I certainly intended it as a
> default in absence of other upper layer methods to manage it.
>
> So as to 1), updating the join priority to reflect a node's actual
> position in the network rather than its "birth" position is a good idea.
>  WirelessHART has this capability.
> For 2),  the important thing is that all devices in the network should be
> using join priority in the same way to avoid confusion. Making the
> objective function scale in integer hops seems intuitive and simple and
> matches the default description, but if each device was n "hops" from its
> parent, it would serve the same purpose.
>
> Hope this answers your questions. Feel free to forward this to the 6TiSCH
> group.
>
> Jonathan
>  --
> Jonathan Simon, Ph. D
> Director of Systems Engineering
> Linear Technology, Dust Networks product group
> 30695 Huntwood Ave
> Hayward, CA 94544-7021
> (510) 400-2936
> (510) 489-3799 FAX
> jsimon@linear.com
>
> **LINEAR TECHNOLOGY CORPORATION**
> *****Internet Email Confidentiality Notice*****
>  This e-mail transmission, and any documents, files or previous
> e-mail messages attached to it may contain confidential information that
> is legally privileged. If you are not the intended recipient, or a
> person responsible for delivering it to the intended recipient, you are
> hereby notified that any disclosure, copying, distribution or use of any of
> the information contained in or attached to this transmission is
> STRICTLY PROHIBITED. If you have received this transmission in error,
> please immediately notify me by reply e-mail, or by telephone at (510)
> 400-2936, and destroy the original transmission and its
> attachments without reading or saving in any manner. Thank you.
>
> On Sep 12, 2013, at 12:53 PM, Thomas Watteyne wrote:
>
> Jonathan,
>
> We are discussing the interaction between IEEE802.15.4e and the RPL
> routing protocol in the 6TiSCH group (see minutes last call at [1]).
>
> We have some questions about the "Join Priority" field in the
> IEEE802.15.4e EB, in particular about how much an upper layer (6top [2])
> can influence its value. We want to make sure that we do not break
> compliance with the IEEE802.15.4e standard.
>
> For reference, this is the text in IEEE802.15.4e (p.90):
>
> The 1-octet Join Priority field can be used by a joining device to select
> among beaconing devices when multiple beacons are heard. The PAN
> coordinator’s join priority is zero. A lower value of join priority
> indicates that the device is the preferred one to connect to. The beaconing
> device’s join priority is the lowest join priority heard when it joined
> the network plus one.
>
> We have the following discussions:
>
>    1. After a node has joined, it might be moving to a different
>    topological location. In that case, it should update the Join Priority it
>    is announcing. Luckily, RPL maintains the node's rank, a concept very
>    similar to join priority.
>    *Question*: Can we have the 6top change the priority announced by
>    IEEE802.15.4e to the RPL rank (or a number calculated from the RPL rank)
>    after the node has joined?
>    2. RPL is very flexible about how rank is calculated. Depending on the
>    Objective Function used, the rank can be calculated differently. In
>    particular, the difference of the rank between a node and routing parent
>    can be different from 1.
>    *Question*: Can the join priority announced by node and its parent be
>    different by more than 1?
>
> Your input is very welcome,
>
> Thomas
>
> [1] https://bitbucket.org/6tsch/meetings/wiki/130906_webex
> [2] http://tools.ietf.org/html/draft-wang-6tsch-6top-00
>
>
>
>
> _______________________________________________
> 6tsch mailing list
> 6tsch@ietf.org
> https://www.ietf.org/mailman/listinfo/6tsch
>
>