Re: [6tsch] set DAGRank to Join Priority

Xavi,

Let's take the example in your draft to see what the problem is. Please
point out if I'm wrong.
+-------+
     |   0   | R(0)=0
     |       | DAGRank(R(0)) = 0
     +-------+
         |
         |
     +-------+
     |   1   | R(1)=R(0)+683=683
     |       | DAGRank(R(1)) = 2
     +-------+
         |
         |
     +-------+
     |   2   | R(2)=R(1)+683=1366
     |       | DAGRank(R(2)) = 5
     +-------+
         |
         |
     +-------+
     |   3   | R(3)=R(2)+683=2049
     |       | DAGRank(R(3)) = 8
     +-------+
         |
         |
     +-------+
     |   4   | R(4)=R(3)+683=2732
     |       | DAGRank(R(4)) = 10
     +-------+
         |
         |
     +-------+
     |   5   | R(5)=R(4)+683=3415
     |       | DAGRank(R(5)) = 13
     +-------+

>From the example, you can see R(n) is a 2-byte integer, and DAGRank is
always the higher byte of the 2byte integer, because minHopRankIncrease =
256.

If set JoinPriority = DAGRank, then it is possible JoinPriority> 0x3f
(although it unlikely happens often), out of its range.
If set JoinPriority[5:0] = DAGRank[7:2], (Is it your suggestion?), a new
node may found many existing nodes with same JoinPriority in received EB.
In another word, the JoinPriority can not provide information about
preferring joining. Right?

I haven't had good solution for it. So, I hope the range 0x00~0x3f is not a
"MUST" in IEEE802.15.4e.

What  do you think?
Qin

On Sat, Sep 28, 2013 at 2:30 AM, Xavier Vilajosana Guillen <
xvilajosana@eecs.berkeley.edu> wrote:

> Hi Qin,
>
> after thinking a little bit on that maybe we can use the higher byte of
> the rank for that. that is  rank>>8, the higher byte is a monotonically
> increasing counter. As each hop is <<8 (due to minhopRankIncrease) we can
> have the sense of higher join priority as higher the rank.
>
> In addition having if we have the limitation of 0x3F, this means that we
> will support Join priorities up to 0x3F that translated to ranks are
> 0x3F<<8 (big number) ..
>
> just thoughts...
> X
>
>
> On Fri, Sep 27, 2013 at 10:30 AM, Qin Wang <qinwang@berkeley.edu> wrote:
>
>> Hi Thomas,
>>
>> I think with OF0 the DAGRank is uint8. But, in the Table 52b of
>> IEEE802.15.4e, the range of Join Priority is 0x00~0x3f. If the range is a
>> "MUST", we have to have a function mapping a DAGRank in 0x00~0xff to a
>> JoinPriority in 0x00~0x3f. Correct?
>>
>> Would you please confirm with some expertise in IEEE802.15.4e if the
>> range 0x00~0x3f is a MUST or not?
>>
>> Thanks
>> Qin
>>
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>