[6tisch] Benjamin Kaduk's Discuss on draft-ietf-6tisch-architecture-24: (with DISCUSS and COMMENT)

[Tero Kivinen <[e-mail]>]

Benjamin Kaduk via Datatracker writes:
> ----------------------------------------------------------------------
> DISCUSS:
> ----------------------------------------------------------------------
> 
> Section 4.3.4 asserts:
> 
>    [...]                                      We'll note that the Join
>    Priority is now specified between 0 and 0x3F leaving 2 bits in the
>    octet unused in the IEEE Std. 802.15.4e specification.  After
>    consultation with IEEE authors, it was asserted that 6TiSCH can make
>    a full use of the octet to carry an integer value up to 0xFF.
> 
> I'm extremely reluctant to publish this text in the IETF stream without
> a citation.

IEEE Std 802.15.4-2015 says:

----------------------------------------------------------------------
7.4.4.2 TSCH Synchronization IE

The TSCH Synchronization IE Content field shall be formatted as
illustrated in Figure 7-50.

          +-------------+---------------+
	  |  Octets: 5  |       1       |
          +-------------+---------------+
	  |     ASN     |  Join Metric  |
          +-------------+---------------+

     Figure 7-50 -- TSCH Synchronization IE Content field format
	   
The ASN field contains the ASN corresponding to the timeslot in which
the enhanced beacon is sent. The ASN is used as the Frame Counter for
security operations if enabled.

The Join Metric field is an unsigned integer and shall be set to
macJoinMetric.
----------------------------------------------------------------------

And

----------------------------------------------------------------------

Section 8.4.2.2 TSCH-specific MAC PIB attributes

...

       Table 8-83 -- TSCH-specific MAC PIB attributes

Attribute	Type     Range       Description                     Default
...
macJoinMetric	Integer	 0x00–0xff   The sum of one and the	     1
			 	     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 it is very clear that Join Metric can be any number between
0x00-0xff. 

>    scheduled cell:  A cell which is assigned a neighbor MAC address
>                (broadcast address is also possible), and one or more of
>                the following flags: TX, RX, shared, timeskeeping.  A
> 
> "timeskeeping" does not seem to be defined anywhere.

Timekeeping comes from the IEEE Std 802.15.4-2015 Section 7.4.4.3 TSCH
Slotframe and Link IE:

----------------------------------------------------------------------
   The Timekeeping field shall be set to one if the link is to be used
   for clock synchronization and shall be set to zero otherwise. RX
   links shall have the Timekeeping field set to one.
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