Re: [6tisch] Link Options bitmap in 6P Cell format

[Tero Kivinen <[e-mail]>]

Qin Wang writes:
> In IEEE802.15.4e, LinkOptions is defined as follows.

This was changed in the 802.15.4-2015, i.e., the MLME and he PIB no
longer specify bit numbers for those infrmation, they provide the same
information in separate parameters (TxLink, RxLink, SharedLink,
TimekeepngLink, PriorityLink), or spearate PIB entries (macTxType,
macRxType, macLinkTimekeeping and macPriorityType).

The TSCH Slotframe and Link IE do define field called Link Options and
splits it to bits as follows:

+---------+---------+-------------+-------------+----------+----------+
| Bits: 0 |     1   |      2      |      3      |     4    |   5-7    |
+---------+---------+-------------+-------------+----------+----------+
| TX Link | RX Link | Shared Link | Timekeeping | Priority | Reserved |
+---------+---------+-------------+-------------+----------+----------+
		Figure 7-54 --Link Options field format

Note, that there is new bit for Priority in there too. And as normally
this is LSB first so care should be taken when written to the IETF
draft... 

> Is it what you are going to use? Then, another way is to use two bits to
> express TX/RX/Share. I'm not sure which way is better than another.

Two bits is not enough to define all different link types. The text in
802.15.4-2015 defining the bits is:

	The TX Link field shall be set to one if it is a TX link and
	shall be set to zero otherwise.

	TX Shared links, indicated by the TX link field and Shared
	Link field both set to one, may be used by a joining device to
	send an Association Request command or higher layer message to
	the advertising device.

	The RX Link field shall be set to one if the link is an RX
	link and shall be set to zero otherwise. RX links are used by
	a joining device to receive an Association Response command or
	higher layer message from an advertising device.

	The Shared Link field shall be set to one if the link is a
	shared link and shall be set to zero otherwise. A shared link
	is one that uses contention to access the medium.

	A link may be used as both a TX shared link and RX link.

	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.

	The Priority field shall be set to one if the link is a
	priority channel access, as defined in 6.2.5.2, and shall be
	set to zero otherwise.
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