Subject: [6tisch] IE TSCH Slotframe and Link. Minimal.

From: José Ángel Miranda <[email-masked]>
Date: Fri, 19 Jun 2015 13:58:43 +0200

HI,

When reading the new updated minimal, we have observed that the timekeeping
bit within the IE TSCH Slotframe and Link is not set: "...The "Timekeeping"
flag is never set, since the time source neighbor is selected using the
DODAG structure of the network..."

If you take a look to the current standard:
- Point 5.2.4.14, TSCH Slotframe and Link IE: "...RX links shall have the
Timekeeping linkOptions bit set...".
- Point 5.1.4.2a, Synchronization in a TSCH PAN: "...Note that a device
sending Enhanced Beacons to advertise a TSCH PAN should set the Timekeeping
bit in the Link Option field (as described in 5.2.4.14) for the joining
devices' receive link so that joining devices can maintain time
synchronization until additional time source neighbors are configured by a
higher layer...".

Therefore, the link within the beacon sent by the (PAN)coordinator should
be set as timekeeping too based on the current standard.

Cheers,
Jose.

---

From: Xavier Vilajosana <[email-masked]>
Date: Fri, 19 Jun 2015 17:23:58 +0200

Hi Jose,

we omitted the timekeeping flag as nodes will select time source neighbor
according to RPL parent. However you seem to be right if we want to fully
comply with the standard. In minimal we define a single slot which is
advertised by the EB, the slot is shared-tx and rx. The 15.4 standard as
you say indicates

"RX links shall have the Timekeeping linkOptions bit set."
(assuming the shall is understood as a MUST)

as for your second point. In minimal we only advertise one link which is
the same for all listening nodes. At the beginning of the network, this
link is also the RX link for all nodes joining to the advertising node. And
according to the 15.4 std, it must be set to timekeeping as you indicate.

"...Note that a device sending Enhanced Beacons to advertise a TSCH PAN
should set the Timekeeping bit in the Link Option field (as described in
5.2.4.14) for the joining devices' receive link so that joining devices can
maintain time synchronization until additional time source neighbors are
configured by a higher layer...".

we will amend the current draft with your comments.

thanks you very much!
X

2015-06-19 13:58 GMT+02:00 José Ángel Miranda <[email-masked]>:

> HI,
>
> When reading the new updated minimal, we have observed that the
> timekeeping bit within the IE TSCH Slotframe and Link is not set: "...The
> "Timekeeping" flag is never set, since the time source neighbor is selected
> using the DODAG structure of the network..."
>