Subject: [6tisch] macLinkType for the minimal configuration (draft-ietf-6tisch-minimal-16)

From: Yasuyuki Tanaka <[email-masked]>
Date: Thu, 17 Nov 2016 16:09:10 +0100

Hi all,

I'm wondering if the cell scheduled for the minimal configuration
should be ADVERTISING in terms of macLinkType rather than NORMAL.

The definition of LinkType can be found in Table 8-46 of IEEE
802.15.4-2015. This is a table about MLME-SET-LINK.request
parameters. It says:

   Set to ADVERTISING if the link is to be used to advertise the
   network, otherwise set to NORMAL.

As we all know, the cell scheduled for the minimal configuration is
used for network advertisement; EBs are sent over the cell.

I did some research why NORNAL has been chosen for the cell, and found
the definition by IEEE 802.15.4e-2012 is a bit different to IEEE
802.15.4-2015. See Table 44f of IEEE 802.15.4e-2012, which is also a
table about MLME-SET-LINK.request parameters:

   Type of link. NORMAL = 0. ADVERTISING = 1, and indicates the link
   may be used to send an Enhanced beacon.

macLinkType has been introduced to the minimal configuration table
since draft-ietf-6tisch-minimal-01. Here is a relevant email found in
the ML archive, which was posted on June 8, 2014:

   https://mailarchive.ietf.org/arch/msg/6tisch/eF_eNIPw51UNwdv3P90qn1JMWqc

> after friday discussion it seems that having:
>
> 1) variable size slotframes and the size being announced in the EBs
> 2) 1 active cell (slotted aloha) having linkOption set at RX,TX,SHARED
> 3) The linkType for that cell can be NORMAL and it is not required to be
> ADVERTISMENT despite EBs will also be sent on that cell.
>
> I would like to ask if everybody agrees on that approach and whether not
> having a dedicated ADV cell but sending EBs in a NORMAL link is possible.

At that time, before IEEE 802.15.4-2015, it was fine to make the cell
NORMAL. I agree. But, is it still fine? Should we change the value of
macLinkType in Table 1 to ADVERTISING, or not?

Best,
Yatch

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From: Yasuyuki Tanaka <[email-masked]>
Date: Fri, 18 Nov 2016 00:59:29 +0100

Thank you for your comment, Pat!

I noticed your message wasn't on the ML; I paste it here.

On 2016/11/17 16:40, [email-masked] wrote:
>
> Yasuyuki brings up a very good point.  A major effort in creating
> 802.15.4-2015 was to eliminate (at least try to) ambiguities.  As
> per the IEEE style guide: "The word may is used to indicate a course
> of action permissible within the limits of the standard (may equals
> is permitted to ).”  The LinkType wording was modified to clarify
> when to use normal and when to use advertisement.  As per Yasuyuki
> Table 8-46 does state that "Set to ADVERTISING if the link is to be
> used to advertise the network, otherwise set to NORMAL.”  I should
> note that the text in that sub-clause adds " If LinkType is set to
> ADVERTISE, the links may be used to send Enhanced Beacon frames as
> the result of the MAC receiving a MLME-BEACON.request.”  The intent
> of 802.15.4-2015 was not meant to change the meaning of LinkType,
> rather it was meant to clarify.
>
> So, Yasuyuki’s question is indeed valid, should the minimal
> configuration set the LinkType set to Advertising?
>
> Pat
>
> Pat Kinney
> Kinney Consulting LLC
> IEEE 802.15 WG vice chair, SC chair
> ISA100 co-chair, ISA100.20 chair
> O: +1.847.960.3715
> [email-masked]

---

From: Thomas Watteyne <[email-masked]>
Date: Sun, 20 Nov 2016 18:30:57 +0100

Yatch,

Good point, indeed. The cell draft-minimal uses is indeed used for two
things: EBs and other frames. The question can we reformulate as "if we set
it to ADVERTISING, are we allowed to send non-EB frames on it" and "if we
set it to NORMAL, are we allowed to send EB frames on it".

>From the excerpts you cite, it looks like ADVERTISING makes more sense. Of
course, we are heavily in IEEE territory with this question, so we, as
6TiSCH, cannot really answer. @Pat, could you circulate this point in the
IEEE 6T IG so we can get an official recommendation on the matter from the
IEEE.

If the decision is to set the cell to "ADVERTISING", I will add an issue
and ask  the authors of draft-minimal to make the change.

Thomas

On Fri, Nov 18, 2016 at 12:59 AM, Yasuyuki Tanaka <
[email-masked]> wrote:

> _______________________________________________
> 6tisch mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/6tisch
>

-- 
_______________________________________

Thomas Watteyne, PhD
Research Scientist & Innovator, Inria
Sr Networking Design Eng, Linear Tech
Founder & co-lead, UC Berkeley OpenWSN
Co-chair, IETF 6TiSCH

www.thomaswatteyne.com
_______________________________________

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From: Xavi Vilajosana Guillen <[email-masked]>
Date: Sun, 20 Nov 2016 20:13:29 +0100

Hi, I jump in :)

We discussed this. We said to use NORMAL in order to support any type of
packet in the minimal cell/s and not only EBs. From our discussions, I
think that we all understood (at least is what I captured in the minimal
text) that if the type is NORMAL we can also send EBs there and hence we
discarded ADVERTISEMENT type.

A clarification of these will be really valuable now that I will proceed
with the revision of minimal.

regards,
X

-- 
Dr. Xavier Vilajosana Guillén
Research Professor
Wireless Networks Research Group
Internet Interdisciplinary Institute (IN3)
Universitat Oberta de Catalunya

+34 646 633 681| [email-masked] | Skype: xvilajosana
http://xvilajosana.org
http://wine.rdi.uoc.edu/

Parc Mediterrani de la Tecnologia
Av. Carl Friedrich Gauss, 5. Edifici B3
08860 Castelldefels (Barcelona)

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From: Tero Kivinen <[email-masked]>
Date: Mon, 21 Nov 2016 14:26:19 +0200

Xavi Vilajosana Guillen writes:
> packet in the minimal cell/s and not only EBs. From our discussions, I think
> that we all understood (at least is what I captured in the minimal text) that
> if the type is NORMAL we can also send EBs there and hence we discarded
> ADVERTISEMENT type. 

I would disagree with that.

Note, that LinkType of ADVERTISING and NORMAL are local matters, they
are never transmitted over air, and there is not bits for them in the
IEs.

The section 8.2.19.3 MLME-SET-LINK.request of 802.15.4-2015 says:

LinkType Enumeration ADVERTISING,	Set to ADVERTISING if the link	  
	 	     NORMAL		is to be used to advertise the	  
					network, otherwise set to NORMAL. 

And:

	If LinkType is set to ADVERTISE, the links may be used to send
	Enhanced Beacon frames as the result of the MAC receiving a
	MLME-BEACON.request.

Then in section "6.3.6 TSCH PAN formation" the text talks about the
"advertising device":

	A TSCH PAN is formed when a device, referred to as an
	advertising device, advertises the presence of the network by
	sending Enhanced Beacon frames upon receipt of a
	MLME-BEACON.request from a higher layer. In a TSCH PAN the
	Enhanced Beacon frames contain the following IEs:

...

My understanding is that the fact that LinkType is set to ADVERTISING
indicates that specific link is used to send Enhanced Beacons out,
i.e. it is used to advertise the network compared to the other tx
links, which are not used to advertise network, but which are used for
normal traffic in the network.

The ADVERTISING link can also be used to send normal traffic on it,
and it may be used to send Enhanced Beacons after the higher layer
calls MLME-BEACON.request. I.e., MAC layer somehow needs to know which
link it should be using to send beacons out, and ADVERTISING LinkType
tells that to the MAC level. I also assume that the same link is also
used to send periodic Enhanced Beacons, altough I do not think that is
specified anywhere in the 802.15.4-2015.

I do not know what the MAC level does if none of the links are set to
ADVERTISING and higher layer calls MLME-BEACON.request. It might wait
for the next ADVERTISING link, and not finding them it would not send
the EB out ever.

So I think the LinkType for the minimal should be set as ADVERTISING,
so it can will be used to send EBs and other traffic out.

> A clarification of these will be really valuable now that I will
> proceed with the revision of minimal.
-- 
[email-masked]

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From: Thomas Watteyne <[email-masked]>
Date: Mon, 21 Nov 2016 14:29:06 +0100

Tero,

Your explanation about setting the cell to ADVERTISING makes sense.

Xavi?

Thomas

On Mon, Nov 21, 2016 at 1:26 PM, Tero Kivinen <[email-masked]> wrote:

> think

Thomas Watteyne, PhD

www.thomaswatteyne.com

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From: Xavi Vilajosana Guillen <[email-masked]>
Date: Mon, 21 Nov 2016 14:45:48 +0100

yep, makes sense. We thought it in the wrong way then.

I update minimal right now.

thanks for the quick response!
X

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From: Thomas Watteyne <[email-masked]>
Date: Mon, 21 Nov 2016 14:46:25 +0100

cool, thanks

Thomas Watteyne, PhD

www.thomaswatteyne.com