Subject: [lp-wan] WINDOW_SIZE and MAX_WIND_FCN

From: Shoichi Sakane <[email-masked]>
Date: Sun, 9 Dec 2018 17:22:09 +0900

Hi,

If either WINDOW_SIZE or MAX_WIND_FCN is defined, the other is settled.  So, is it enough to define one of them in a Profile ?

Below is the text.  the latest draft is same.

8.2.2.2.  Windows

   o  WINDOW_SIZE MUST be specified in a Profile.

8.4.2.  ACK-Always

   WINDOW_SIZE MUST be equal to MAX_WIND_FCN + 1.

   Each Profile, for each Rule ID value, MUST define

   o  the value of MAX_WIND_FCN

8.4.3.  ACK-on-Error

   WINDOW_SIZE MUST be equal to MAX_WIND_FCN + 1.

   Each Profile, for each Rule ID value, MUST define

   o  the value of MAX_WIND_FCN

---

From: <[email-masked]>
Date: Sun, 9 Dec 2018 15:51:53 +0000

Hello Shoichi,

Thanks for you thorough reading. Let me try to explain why we have two
parameters, even though it looks like one would be enough:
The No-ACK mode doesn't use Windows, therefore WINDOW_SIZE is not defined.
However, the FCN field is still used, if only to carry the All-1 signal to
indicate the end of the SCHC Packet.
Some LPWAN technologies want to have an FCN field wider than 1 bit, even
in No-ACK mode, to convey some information internal to their technology.
In this case, MAX_WIND_FCN is defined while WINDOW_SIZE is not defined.
It's confusing to define Windows and say that their size is MAX_WIND_FCN+1
before the FCN field and the SCHC Fragment message are defined.
It's confusing to say that the max FCN value is WINDOW_SIZE -1 when no
Windows are used.
I think it's less confusing to define the size of the windows and the max
value of FCN separately, and then link their values later in the text.
If the Group strongly objects, I'm all ears.
Best regards

Dominique

Le 09/12/18 09:22, « lp-wan on behalf of Shoichi Sakane »
<[email-masked] on behalf of [email-masked]> a écrit :

>Hi,
>
>If either WINDOW_SIZE or MAX_WIND_FCN is defined, the other is settled.
>So, is it enough to define one of them in a Profile ?
>
>_______________________________________________
>lp-wan mailing list
>[email-masked]
>https://www.ietf.org/mailman/listinfo/lp-wan

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---

From: Shoichi Sakane <[email-masked]>
Date: Mon, 10 Dec 2018 15:48:20 +0900

Hi Dominique,

Thanks for the clear explanation.

Each three mode needs MAX_WIND_FCN.  So, theoretically, if MAX_WIND_FCN is defined, WINDOW_SIZE doesn't need to define in a Profile.

How about just remove the below line from 8.2.2.2. Windows ?

It would be helpful to be consistent of a Profile.

And, MAX_WIND_FCN is something strange for me because the No-ACK mode doesn't use any windows.  I would say that simply MAX_FCN would be better.  But, it's not strong opinion.

Thanks,
Shoichi

---

From: "Carles Gomez Montenegro" <[email-masked]>
Date: Mon, 10 Dec 2018 09:05:53 +0100

Hi Shoichi,

(If I may chime in...)

> Each three mode needs MAX_WIND_FCN.  So, theoretically, if MAX_WIND_FCN is
> defined, WINDOW_SIZE doesn't need to define in a Profile.
>

Just a related comment. In appendix D, we have "WINDOW_SIZE, for modes
that use windows". Perhaps some similar text could be used in 8.2.2.2, if
we keep the two parameters.

> And, MAX_WIND_FCN is something strange for me because the No-ACK mode
> doesn't use any windows.  I would say that simply MAX_FCN would be better.
>  But, it's not strong opinion.

I agree.

MAX_WIND_FCN was introduced back in -06, when N=1 was the only possible
setting for N in No-ACK mode. At that time, MAX_WIND_FCN was defined only
for modes that used windows. Currently, as you suggest, it may be better
to just replace MAX_WIND_FCN by MAX_FCN. For window-based modes, perhaps
we may lose a bit of clarity on what MAX_FCN means, but MAX_WIND_FCN is
misleading for No-ACK...

Cheers,

Carles

---

From: <[email-masked]>
Date: Thu, 13 Dec 2018 04:21:00 +0000

Hello Shoichi,

I gave this topic a second thought, and we discussed it at the interim
meeting yesterday.
Since we don't define MAX_FCN for No-ACK mode in this draft, we don't need
this notion.
Therefore, only WINDOW_SIZE is needed.
The change is implemented and visible on GitHub
https://github.com/lp-wan/ip-compression/compare/6732a5fe74d6743a7033aeca92
65b800cea6c8db...master
Best regards

Dominique

---

From: Laurent Toutain <[email-masked]>
Date: Thu, 13 Dec 2018 07:29:56 +0100

Hi Shoichi,

>    o  WINDOW_SIZE MUST be specified in a Profile.
I will say that the WINDOW_SIZE is more a choice of the rule, it is the max
WINDOW_SIZE that can be defined in the profile for a specific technology.

for instance, if the ack are sent in frames that are 8 bytes longs, if we
take 2 bytes for the rules, 6 bytes are remaining so the max WINDOW SIZE
will be 48.

but a rule may select a FCN of 3 bits therefore the WINDOW_SIZE will be 8
(-1 bit) regarding the definiton.

Laurent