Re: [lp-wan] Doub about sending missing tiles

[<[e-mail]>]

Hello Rodrigo,

Thanks for your questions, they are all good!

> How do I tell the recipient which tiles I am sending in the SCHC fragment if the lost tiles are not contiguous?
A SCHC Fragment can only send contiguous tiles.

> what happens if the lost tiles are not contiguous? Should the sender send them in the same way in a single SCHC fragment?
If the lost tiles are not all contiguous, you can mix and match between the two options below

  *   Send one SCHC Fragment per missing tile (or better, per set of contiguous missing tiles)
  *   Send a SCHC Fragment with contiguous tiles that include the missing ones. Indeed, the specification does not forbid to resend tiles that have already been correctly received (we only say that the missing tiles have to be resent).

It's your implementor's freedom to choose a strategy:

  *   The simplest algorithm is to send a SCHC Fragment for each missing tile.
  *   An easy improvement to this algorithm is to try to group contiguous missing tiles into one SCHC Fragment, as much as the current MTU allows for.
  *    A more complex  algorithm is to evaluate the trade-off between sending SCHC Fragments with only missing tiles, and sending SCHC Fragments that combine missing tiles and correctly received tiles, with the goal of minimising the total overhead (I.e. tradeoff between sending SCHC headers versus resending correctly received tiles).

Your choice!

Best regards

Dominique

De : Rodrigo Muñoz Lara <[e-mail]<mailto:[e-mail]>>
Date : Friday 31 January 2020 02:27
À : Dominique Barthel <[e-mail]<mailto:[e-mail]>>
Cc : "[e-mail]<mailto:[e-mail]>" <[e-mail]<mailto:[e-mail]>>, "[e-mail]<mailto:[e-mail]>" <[e-mail]<mailto:[e-mail]>>, Sandra Cespedes <[e-mail]<mailto:[e-mail]>>
Objet : Re: [lp-wan] Doub about sending missing tiles

Hi

Thanks for your answer. Yes, that is the answer to my question.

Related to the same,  I have a new question

The draft indicates that when the sender receives a SCHC ACK with a bitmap that indicates lost tiles, the sender must send the lost tiles in a new SCHC fragment.

My question is, what happens if the lost tiles are not contiguous? Should the sender send them in the same way in a single SCHC fragment? How do I tell the recipient which tiles I am sending in the SCHC fragment if the lost tiles are not contiguous?

Thanks

El lun., 30 dic. 2019 a las 14:29, <[e-mail]<mailto:[e-mail]>> escribió:
Hello Rodrigo,

Thanks for you mail.
I'm unsure about what part of the text you actually refer to.
Section 8.3.1.2 is about the All-1 Fragment SCHC format
https://tools.ietf.org/html/draft-ietf-lpwan-ipv6-static-context-hc-24#section-8.3.1.2

From the text you quote, I think you are talking about the Sender Behavior of Ack-on-Error mode (section (8.4.3.1).
In this section, we are simply saying that the Sender must resend the missing tiles. It may use several Fragments for this.
It does not matter that the tiles are re-send packed the same way in SCHC Fragments as they were packed in the initial transmission.
Typically, if the MTU has changed to a lower value since the initial transmission, the retransmitted tiles will have to be packed in a different way (less tiles per SCHC Fragment).
Does this answer your question?
Best regards, and happy end of year

Dominique

De : lp-wan <[e-mail]<mailto:[e-mail]>> on behalf of Rodrigo Muñoz Lara <[e-mail]<mailto:[e-mail]>>
Date : Friday 27 December 2019 14:33
À : "[e-mail]<mailto:[e-mail]>" <[e-mail]<mailto:[e-mail]>>
Cc : "[e-mail]<mailto:[e-mail]>" <[e-mail]<mailto:[e-mail]>>, Sandra Cespedes <[e-mail]<mailto:[e-mail]>>
Objet : [lp-wan] Doub about sending missing tiles

Dear Author,

I have a question about draft "draft-ietf-lpwan-ipv6-static-context-hc-24". In section 8.3.1.2 say:

"On receiving a SCHC ACK, if the W field in the SCHC ACK not corresponds to the last window of the SCHC Packet:

  *

MUST send SCHC Fragment messages containing the tiles that reported missing in the SCHC ACK"

What happened if the missing tiles do not fit in a SCHC fragment?

Regards

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