Re: [lp-wan] Flow validation in ACK-on-error Mode

[Juan Carlos Zuniga <[e-mail]>]

Hi Rodrigo,

From: Rodrigo Muñoz <[e-mail]>
Sent: September 16, 2019 3:59 PM
To: Juan Carlos Zuniga <[e-mail]>
Cc: [e-mail]; Sandra Cespedes <[e-mail]>
Subject: Re: [lp-wan] Flow validation in ACK-on-error Mode

Thanks Juan Carlos for your response.

My comments below:

In your flow, you are showing a “Retransmission Timer” time between the retransmitted Reg Frag 1 and the All-1.
[Rodrigo]: Yes. This timer is definided in draft-petrov-lpwan-ipv6-schc-over-lorawan document. In the 5.5.1 said: "If this ACK is not received the end-device sends an all-0 (or an all-1) fragment with no payload to request an SCHC ACK retransmission. The periodicity between retransmission of the all-0/all-1 fragments is device/application specific and may be different for each device (not specified).

[JCZ] Ok, I thought you were referring your question to the authors of the baseline LPWAN SCHC specification (draft-ietf-lpwan-ipv6-static-context-hc), which allows several implementations for different radio technologies. The answer I gave you was with different implementation in mind (e.g. Sigfox), in which you don’t have to wait for a retransmission timer to continue transmitting your other fragments after retransmitting the missing one. If draft-petrov defines it differently I would let the authors of that draft comment (BTW, the draft has been replaced by draft-ietf-lpwan-schc-over-lorawan).


If the All-1 is the fragment that would have normally followed Reg Frag 4, there is no need for the sender to wait between retransmitting Reg Frag 4 and the All-1.
[Rodrigo]: I don't understand this. Could you explain it in more detail please? Remember that in my diagram, fragment 1 is lost, but fragments 2, 3 and 4 correctly reach the receiver. In addition, I assume that these fragments are not in the last window, therefore an All-1 SCHC message should not be sent

[JCZ] Do you mean that there are other fragments after 4 that are not depicted, or that the All-1 is transmitted alone in the last window? Perhaps explaining this would help the discussion.

This All-1 would trigger again the receiver to send a SCHC ACK, which would notify the sender of the correct (or not) reception of all the previous fragments.
[rodrigo]: Yes, I also agree with you

The problem is: what happens when the sender relays the Frag 1 message and this message is lost. Neither the sender nor the receiver have timers to start retransmissions again, or do they have them?

I corrected the diagram to give more clarity

[JCZ] Again, in the implementation that I have in mind the transmitter would send the missing fragment followed by the next not-yet-transmitted fragments in the same window. I would let Ivo et al. comment about the implementation they propose in their draft.

Best, Juan Carlos


El lun., 16 sept. 2019 a las 13:06, Juan Carlos Zuniga (<[e-mail]<mailto:[e-mail]>>) escribió:
Hello Rodrigo,

Thanks for your enquiry.

In your flow, you are showing a “Retransmission Timer” time between the retransmitted Reg Frag 1 and the All-1.

If the All-1 is the fragment that would have normally followed Reg Frag 4, there is no need for the sender to wait between retransmitting Reg Frag 4 and the All-1.

This All-1 would trigger again the receiver to send a SCHC ACK, which would notify the sender of the correct (or not) reception of all the previous fragments.

I hope this helps.

Best,

Juan Carlos

From: lp-wan <[e-mail]<mailto:[e-mail]>> On Behalf Of Rodrigo Muñoz
Sent: September 16, 2019 10:42 AM
To: [e-mail]<mailto:[e-mail]>
Cc: Sandra Cespedes <[e-mail]<mailto:[e-mail]>>
Subject: [lp-wan] Flow validation in ACK-on-error Mode

Dear Author,

I am working on the implementation of the SCHC standard for Sigfox and LoRaWAN. I have the following doubt regarding the data flow when there is a failure in the transmission of a SCHC fragment in the ACK-on-error Mode.

In this email, I attach my draft compression. Is this flow ok?

I have assumed the following:

  *   The SCHC Ack is sent immediately by the receiver at the end of the window.
Regards
--
-------------------------------------------
Rodrigo Muñoz Lara


--
-------------------------------------------
Rodrigo Muñoz Lara