Re: [6lo] working group last call (wg lc) on https://datatracker.ietf.org/doc/draft-ietf-6lo-deadline-time/

Dear Lijo and co-authors,

I went through the draft, please find my comments below:
— — 

High level comments:
*/ [GP] The draft defines the Deadline Time (DT), but it is not clear to me how the arrival of the datagram within this pre-defined DT period is guaranteed?
Indeed, the draft provides the necessary DT information, however, the only action I could observe is the delay-sensitive datagram to be dropped if the indicated DT is elapsed.

*/ [GP] I noticed that there are two different notations for LBR and 6LBR.
Shouldn’t be always 6LBR (6LBR1 and 6LBR2 when it comes to the use-cases in Section 6), instead of LBR, LBR1, LBR2 or 6LBR?

*/ “D flag (1 bit): The 'D' flag, set by the Sender, indicates the action to be taken when a 6LR detects that the deadline time has elapsed. 
If 'D' bit is 1, then the 6LR MUST drop the packet if the deadline time is elapsed. 
If 'D' bit is 0, then the 6LR MAY ignore the deadline time and forward the packet.”

[GP] It is not clear to me why the datagram should be dropped, if the 6LR detects that the DL has elapsed? 
To reduce the traffic in the network or ?

[GP] Then, the main difference in networks where this DRAFT is not considered, is that the packets are not dropped?
Because otherwise the packets are forwarded (when ‘D’ bit is 0).

Detailed comments:
*/ 5. Deadline-6LoRHE Format
“Deadline-6LoRHE encoding with 'O' flag set to 1 :

      DTL = 001, OTL = 001, TU = '10', EXP = 2, DT = 0x22B, OT = 0x22A”

[GP] What about the ‘D’ here?

*/ 6. Deadline-6LoRHE in Three Network Scenarios

[GP] Any router/device may drop the datagram (if it detects that the indicated time has elapsed), both 6LR (Relay devices) and 6LBR (DODAG Root)?

*/ 6.1. Scenario 1: Endpoints in the same DODAG (N1) in non-storing mode.
“Then 6LR begins hop-by-hop operation to forward the packet towards the 6LBR”

[GP] Then 6LR begins or “Then the 6LRs begin”? (not only one 6LR but each 6LR).
OR it should be written as in Scenario 6.3 : “Subsequently, each 6LR will perform hop-by-hop operation to forward the packet towards the 6LBR.”

*/ 6.2. Scenario 2: Endpoints in Networks with Dissimilar L2 Technologies.
“Subsequently, 6LR will perform hop- by-hop operation to forward the packet towards the 6LBR”

[GP] Subsequently, “EACH” 6LR 
OR it should be written as in Scenario 6.3 : “Subsequently, each 6LR will perform hop-by-hop operation to forward the packet towards the 6LBR.”

*/ 6.3. Scenario 3: Packet transmission across different DODAGs (N1 to N2).
“Once the packet reaches LBR2, it updates the Deadline-6LoRHE by adding the current time of DODAG2.”

[GP] is not clear to me, why “adding”, why not “subtracting”, as you mention in page 10.

[GP] Furthermore, in the example later of 6TiSCH network:
Instead of supposing an example of ASN 20050, would make sense actually to have ASN 20030, based on the topology in Figure 6, that comes with three hops.
Similarly, the rest of the math operations could be more specific, based on the topology in Figure 6.

*/ In Scenario 2:
[GP] (Optionally) DODAG 1 could be indicated/highlighted in the Figure 5 as well, as it is illustrated in Figure 6 of Scenario 3.

— — 
Best regards,
Georgios

____________________________________

Georgios Z. Papadopoulos, Ph.D.
Associate Professor, IMT Atlantique, Rennes

web: 	 www.georgiospapadopoulos.com <http://www.georgiospapadopoulos.com/>
twitter: 	@gzpapadopoulos <https://twitter.com/gzpapadopoulos?ref_src=twsrc%5Etfw&ref_url=http://georgiospapadopoulos.com/>
____________________________________

> On Apr 19, 2018, at 02:59, Gabriel Montenegro <Gabriel.Montenegro@microsoft.com> wrote:
> 
> Hi,
>  
> I just initiated a WG last call on:
>  
>               https://datatracker.ietf.org/doc/draft-ietf-6lo-deadline-time/ <https://datatracker.ietf.org/doc/draft-ietf-6lo-deadline-time/>
>  
> The WG last call will finish on Wednesday, May 2, 2018. 
>  
> Thanks in advance for your comments.
>  
> Gabriel
>  
> _______________________________________________
> 6lo mailing list
> 6lo@ietf.org <mailto:6lo@ietf.org>
> https://www.ietf.org/mailman/listinfo/6lo <https://www.ietf.org/mailman/listinfo/6lo>