Re: [Roll] P2P-RPL: Data-Option in P2P-DIO

Hi Jakob,

If we agree to  remove the sequence numbers from the data option ( and, consequently, require that the Origin must not modify the data-option during a transmission ), that would be acceptable to me.

-Regards, Joseph

----- Forwarded Message -----
From: "Jakob Buron" <Jakob_Buron@sigmadesigns.com>
To: "Joseph' 'Reddy" <jreddy@ti.com>, "Mukul Goyal" <mukul@uwm.edu>
Cc: roll@ietf.org
Sent: Tuesday, May 29, 2012 8:24:03 AM
Subject: RE: P2P-RPL: Data-Option in P2P-DIO

Hi, please see my comments inline.

> -----Original Message-----
> From: roll-bounces@ietf.org [mailto:roll-bounces@ietf.org] On Behalf 
> Of Reddy, Joseph
> Sent: Friday, May 25, 2012 11:08 PM
> To: Mukul Goyal
> Cc: roll@ietf.org
> Subject: Re: [Roll] P2P-RPL: Data-Option in P2P-DIO
> 
> Hi Mukul,
> 
> See response below...
> 
> -Regards, Joseph
> 
> -----Original Message-----
> 
> [Joseph]
> Section 9.4
> Bullet 1:
> Under what conditions would a router receive the same DIO and a Data- 
> Option with higher sequence number? I assume that only the Originator 
> can include a Data-Option ? Same question also arises for section 9.5 
> ( para
> 1 )
> 
> [Mukul]
> Yes, only the origin can include a data option for delivery to the 
> target(s). In theory, the origin might have newer data to convey to 
> the
> target(s) while the route discovery is still going on. Sequence 
> numbers accounts for that possibility. Note that Data option did not 
> have a sequence number earlier (before the first LC). Then, Pascal 
> raised the possibility what if origin changes the data option. How 
> would intermediate routers and target know that this is the newer 
> data? Hence, we introduced the sequence number.
> 
> [Joseph]
> I don’t think the Origin should able to this. In fact, the Origin must 
> not make any changes to the contents of the DIO and retransmit it 
> without updating the version number. If the Origin wants to send data, 
> it should simply wait until the p2p route is setup and then use it.
> 
> The whole idea of sending UDP Data messages in the ICMP message 
> payload itself doesn’t seem quite right. It is also not simple from an 
> implementation perspective to make this kind of cross layer interactions.
> 
[Jakob]
I understand the concern about the Data Option and cross-layer interactions. I also believe that it is a sensible and necessary design choice for home automation networks. Home automation frequently requires low-latency messages to be delivered to targets for which the originator has no route. An example is a remote light switch that needs to control a relocated lamp. The fastest way to do that in a reactive routing scheme is to piggyback the data on the routing packets. The other option would be to use simple flooding, with no trickle control, which would involve generating a huge number of packets. Piggybacking data on routing packets helps avoid generating extra packets.

Home automation networks do not need to update the Data Option while a discovery is in progress. I am okay with removing the sequence numbers if they add too much complexity.

Best regards,
Jakob
> 
> 
> 
> 
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