Re: [Roll] Scalability of P2P-RPL

Hi,

Le 28 mars 2012 à 18:29, Mukul Goyal a écrit :

Okay, but I think that should be explicitly mentioned in the use case

As discussed today during the meeting, numbers need to be placed given a particular context.
So, if we put explicitly "4-5 hops" in the requirements, this has to be in regards to the total number of nodes, the topology, the technology used, the environment, and other numerous parameters that could justify this "4-5" value for a particular case.
For instance, if you consider 15.4 in the sub Ghz band, 15.4 in the 2.4 Ghz band or PLC technology where RPL applies, the 4-5 hops physical distance vary from at least one or two order of magnitude.
So people working over the 2.4 Ghz may use the 4-5 hops boundary, whereas people running over sub Ghz may be happy within a single hop boundary.

There is a section in the P2P draft that is quite generic, so applicable to most of the use case,  and shed some light on the tradeoff regarding using or not the P2P extension, and limit the scope of the flooding :

A network designer may take into consideration both the benefits (potentially better routes;
no need to maintain routes proactively) and costs (control messages
generated during the route discovery process) when using P2P-RPL.

We may expand this sentence to be more precise on the flooding region.

What do you think ?

I think numbers are always dangerous in documents that need to be frozen at some point.
But I agree that they are very relevant to share, when you want to leverage on other experiments.
Putting fixed numbers in protocols that target very wide scope and emerging applications is like asking to a commercial guy to put a fixed price on a product for the 20 years to come !

Just my 2 cts

Cédric.

section (or somewhere else).

Sure. I will add text to that effect. Note that the tradeoff is not straightforward: even when the P2P-RPL routes are not much shorter than routes along a global DAG, they would still avoid traffic concentration around the root.

Thanks
Mukul

----- Original Message -----
From: "Ulrich Herberg" <ulrich@herberg.name<mailto:ulrich@herberg.name>>
To: "Mukul Goyal" <mukul@uwm.edu<mailto:mukul@uwm.edu>>
Cc: "roll WG" <roll@ietf.org<mailto:roll@ietf.org>>
Sent: Wednesday, March 28, 2012 11:16:39 AM
Subject: Re: [Roll] Scalability of P2P-RPL

Mukul,

On Wed, Mar 28, 2012 at 6:09 PM, Mukul Goyal <mukul@uwm.edu<mailto:mukul@uwm.edu>> wrote:

I don't see anywhere in this section that the draft is only limited to
4-5 hops, as mentioned today. If the protocol can run in larger networks but
only for routers in maximum hop distance of 4-5, that should be spelled out
(together with a warning that TTL of the control messages has to be set to
4-5 to avoid network wide flooding).

P2P-RPL can certainly discover routes of any hop length, just that its
application would be most useful when the target is within 4-5 hops. If the
target is further out, the route along a global DAG might be almost as good.
This ofcourse depends on network topology and routing metrics in use etc.

Okay, but I think that should be explicitly mentioned in the use case
section (or somewhere else).

Regards
Ulrich
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