[Roll] UPDATED: Moving forward with the protocol work

["Don Sturek" <[e-mail]>]

Sorry for the confusion on this...

 

When I said "in all cases" in terms of P2P support below, I meant to say
that P2P works whether the source/destination are in the same DAG and
different rank/depth or in different DAGs.  I did understand (or at least I
thought I did!) from the RPL draft that these features need to be supported
in a particular deployment instance.

 

My later note suggests the ROLL DT map some of the major requirements from
the ROLL market area requirements documents (home, urban, industrial,
building controls) to how they are addressed in the draft.  We can then have
a discussion on how well these features are addressed (not whether they are
supported!).  I think the draft is not yet clear enough on which
requirements are met and how.

 

Don

 

 

From: Don Sturek [mailto:[e-mail]] 
Sent: Thursday, July 30, 2009 10:00 AM
To: '[e-mail]'
Cc: 'Mischa Dohler'; 'ROLL WG'; '[e-mail]'
Subject: RE: [Roll] Moving forward with the protocol work

 

Hi Jerry,

 

I may have misread the RPL proposal.  I thought the Destination Address
notifications allowed the DAG root to route back down to a device in the DAG
and that feature enabled P2P in all cases.  I thought also the Destination
Address notifications for devices with lower depth/rank could be used by
devices within a DAG to more efficiently reroute P2P traffic within the DAG
(not optimally, just "more efficiently than sending the packet all the way
to the DAG root first).  I thought in all cases P2P was supported (just
without a mechanism to minimize the hop count).

 

Could someone from the DT comment on the assumptions above?

 

Did I understand that optimizing P2P for building controls is mainly about
minimizing hop counts?   If a building controls solution could choose
between optimizing hop count for P2P and flooding the network to find the
optimal P2P hop count, would it choose to flood the network?  I think it is
the lack of network flooding to establish routes and the minimal storage of
route state information along the route that I found so attractive about
RPL...


Don

 

 

From: [e-mail] [mailto:[e-mail]] 
Sent: Thursday, July 30, 2009 9:44 AM
To: [e-mail]
Cc: 'Mischa Dohler'; 'ROLL WG'; [e-mail]
Subject: RE: [Roll] Moving forward with the protocol work

 


Hi Don, 

As I read the draft, RPL doesn't currently guarantee p2p communication
regardless of hop count.  Only if some node higher in the DAG elects to
provide a path back down the DAG to the destination then there is p2p path.
RPL doesn't mandate this even for the LBR.  Hence a packet could squirt all
the way up to the LBR and still be dropped since the LBR itself has no route
defined to the destination.  You need to keep in mind that the LLN devices
are primarily a building controllers that 'moonlight' as a router; it's not
a router that happens to also do building control.  The likelihood that a
controller sitting higher in the DAG being altruist and defining pathways to
all possible sub-DAG devices is nil. 

As for hops, this is very important too.  Not so much for latency.  The time
constant for most building HVAC  control loops is in minutes so having a
packet arrive at its destination a tad late is not too concerning. (NOTE:
Fire and lighting applications are much more time critical).  The problem is
that the source device, typically a battery powered sensor must stay awake
and leave its receiver active until the packet has migrated to its
destination and the application ACK has been received.  This will reduce
battery life at least 10x.

As for scalability, a typical PAN in a commercial building is limited to a
floor which may require upwards to 250 LLN nodes.  Sure we could have
defined the PAN to be the entire complex and then require 10K nodes as do
the other requirement specs.  Empirical testing however determined that
managing 250 nodes on a single wireless domain was difficult enough with
regard to channel management, interference and hop count.  Limiting PAN size
to a floor seems to be the right balance point for complexity and
flexibility. 

Jerry 




"Don Sturek" <[e-mail]> 

07/30/2009 11:12 AM 


Please respond to
<[e-mail]>


To

<[e-mail]>, "'Mischa Dohler'" <[e-mail]> 


cc

"'ROLL WG'" <[e-mail]>, <[e-mail]> 


Subject

RE: [Roll] Moving forward with the protocol work

 

		




Hi Jerry, 
  
I think RPL does support P2P but does not optimize the number of hops. I
think that is the central issue you and Mukul are bringing up. 
  
I do question whether optimizing hops is really necessary.  I think most
applications (including building controls) can take advantage of a solution
that well supports MP2P and P2MP with extensions to provide P2P capability
(admittedly not optimized for hop count/cost but then also without nearly
the overhead of packet flooding or storage of state information that
optimized P2P solutions impose).   
  
I really don't see that trying (once again as they have in MANET for some
time) to find a single protocol that efficiently implements P2P and scales
while addressing the various data transmission patterns will result in
anything other than the same set of solutions we have today (distance vector
with flooding, link state routing and its derivatives, source routing and
its derivatives).   
  
Don 
  
  
From: [e-mail] [mailto:[e-mail]] On Behalf Of
[e-mail]
Sent: Thursday, July 30, 2009 8:58 AM
To: Mischa Dohler
Cc: ROLL WG; [e-mail]
Subject: Re: [Roll] Moving forward with the protocol work 
  


Hi Mischa, 

Nearly all communication in a commercial building facility management system
is point to point.  I'm surprised the other three requirements don't also
have a strong p2p requirement.  Back in the early 80's prior to processor
based sensors, we deployed 'dumb sensors' that would simply upload their
current environmental information to a centralized minicomputer.  This
centralized model was not scalable nor fault tolerant.  That is if the
minicomputer 'blew a gasket', the entire building went out of control. 

As soon as it was economically viable, we decentralized control by moving it
down into the rooms.  Now each room was controlled independently with an
array of room sensors and room controllers.  Now if a controller failed,
only the room might lose control, not the entire complex.  The room
controllers were then further controlled by higher level controllers.  This
distributed architecture has been in place for 25 years and is the mainstay
of building control.   

My point is that is the Commercial Market the LLN is not just a path for
moving data nortbound.  Most of the packets sent on the LLN are destined to
other nodes on the LLN.  They all require application ACKs.  About 20% of
the packets are destined to the LBR and onwards.  These are event packets
being sent to the higher layers for further analysis. 

If we don't support a robust p2p protocol option in ROLL, we will knock out
the Building Market in its entirety which means at best you will only solve
75% of the need. 


Jerry 


Mischa Dohler <[e-mail]> 
Sent by: [e-mail] 

07/29/2009 04:18 PM 

 


To

JP Vasseur <[e-mail]> 


cc

ROLL WG <[e-mail]> 


Subject

Re: [Roll] Moving forward with the protocol work


  

 

		





JP, all,

We should use this early design stage to come up with one solution - one 
solution which is not necessarily optimum for all cases but for the 
(e.g.) 95% quantile. The PHY guys learned to live with such an approach. 
The MAC folks are getting there and we should take our chance now. 95% 
means clearly to concentrate on the core issues, of which loop 
detection/avoidance, p2p and security are somehow still open.

I do understand the concept of loops arising. I have doubts that with 
the dynamics of typical ROLL networks, these will give us headaches 
within this 95% application quantile. I have read tons of papers 
produced in the last decade on routing in ROLL-type networks. Loop 
detection and avoidance was clearly not something people (including 
those doing practical rollouts and running their companies today) were 
worried about too much. Unless somebody provides me with a convincing 
study, I propose to merely adopt some simple and possibly sub-optimum 
heuristics and then forget about it.

P2P seems to worry some of us (sorry, Jerry, for having forgotten about 
the p2p paragraph). However, again, are we talking about the 95% 
quantile here? Furthermore, how much p2p exactly are you talking about? 
Any node truly to any node? Are we back to pure ad hoc then? I guess if 
IETF couldn't provide us with a magic ultra low power solution for ad 
hoc networks in past years, then chances are slim that this will work 
out now. Unless somebody provides me with a convincing study that 
adopting a general p2p ROLL protocol will not jeopardize the efficiency 
of the 95% quantile applications, I propose to adopt some simple and 
possibly sub-optimum heuristics and then forget about it.

Security is an important issue.

Now that we are at it, I sampled quite a large number of companies at an 
M2M event in Paris a few months ago organized by Orange where we met 
with JP and others. The large majority of companies present there 
explicitly told me that - for a very varying set of reasons - they would 
never let IP run over their ROLL-type networks. The sheer majority did 
suprise me. We still have a lot of work ahead.

I am in favour of adopting draft-dt-roll-rpl-01 as a WG document.

Mischa.






JP Vasseur wrote:
> Dear WG,
> 
> First of all, thanks for all the time and energy you all have devoted 
> during the past few weeks on the protocol work. There was excellent 
> followup discussion at the physical WG meeting.
> 
> To the question "Do you think that RPL provides an adequate foundation 
> for the ROLL routing protocol work", there was clearly a good consensus 
> in the WG meeting. It was also recognized there are still several open 
> issues for which we WILL need help from many WG contributors, including 
> the authors of other documents.
> 
> Could you please confirm (or not) the adoption of draft-dt-roll-rpl-01 
> as a WG document ?
> 
> Then we will of course move to the next step.
> 
> Thanks,
> 
> JP and David
> 
> 
> _______________________________________________
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