Re: [Roll] Something to ADD

["Pascal Thubert (pthubert)" <[e-mail]>]

Hi Richard:

Note that LSRR is still workable even if the root does not store DAO
itself.

An example of that is found here:
http://tools.ietf.org/html/draft-thubert-nemo-reverse-routing-header

Note that in the RRH case, the 'multihop' DAO was carried with the
traffic as a routing header.

The reason being that the other end of the connection has to echo the
LSRR header.

Pascal

>-----Original Message-----
>From: [e-mail] [mailto:[e-mail]] On Behalf Of
Michael Richardson
>Sent: samedi 14 novembre 2009 03:44
>To: [e-mail]
>Subject: Re: [Roll] Something to ADD
>
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>
>>>>>> "Richard" == Richard Kelsey <[e-mail]> writes:
>    mcr> I guess it might be enough to have a bit that gets turned by
the
>    mcr> first non-root node that stores DAOs.
>
>    Richard> I think you need two bits.  One is turned on by the root
if
>    Richard> it stores DAOs and the other is turned on by any
>    Richard> intermediate node that stores them.
>
>  I didn't realize that the root could *not* store DAOs...!
>  I'm trying to imagine how that works.
>  I can perhaps see how this might be the case with an ungrounded DAG,
>where some random DAO-incapable node decides to become the new root.
>
>    mcr> If I understand correctly, if the intermediate nodes do not
store
>    mcr> DAOs, then they won't have a routing table to other peers, so
p2p
>    mcr> traffic will have to travel all the way up to the root and out
>    mcr> again.
>
>    Richard> Yes.  On the other hand, the DAG formation mechanism works
>    Richard> to maximize downward fanout, which in turn maximizes the
>    Richard> number of P2P routes that go through the root even if all
>    Richard> nodes store DAOs.  For example, if the root has N children
>    Richard> with roughly equal subgraphs, then each node can reach
only
>    Richard> 1/N of the network without through the root.
>
>  Yeah, I can see how a relatively uniformly distributed DAG would have
>this property.   I can also see where this would not be the case, such
>as a long linear network, such as a series of lampposts or utility
poles
>along a rural road... where the grounded node is at one of the road.
>
>    >> It seemed to me like a compromise that the root had to be able
to
>    >> create source routes so that weaker intermediate nodes could
>    >> avoid storing the DAOs. That this wasn't the ideal situation,
but
>    >> was a compromise.
>    >>
>    >> What happens if we insist all nodes store DAOs? (is it simpler?)
>
>    Richard> That uses too much RAM for us to require it.
>
>  Yes, I understand why we can not do it.
>
>  You see, I'm asking what the real tradeoff is about this.
>  If ram and CPU was free, but network bandwidth was not, would we
>decide to force all nodes to store DAOs?
>  JP has suggested that it helps.
>
>  I can see with a linear network where there is traffic up and down
the
>line, that without DAO storing nodes in the middle, traffic has to go
>all the way to the end and back.
>
>    >> What happens if we insist that no nodes store DAOs? (is it
>    >> simpler?)
>
>    Richard> Do you mean no nodes at all, or no nodes other than the
>    Richard> root?
>
>  No nodes other than the root....
>  Nothing would work if nobody knew the routes, right.
>
>    Richard> If only the root stores DAOs, then most of the P2P traffic
>    Richard> will go through the root.  As I said above, this is often
>    Richard> the case even if all node's store DAOs.  I think this
would
>    Richard> be OK.  Even without intermediate DAO storage, routing
>    Richard> packets directly to neighbors will reduce the P2P messages
>    Richard> traveling through the root.  Devices that require more
>    Richard> bandwidth (in or out) can become roots of their own DAGs,
>    Richard> as long as the number of such devices is limited.
>
>  To summarize, forbidding intermediate nodes to store DAOs:
>     - causes a loss in quality for p2p traffic for some topologies,
>       but for many topologies has a neglible effect
>     - causes no change for m2p
>     - massively reduces traffic when there is a new parent chosen
>     - simplifies the protocol (no need to record who records DAOs)
>     - removes the need for code to do different things depending
>     upon whether there are DAO storing nodes above, when changing
>     parents.
>
>  Or to be it another way, capable nodes that have the ram to store
DAOs
>are causing load on less capable nodes.   They aren't being very
>helpful.
>
>- --
>]       He who is tired of Weird Al is tired of life!           |
firewalls  [
>]   Michael Richardson, Sandelman Software Works, Ottawa, ON    |net
architect[
>] [e-mail] http://www.sandelman.ottawa.on.ca/ |device
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