-----Original Message-----
From: roll-bounces at ietf.org [mailto:roll-bounces at ietf.org] On
Behalf Of JP Vasseur (jvasseur)
Sent: jeudi 19 novembre 2009 13:19
To: Richard Kelsey
Cc: roll at ietf.org
Subject: Re: [Roll] updating DAO caches (was Re: Something to ADD)
On Nov 19, 2009, at 12:01 PM, Richard Kelsey wrote:
From: JP Vasseur <jvasseur at cisco.com>
Date: Thu, 19 Nov 2009 11:36:49 +0100
On Nov 17, 2009, at 5:38 PM, Jonathan Hui wrote:
I'll have to admit that I'm not yet convinced of the benefits in
storing DAO state as it currently exists in the draft. [...]
I do agree with the first statement but not with the second
paragraph.
I do see several deployment cases where no storing DAO
would lead to
extremely sub-optimal paths and even more importantly traffic
congestion when getting closer to the root of course.
Can you share these cases with us? I agree with Jonathan
that storing
DAO states will typically not provide much improvement in
P2P routing.
Sure. I'll take the example of an inter primary+secondary
substation network (could be the smart metering network) that
supports traffic for various purposes:
meter read-out, DA alarms, ... etc. Thus traffic of various nature:
P2MP, MP2P
and P2P. There are many such networks where not storing DAO
just does not work since all P2P traffic will have to transit
via the root (unacceptable delays for
alarms) and the traffic around the root will be way too high.
This is why I am saying that having an RFC that forms a DAG
that cannot be used for outward traffic is a non-starter.
I do see several deployment cases where no storing DAO
would lead to
extremely sub-optimal paths and even more importantly traffic
congestion when getting closer to the root of course. This is true
with several networks where the amount of P2P traffic may ned up
being
not so negligible. The beauty with the current spec is
that it allows
both deployment models.
It claims to allow both, but fails to actually do so. That
is the point of the example that I gave and the reason I
keep going on about this. While the draft says that
intermediate nodes can cache DAOs, it doesn't say how those
caches are updated after a node changes parents. And
however this is done, we need to avoid the cost of sending
cache updates in the absense of any actual caches.
Yes I agree with you on this and this is why DAO packing is also
important.
Thus I would propose to all work on this and make it work
while still
allowing
some nodes to not store any DAO is they want to of course.
Does that make sense ?
Cheers.
JP.
-Richard Kelsey
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