Subject: [nemo] Nemo Tree Discovery

From: "Tan, Tat Kin" <[email-masked]>
Date: Sat, 22 May 2004 16:39:59 +0800

Hello Pascal,

Would like to post some questions to you regarding to "Nested Nemo Tree
Discovery".

I very much agree with a statement at pg4 3.1 where it says "Each level
of a Nemo implies the usage of a new tunnel between the MR and its home
agent. Thus if a MNN connects to a sub-nemo which is also a sub-nemo,
packets from the MNN will be encapsulated three times." I see the
processing overheads here. :-)

When the MRs are chained in tree fashion, say, MR1 as the clusterhead
that connects to a particular AR, MR3 connects to MR2; MR4 connects to
MR3 and so on....., When a MNN that resides in, say MR6 that wish to
communicate, isnt this the same level of encapsulation and routing
overheads introduced when packets traverse via the chain, compared to
the above statement? Of cource the Tree-Balancing method could be
employed to potentially reduce the level of nested routing?

Secondly, what happen if a "branch" of the Tree is broken say, MR4 in
the chain is down? While the restructuring of Tree should be made
transparent, MNNs under MR4 and below simply would loose connections. If
such circumstance is possible, would MR5 (that connects to MR4) declare
"independent" and attempt to connect to other AR that is available and
hence form another sub-tree? How will your proposed Nemo-Tree resolved
routing potential conflicts?

What's your view on these scenarios? :) I may not be right.......

Cheers,
Tatkin

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From: "Pascal Thubert \(pthubert\)" <[email-masked]>
Date: Mon, 24 May 2004 08:10:28 +0100

Hello Tatkin

the above statement? Of course the Tree-Balancing method could be

=> You got it right, one major aspect of TD is that the tree depth is
minimized. The depth is the key both to avoid loops and to limit the
level of reencapsulation. TD is not an RO solution, rather a precursor.
Many RO techniques can be applied on top of TD, for example Reverse
Routing Header :)

=> I think this is the core of TD. MR5 maintains a conceptual ordered
Default Router List that contains all the routers that MR5 may jump to.
MR4 must have been the best from MR5 standpoint since MR5 decided to
attach to MR4. The DR List contains virtually all the routers in MR5's
line of sight but those in the same tree as MR5 but deeper. Those
unacceptable routers may be kept in a conceptually separate list, or
flagged with a state. 

=> When MR5 looses MR4 (MIP movement detection, DNA, 802.21 etc...) MR5
selects the next in the DRL and attaches to it - MRA say. In order to
save time, MR5 may have proactively allocated an address from MRA, or
may use optimistic DAD, whatever. If the DRL was empty then MR5 becomes
clusterhead of its own tree, and after some time, MR5 may reattach
deeper in the original tree since now it's a different tree. In both
cases MR5 informs attached MR of the new topology using RATIO.

=> there is more to it, see the tree hop timer and the few states that
smoothen tree migrations and merging, and the give a precise meaning to
'after some time'...

Pascal

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From: "Pascal Thubert \(pthubert\)" <[email-masked]>
Date: Mon, 24 May 2004 08:10:28 +0100

Hello Tatkin

Pascal