10 Aug
2009
10 Aug
'09
7:57 a.m.
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| From: |
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|Marek Lindner <lindner_marek(a)yahoo.de>
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| To: |
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|"The list for a Better Approach To Mobile Ad-hoc Networking"
<b.a.t.m.a.n(a)lists.open-mesh.net>
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| Date: |
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|10.08.2009 09:50
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| Subject: |
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|Re: [B.A.T.M.A.N.] batman goes looping...
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| Sent by: |
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|b.a.t.m.a.n-bounces(a)lists.open-mesh.net
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On Monday 10 August 2009 15:20:28 Yang Su wrote:
For the echo cancellation example: the problem happens
with the
interaction
between A and B. Because of the asym link, A chooses B
as its next
neighbor
towards F. Because the asym path is short, B always
receives F's OGM from
A
first (before B receives the OGM with the same seqno
from C). As a
result,
from A's point of view, F's OGMs rebroadcasted
by B are always echoes and
A
will never update the TQ information towards F via B.
When the quality of any links on the path B to F drops down, B might
choose
A as its next neighbor towards F and a loop forms
between A and B.
Ah, here we have the misunderstanding. Let me briefly outline how the echo
cancellation works (I refer to your PDF-example):
1. Node C emits a packet.
2. Node B receives it and writes the address of Node C in the previous
sender
field because it received that packet via C. Now, B rebroadcasts the OGM.
-- B has already rebroadcasted an earlier OGM with the same sequence number
(received from A). Will B rebroadcast the OGM with the same sequence number
(received from C) again?
3. Node C receives the packet it sent before and discards it as the packet
contains its own address in the previous sender field.
4. Node A happily receives the packet (and goes back to step 2).
Cheers,
Yang