|------------> | From: | |------------>
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|Marek Lindner lindner_marek@yahoo.de |
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|"The list for a Better Approach To Mobile Ad-hoc Networking" b.a.t.m.a.n@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@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