[Ns-bugs] [Bug 409] Simulation fails depending on number of wireless nodes

Mon Nov 17 15:38:28 PST 2008

http://www.nsnam.org/bugzilla/show_bug.cgi?id=409


Tom Henderson <tomh at tomh.org> changed:

           What    |Removed                     |Added
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                 CC|                            |tomh at tomh.org

--- Comment #1 from Tom Henderson <tomh at tomh.org>  2008-11-17 18:38:28 EDT ---
I was able to verify and debug the cause.  The culprit is that OLSR is
occasionally sending packets greater than 1500 bytes.  In the specific case for
40 nodes, OLSR tries to send a 1484 byte packet (which becomes 1512 bytes after
UDP and IP headers) on a 1500 byte MTU link.

The fundamental problem is that ns-3 doesn't support IP fragmentation for UDP. 
We need to decide when we are going to solve this because it will crop up
again.

For now, the workaround in OLSR to avoid this is to scale back the number of
messages that can be inserted into a single packet, such as:

--- a/src/routing/olsr/olsr-agent-impl.cc       Sun Nov 09 12:34:48 2008 +0000
+++ b/src/routing/olsr/olsr-agent-impl.cc       Mon Nov 17 15:45:42 2008 -0800
@@ -121,7 +121,7 @@

 #define OLSR_PORT_NUMBER 698
 /// Maximum number of messages per packet.
-#define OLSR_MAX_MSGS          64
+#define OLSR_MAX_MSGS          24


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