The reason we see icons flashing here and there in the mesh view.. i.e. "xmas tree effect"

Sjoerd Simons sjoerd at
Fri Dec 14 04:31:55 EST 2007

On Thu, Dec 13, 2007 at 11:18:01PM -0500, Giannis Galanis wrote:
> 6 XOs connected to channel 11, with forwarding tables blinded only to them
> selves, so no other element in the mesh can interfere.
> The cache list was scanned continuously on all XOs using a script
> If  all XOs remained idle, they all showed reliably to each other mesh view.
> Every 5-10 mins an XO showed as dead in some other XOs scns, but this was
> shortly recovered, and there was no visual effect in the mesh view.

Could you provide a packet trace of one of these XO's in this test? (Install
tcpdump and run ``tcpdump -i msh0 -n -s 1500 -w <some filename>''.

I'm surprised that with only 6 laptops you hit this case so often. Ofcourse the
RF environment in the OLPC is quite crowded, which could trigger this.

Can you also run:
Run it as ``python server'' on one machine and just ``python'' on the others. This should give you an indication of the amount of
multicast packet loss.. Which can help me to recreate a comparable setting
here by using netem.

> If you switched an XO manually to another channel, again it showed "dead" in
> all others. If you reconnected to channel 11, there is again no effect in
> the mesh view.
> If you never reconnected, in about 10-15 minutes the entry is deleted, and
> the corresponding XO icon dissapeared from the view.
> Therefore, it is common and expected for XOs to show as "dead" in the Avahi
> cache for some time for some time.
> IF a new XO appears(a message is received through Avahi),
> WHILE there are 1 or more XOs in the cache that are reported as "dead"
> THEN Avahi "crashes" temporarily and the cache CLEARS.
> At this point ALL XOs that are listed as dead instantly disappear from the
> mesh view.

Interesting. Could you file an trac bug with this info, with me cc'd ?

Everything should be made as simple as possible, but not simpler.
		-- Albert Einstein

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