[sugar] 65-node simple mesh test (and counting... ;-)

Bill Mccormick billmcc at nortel.com
Fri May 9 17:00:24 EDT 2008


I forgot to ask, do you have a tool that parses the messsages and counts
up etc.?   Wireshark only parses the 1st mac header.


-----Original Message-----
From: Mccormick, Bill (CAR:CTO2) 
Sent: Friday, May 09, 2008 4:31 PM
To: 'Polychronis Ypodimatopoulos'; 'Michael Stone'; 'OLPC Development'
Subject: RE: [sugar] 65-node simple mesh test (and counting... ;-)

It does look like the NM code will select APs over mesh...   I bet this
plays havoc with IP changing between link local addresses and DHCP

Did you expect over half of the packets in your data file to be
broadcasts?  Specifically 11754 out of 21587 packets were sent to the
broadcast address.


-----Original Message-----
From: devel-bounces at lists.laptop.org
[mailto:devel-bounces at lists.laptop.org] On Behalf Of Polychronis
Sent: Friday, May 09, 2008 3:35 PM
To: Michael Stone; OLPC Development
Subject: Re: [sugar] 65-node simple mesh test (and counting... ;-)

Michael Stone wrote:
> Data Questions:
> * Are the measurements used to make the display of 'distributions of
>   profile arrival rate vs. time' produced from timestamps of profile
>   arrival as recorded by all the laptops or by some smaller set of
>   'sentinels'?

All XOs got synced clocks (by means of a broadcast packet that sets the
time on all machines, providing a clock skew in the neighborhood of a
single second). Then, timestamps of profile arrivals were collected from
all 65 nodes, each reporting arrivals for the other 64 nodes.

> * What was the general nature of the connectivity graph of the 65
>   laptops? Did it change over time?

The nodes are lying in the Garden area of 1CC, and they were
consistently 1-hop away from all other nodes (full mesh network) all the

> * Did you take any measurements of background network traffic?

No, but I should have. However, we can all agree that 1CC is relatively
noisy environment.

> * Do you have any new insight into how the presence of NM (or of
>   software on top of it that depended on it) was killing your
>   interfaces?

My understanding is that the NM is trying its best to make ends meet in
terms of what the user needs (connect to an AP/XS/mesh ?) and what
connection is most "reliable" (I assume that an AP is considered more
"reliable" than the mesh, but I honestly doubt it!). As a result, the NM
may occasionally make the bold move to move from one connection type to
another, breaking all existing "connections" (quoted because there are
no TCP-like connections in my experiments), leaving stale information at
various points of the software stack (eg. mesh view).

> At any rate, thanks for this good work!
> Michael
> P.S. - When you produce measurements like these, please include links 
> to the raw data.
The raw capture is here:



Polychronis Ypodimatopoulos
Graduate student
Viral Communications
MIT Media Lab
Tel: +1 (617) 459-6058

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