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

Bill Mccormick billmcc at nortel.com
Fri May 9 15:39:30 EDT 2008

Hey Pol,

what format is the data in, is this pcap?


-----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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