Hi Polychronis, Thanks for sharing the results. Did you use a wireless AP or active antenna? If you can include a few details on that it will help. Can you also include the XO build # and XS build and config if relevant?
Would you say that this test passed? That is, can we recommend that schools use the chat activity with one chat session which all join? Lastly, can you tell us what kind of testing time and focus you will have in the near future? I believe there is a mesh test lab coming up at Nortel in Ottawa as well. Any feedback on test capacity and plans there is appreciated too. I ask because there is recent feedback on mesh issues from a teacher at Lambayeque, Peru http://wiki.laptop.org/go/Lambayeque#Inconvenientes and a teacher in Uruguay has asked about supported Mesh features too. The Lambayeque page says: they wish they knew in advance that Acoustic Measure Activity would not work with 6 groups of two students each. That's mostly an issue with activity design and our communication about what activities support but it does raise a good test case (6 groups of 2 sharing a single activity). I think both (Peru and Uruguay) teachers can help define meaningful mesh use cases which will be applicable in many schools. I want to set the right expectation on our capacity before I ask them to spend a lot of time working with us. I can start by telling them that chat as you describe above will work well, if you agree. Then we can follow up to gather more details on how they want to use the mesh. The good news is they are motivated to use the mesh which helps validate one design goal of the XO. Now we just need to understand how they want to use it :-) It looks like you are focused on finding the maximum scale of Xos which can be in a mesh. That's clearly important info too. I'm just checking if you have capacity to look at a few other test scenarios as well. Thanks, Greg S **************************** Message: 5 Date: Fri, 09 May 2008 03:29:51 -0400 From: Polychronis Ypodimatopoulos <[EMAIL PROTECTED]> Subject: 65-node simple mesh test (and counting... ;-) To: OLPC Development <[email protected]>, Sugar ml <[EMAIL PROTECTED]>, [EMAIL PROTECTED] Message-ID: <[EMAIL PROTECTED]> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Dear devel, Here are the latest results from Cerebro's (http://cerebro.mit.edu) scaling properties. A 65-node testbed was used (703, Q2D14). The NetworkManager had to be disabled in order to stabilize the behavior of each XO's wireless interface. Unfortunately, the difficulty and time necessary to manage increasingly more nodes is linear (given that the NetoworkManager is disabled ;-), but increases steeply. ** Test plan: Cerebro was started on all 65 laptops almost at the same time. We attempted to emulate the "65 children turn on their laptops in class at the same time" scenario. With Yani's help, it took about 5 seconds for both of us to press 'enter' on all laptops. Each XO would discover each other, exchange profile information and keep exchanging presence/discovery information. ** Measurements: Quantitative: According to the protocol, presence (mac address) arrives about other XOs first, then the profile for the newly arrived mac address is queried and finally the profile is cached. We assume that initially each XO has no cached information about other XOs. As a result, every XO will query everyone else. We measured the time it took for each XO to discover and exchange profile information with everyone else, bandwidth usage at all times (during profile exchange and after the network stabilized when all profiles were received everywhere) Qualitative: Collaboration was tested on all 65 nodes: one shared a chat session, everyone else joined. The chat session was based on Cerebro's collaboration model. ** Results: Discovery and profile information: The following graph shows arrival of profile information at each XO from other XOs a function of time. Each bar is a 3-second bucket representing the average number of profile arrivals during this 3-second period. The standard deviation is shown with the blue lines. http://wiki.laptop.org/images/a/af/65-arr-1.png The following graph is the cumulative distribution function. It shows that, on average, each XO has received about 95% of the profiles of the rest of the nodes within just 20 seconds. This performance boost is due to the fact that each XO queried for its profile, responds by broadcasting the profile, instead of unicasting it to the requester. As a result, the other nodes receive the profile too and the next node is queried, yielding a linear cost, instead of a quadratic one. http://wiki.laptop.org/images/7/72/65-cdf-1.png Bandwidth usage: The following wireshark snapshot shows bandwidth usage that peaks momentarily at about 60kbytes/sec. The snapshot is also in accordance with the first graph above, showing that after about 55 seconds the network stabilizes. After the network stabilizes, bandwidth usage drops to 1 packet every 3 seconds (less than 500bytes/sec), as the arrival rate adapts to the density of the network. http://wiki.laptop.org/images/5/51/Bandwidth-presence-info-1.png Chat session: Before the experiment was started, a node shared a chat session and all 64 nodes joined consistently. I sent a few chat messages from a couple of XOs and were received on all other XOs. ** Other notes After about 6.4 hours of continuous operation on all 65 nodes, Cerebro shows stable memory usage (<10MB) and consistent CPU usage (83 minutes of CPU usage in 'top'). Comments/suggestions? Pol -- Polychronis Ypodimatopoulos Graduate student Viral Communications MIT Media Lab Tel: +1 (617) 459-6058 http://www.mit.edu/~ypod/ _______________________________________________ Devel mailing list [email protected] http://lists.laptop.org/listinfo/devel
