CRAWDAD kyutech/interference

Measurements of HTTP requests over 802.11 in dense wireless classrooms

The common wisdom tells one not to attach more than 5-10 wireless devices to an access point.  This is a problem in wireless educational classes, one can get between 10 and 50 students in the same room.  Such spaces are referred to as dense wireless networks.   While there are several methods that can be used to deal with dense wireless environments, installing multiple APs and separating them by channel is arguably the most readily available method today.  In 802.11g/n the practical advice is to assign CH1, CH5 and CH9 to the three APs.  

However, even in such environments, wireless channels can become congested.  It was noticed that tablet terminals would often fail to complete HTTP requests or fail getting access to the wireless channel entirely.  In order to deal with this reliability problem, educational webapps had to be updated in such a way that they would detect failed requests and repeat them multiple times until a valid reply comes back. 

This dataset contains measurements which can help model such environments and the related application logic. The dataset has slightly non-trivial metrics which described failed/repeated. The experiment was run over multiple parameters and with on-the-fly changes in the layout.  The measurement itself was simple -- a web application (in browser) on user terminal would send a GET request to the web server and would download bulk of a randomly selected size. All the performance metrics were recorded at user terminals and gradually uploaded to the server -- specifically, each new request would also contain the variables containing the results of the previous request, which had negligible effect on size but facilitated efficient log-keeping. 

date/time of measurement start: 2013-03-24

date/time of measurement end: 2013-03-24

collection environment: Three 802.11 access points on channels 1, 5 and 9, with 44 tablet PCs which were moved around between experiments. A diagram can be found in the dataset.

network configuration: Three 802.11 access points on channels 1, 5 and 9.

data collection methodology: A web browser on each tablet PC would send a GET request to a web server and download a randomly selected amount of data. Performance metrics were recorded on each station and uploaded to a server.

Traceset

kyutech/interference/interference

application-layer HTTP requests over 802.11

• file: interference.tar.gz
• measurement purpose: Network Diagnosis, Educational Use

kyutech/interference Trace

• interference: application-layer HTTP requests over 802.11
• format: the file interference.csv is a CSV file with the following columns:

   time : the unix time
   uid: User ID  -- ID of the terminal in the layout PDF below
   size of request: size in kbytes
   attempts: how many times web request was sent before succeeding
   took1: the time it took for the successful request to complete, in seconds
   took2: when multiple attempts, the time from the first request until the successful reply (throughput 2 in [1])
   event: there where several changes in layout and parameters, each change is marked in the dataset (in time order)
       sync1: each terminal is supposed to send a request each 1s, size is selected randomly
       sync3: same as sync1 but for 3s interval
       sync5: same as sync1 but for 5s interval
       change: there are 3 such events marking: round1, round2 and round 3, respectively -- see the layout PDF below for the details on the respective changes