February 16, 2014
For some time now a mobile app for Andriod phones and iPhones is advertized which is called the official app of Tirol’s Avalanche Warning Service and Tiroler Tageszeitung (Tirol Daily Newspaper), so I installed it on my Android phone some days ago. Yesterday I went on a ski-tour (ski mountaineering) and on the way in the car I tried to update the daily avalanche report but it took really long and failed in the end. I thought that can’t be possible be, as the homepage of the Tyrol’s Avalanche Warning Service worked without any problems and was fast.
So when I was home again I took a closer look the traffic the app sends and receives from the Internet … as I wanted to know why it was so slow. I installed the app on my test mobile and traced the traffic it produced on my router while it launched the first time. I was a little bit shocked when I look at the size of the trace – it was 18Mbyte big. Ok this makes it quite clear why it took so long on my mobile 😉 –> So part of the post series will be getting the size of the communication down , so I opened the trace in Wireshark and took at look at it. First I checked where the traffic was coming from.
So my focus was one the 126.96.36.199 which was the IP address of tirol.lawine-app.com and it is hosted by a German provider called Hetzner (you can rent “cheap” servers there). As I opened the TCP stream I saw at once a misconfiguration. The client supports gzip but the server does not send gzipped.
Just for getting the value how much it would save without any other tuning I gzipped the trace file and I got from 18.5Mbyte to 16.8Mbyte – 10% saved. Than I extracted all downloaded files. jpg files with 11Mbyte and png files with 4,3Mbyte … so it seems that saving there will help the most. Looking at the biggest pictures leaded to the realization that the jpg images where saved in the lowest compress mode. e.g. 2014-02-10_0730_schneeabs.jpg
- 206462 Bytes: orginal image
- 194822 Bytes: gimp with 90% quality (10% saving)
- 116875 Bytes: gimp with 70% quality (40% saving)
Some questions also arose:
- Some information like the legend are always the same … why not download it only once and reuse until the legend gets update?
- Some big parts of the pictures are only text, why not sent the text and let the app render it?
- The other question is why are the jgep files 771 x 566 and the png files 410×238 showing the same map of Tirol? Downsizing would save 60% of the Size (with the same compression level)
- Why are some maps done in PNG anyway? e.g. 2014-02-10_0730_regionallevel_colour_pm.png has 134103 Bytes, saving it as jpeg in gimp with 90% quality leads to 75015 Bytes (45% saving)
So I tried to calculate the savings without minimizing the information that are transferred – just the representation and it leads to over 60% .. so instead of 18Mbyte we would only need to transfer 7Mbyte. If the default setting would be changed to 3 days instead of 7, it would go even further down, as I guess most people look only on the last 3, if even that. So it could come down to 3-4 Mbyte … that would be Ok, so please optimize your software!
I only wanted to make one post about this app, but then I found, while looking at the traffic, some security and privacy concerns I need to look into a bit closer …. so expect a part 2.