08 July 2010


I returned from the Pfarrkirchen OpenBTS workshop just over week ago and am finally sitting down to write about it. I hope everyone enjoyed themselves and learned a lot, which certainly appeared to be the case. Dieter Spaar offered his farm for event and made excellent preparations. If you want to see some photos, Ali Gündüz posted some good ones on his blog. We also discovered a new way to test the robustness of our mechanical packaging: Check a BTS unit onto United Airlines and see what's left of it when you get it back. Their baggage handlers managed to slam one of our cases against the ground so hard that they broke the rack-mounting tabs on our Elma 2U boxes and even damaged the internal elements of a cavity filter.

The general form of the workshop was to divide the class into small teams and assign each team a "pet" OpenBTS unit to configure and hack over the next three days. The material was broken into topic-oriented sessions, starting with an overview of the physical layer and ending with a multi-BTS network carrying phone calls and text messages. The presentation style was usually 30-45 minutes of theory followed by a live demonstration or class exercise on each team's BTS. The operating area of the network was a little smaller than hoped, mostly due to mud, but there's not much than can be done to control the weather and I think everyone was understanding about that.

(Workshop class session: SMS handling. Thanks to Mark P. for this photo.)

(We ate a hearty Bavarian menu, catered to the farm. Thanks to Mark P. for this photo.)

One of the things I appreciated most about this workshop was the collection of attendees. They came from a range of backgrounds: network operators, academics, development specialists, security specialists -- a very broad mix. Together, this group produced some really great discussions during the breaks and meals. I felt very fortunate to have met them all in person and in one place. Plus, Harald Welte and Karsten Nohl came out to the farm as well to participate in the discussions and present some short demos of OpenBSC and OsmocomBB. Harald even (unintentionally) fuzzed our systems with malformed messages from one of his test phones, something that I now plan to make part of our regular testing.

(Downlink signal strength from the BTS unit used by Ali's team. See his blog for a photo of the actual unit. Thanks to Dieter for taking these measurements and making this map.)