Gory details of USIM authentication sequence numbers

I always though I understood UMTS AKA (authentication and key agreement), including the re-synchronization procedure. It's been years since I wrote tools like osmo-sim-auth which you can use to perform UMTS AKA with a SIM card inserted into a PC reader, i.e. simulate what happens between the AUC (authentication center) in a network and the USIM card.

However, it is only now as the sysmocom team works on 3G support of the dedicated OsmoHLR (outside of OsmoNITB!), that I seem to understand all the nasty little details.

I always thought for re-synchronization it is sufficient to simply increment the SQN (sequence number). It turns out, it isn't as...

GTA04 project halts GTA04A5 due to OMAP3 PoP soldering issues

For those of you who don't know what the tinkerphones/OpenPhoenux GTA04 is: It is a 'professional hobbyist' hardware project (with at least public schematics, even if not open hardware in the sense that editable schematics and PCB design files are published) creating updated mainboards that can be used to upgrade Openmoko phones. They fit into the same enclosure and can use the same display/speaker/microphone.

What the GTA04 guys have been doing for many years is close to a miracle anyway: Trying to build a modern-day smartphone in low quantities, using off-the-shelf components available in those low quantities, and without a large company with its associated financial backing.

Smartphones...

Diodes part 3: a working diode steering circuit

I've made something interesting with my aluminium and soda bicarb diodes: a 7-segment display encoder. Also includes instructions on how to make your own.

Kalman filter

In few projects I've needed the Kalman filter to suppress the noise and other inaccuracies especially from accelerometers. Below is a nice picture from a live stream of data transmitted by the ESP8266 LDR over websockets to an application server written in javascript. The data received in the browser looks like:
With red is raw data and with white is the predicted data after the Kalman filter was applied.

Inside of a 1000lx bulb LED

Since this Livarno bulb refused to work after few months of fine operation I decided to dismount it.
Power supply was covered in rubber and it take a while to clean it between the components.
32 LEDs are used for this bulb. I've tested few of them with a 5V power supply and are very bright (don't look at them since is not a nice feeling after that)
Here is the power supply. Still has rubber left between components.

Manual testing of Linux Kernel GTP module

In May 2016 we got the GTP-U tunnel encapsulation/decapsulation module developed by Pablo Neira, Andreas Schultz and myself merged into the 4.8.0 mainline kernel.

During the second half of 2016, the code basically stayed untouched. In early 2017, several patch series of (at least) three authors have been published on the netdev mailing list for review and merge.

This poses the very valid question on how do we test those (sometimes quite intrusive) changes. Setting up a complete cellular network with either GPRS/EGPRS or even UMTS/HSPA is possible using OsmoSGSN and related Osmocom components. But it's of course a luxury that not many Linux kernel networking hackers...

Cellular re-broadcast over satellite

I've recently attended a seminar that (among other topics) also covered RF interference hunting. The speaker was talking about various real-world cases of RF interference and illustrating them in detail.

Of course everyone who has any interest in RF or cellular will know about fundamental issues of radio frequency interference. To the biggest part, you have

cells of the same operator interfering with each other due to too frequent frequency re-use, adjacent channel interference, etc.

cells of different operators interfering with each other due to intermodulation products and the like

cells interfering with cable TV, terrestrial TV

DECT interfering with cells

cells or microwave links interfering with SAT-TV reception

all types...

Towards a real SIGTRAN/SS7 stack in libosmo-sigtran

In the good old days ever since the late 1980ies - and a surprising amount even still today - telecom signaling traffic is still carried over circuit-switched SS7 with its TDM lines as physical layer, and not an IP/Ethernet based transport.

When Holger first created OsmoBSC, the BSC-only version of OpenBSC some 7-8 years ago, he needed to implement a minimal subset of SCCP wrapped in TCP called SCCP Lite. This was due to the simple fact that the MSC to which it should operate implemented this non-standard protocol stacking that was developed + deployed before the IETF SIGTRAN WG specified M3UA or SUA came around. But...

Testing (not only) telecom protocols

When implementing any kind of communication protocol, one always dreams of some existing test suite that one can simply run against the implementation to check if it performs correct in at least those use cases that matter to the given application.

Of course in the real world, there rarely are protocols where this is true. If test specifications exist at all, they are often just very abstract texts for human consumption that you as the reader should implement yourself.

For some (by far not all) of the protocols found in cellular networks, every so often I have seen some formal/abstract machine-parseable test specifications. Sometimes it was TTCN-2, and...

FOSDEM 2017

Last weekend I had the pleasure of attending FOSDEM 2017. For many years, it is probably the most exciting event exclusively on Free Software to attend every year.

My personal highlights (next to meeting plenty of old and new friends) in terms of the talks were:

20 Years of Linux Virtual Memory by MM-Guru Andrea Arcangeli

GPU-Enabled Polyphase Filterbanks by Jan Kraemer

Virtual multi-antenna arrays for estimating the bearing of radio transmitters by Francois Quitin

Secure Microkernel for Deeply Embedded Devices by Jim "jserv" Huang

A discussion of Fedora's Legal state by Tom Callaway

Radio Lockdown Directive by Max Mehl

I was attending but not so excited by Georg...