Further studying of Abis protocols, moving towards implementation

The first quarter of 2008 is already gone, and I still haven't found all the time that I wanted to find to play with my BS11 base station[s].

However, I've spent quite a bit of time over the last couple of days further studying the GSM/3GPP 08.5x documents, as well as a thorough read through the mISDN source code.

GSM/3GPP 08.5x describe the layer1, 2 and 3 protocols of the Abis link between BSC (Base Station Controller) and BTS (Base Transceiver Station) in a GSM network. It's modelled on top of a E1 link in PCM30C configuration, i.e. TS0 is for CRC4 and synchronization, TS16 is used for the layer2+layer3 protocols, whereas the other time slots are used for transfer of the actual voice call data.

After looking at the various different driver options on Linux, I have determined that mISDN is the most promising and flexible architecture available. mISDN also has a layer0 + layer1 driver for the NT mode of the HFC-E1 card that I'm using. mISDN is great in a way that every layer is strictly separated from the other layer, and that at any layer parts of the stack can be implemented in userspace using library API.

Thus, I've started to write some mISDNuser based code to attach to the kernel-side hardware and lower-layer drivers. I'm not yet sure if the Q.921 (ISDN Layer2, also called LAPD) of the mISDN kernel side can be reused for Abis or not. The differences between standard Q.921 used on European ISDN and the Abis Layer2 are fairly small, so I hope to get it working with the existing LAPD code.

Unfortunately, I have paid work to take care of, so I will once again be distracted from this most interesting of my toy projects.

Report from FSFE FTF Licensing and Legal workshop

I'm on seven-hour train ride back from Amsterdam, where I've been attending the first Licensing and Legal workshop of the Freedom Task Force (FTF) of the Free Software Foundation Europe (FSFE).

While having a somewhat lengthy name, the FTF has been doing great work on bringing together a large group of legal and technical experts in the field of Free Software licensing. So far this was all 'virtual', happening on mailing lists.` The meeting in Amsterdam was the first of its kind, and was a huge success.

By the nature of the FSFE, most of the people were from Europe, though there were attendees from the US and even Australia, too.

There were many interesting and surprisingly interactive workshops. It was also a good opportunity to meet Armijn (the second half of gpl-violations.org) and Shane (full-time manager of the FSFE FTF), as well as many lawyers, both corporate legal counsel and from law firms.

The interest in Armijns presentation about gpl-violations.org and Till Jaeger's overview about the legal cases we've handled over the years in Germany were very well received and there was more interest and questions than the short time permitted.

What was really good for me to see is that large consumer electronics companies in Europe and the US are now implementing internal business processes to ensure GPL and other FOSS license compliance. They're also increasingly using very clear contractual language throughout their supply chain to minimize the potential risk of any "hidden" GPL surprises in products they source from OEM/ODM companies.