Exploring the Motorola Horizon macro BTS

Some days ago, my new 100kg toys have arrived: The Motorola horizonmacro indoor cabinets, populated with 3 GSM 1800 TRX each. Pictures are at the openbsc.osmocom.org wiki

It took some time to manufacture the power cable, and specifically the E1 cable (where I had to reverse engineer the pin-out of a 37pin sub-d connector that the so-called BIB (balanced interface boards) use.

The next biggest time consumer was the fact that the command line based user interface (MMI) has three modes; MMI-ROM, MMI-RAM and emon. Figuring out which commands to use to switch modes isn't really something that you can easily find. Especially the fact that the MMI-ROM to MMI-RAM switching command has a parameter that needs to be identical with one stored on the PCMCIA flash card (number "18" in my case), didn't make things any easier.

So as an intermediate summary, I can make the following comments about the Motorola BTS and specifically A-bis architecture:

  • Motorola seems more proprietary and less specification oriented than what I've seen so far (Ericsson, ip.access, Siemens, Nokia).
  • They do not seem to implement a SAPI=62 OML link on A-bis at all
  • Thus, there is no GSM TS 12.21 compatible OML protocol at all
  • Instead of using individual OML messages and/or attributes to set things like ARFCN, BSIC and the like, the Motorola BSC seems to generate one big database blob containing all parameters. This blob is downloaded into the BTS RAM (optionally its PCMCIA Series2 flash card).

Particularly the latter part is causing quite some problems for me. As I don't have a Motorola BSC, I cannot generate those database files. My BTS units come with databases on their PCMCIA flash cards. I can view their contents on the MMI. However, their config (EGSM) doesn't match the actual radio hardware that's installed. Even after hours spent with the MMI, there seems absolutely no way how those parameters can be altered locally

I also have not found any hint / documentation at all about something like a LMT (local maintenance terminal) like other BTS vendor. Using such a software on a PC, you can typically configure the BTS via a RS232 line.

So most of my hope now lies in being able to analyze dumps of those old Series2 flash cards in order to get some hints on that database format.

If anyone has any of the following information, it would make my day:

  • Motorola A-bis / Mo-bis protocol traces
  • Any Motorola BTS config databases (independent of BTS model/version)
  • The sample database files that come with a Racal 6113 Option 225
  • Any information on the database format
But to be honest, I don't have much hope. The equipment is old (about 1999), and only very few operators have been using it, as it seems.