Official wiki page on GSMTAP created

I've come up with GSMTAP about two years ago while working on airprobe. The goal was to have something similar to what radiotap does in the wifi world: A pseudo-header that adds additional information and context that is not present in the actual message.

Initially, GSMTAP was intended to be a separate link-layer type in the pcap file format, but this would preclude its use in real-time protocol analysis. So I modified it to be encapsulated in UDP packets, which are sent and received using normal UDP/IP sockets.

Over recent years, GSMTAP has not only been integrated into multiple programs of the airprobe project, but is also understood by wireshark. OpenBTS has also decided to adopt the format and can generate GSMTAP messages for debugging purposes.

After creating OsmocomBB, it was taught how to generate GSMTAP messages very quickly, too.

So by now, at least when it comes to Free Software, it is definitely the de-facto standard for capturing/transmitting and analyzing protocol messages from the GSM air interface.

However, until now, there has never been any official "homepage" of the GSMTAP header. This has changed now, the GSMTAP homepage is now part of the OsmocomBB wiki.

Playing more with Erlang

Last year I started to occasionally play with Erlang. People who know me as die-hard C coder who tries to avoid C++, Java and Python wherever possible will probably be surprised here now.

I have no intention of changing my general position on programming languages. I don't feel comfortable using something where I don't know and/or understand the immediate impact on how this code will be executed on the actual silicon.

However, if you have a need to play with anything that uses ASN.1, but particularly the aligned/unaligned PER encoding variants, then it is pretty clear that there is nothing available as Free Software that can compare to the Erlang asn1ct/asn1rt modules.

At that time last year I was doing some rapid prototyping with the RANAP protocol, and the progress was quite quick. I never had time to return to that project, so it (and my Erlang skills) were left dormant.

In recent weeks, I have picked Erlang up again - again to work on ASN.1 encoded messages: This time TCAP and MAP. While we still need the in-progress TCAP+MAP implementation in C for OsmoSGSN, there are other tasks at hand where an Erlang-based implementation might yield a much higher productivity.

So right now I'm working on a program that parses/decodes and iterates through every MAP component in a TCAP message and replaces certain fields, re-encodes the entire message and sends it off the wire. Once that is done, I think I'll actually try to do a more complete TCAP server and implement a simplistic HLR for OsmoSGSN testing.