OpenBSC on its way to get funded A-interface development

There is more commercial interest in OpenBSC than I expected initially when I started the project as a 'just for fun playground for GSM hacking'. Now we have received an inquiry from a company who wants to fund the development of an actual A interface to OpenBSC. This basically means that somebody wants to hook up OpenBSC to an actual real-world MSC (Mobile Switching Center) of an actual real-world GSM network.

The A interface is the interface between the BSS (BSC + BTS) and the higher levels of the telephony network. The interface is based on SS7 and lives on top of SCCP. There's BSSMAP, DTAP and OMAP. Both connection-less and connection- oriented modes of SCCP are required.

What this means is that OpenBSC's software architecture will shift even further towards the traditional GSM network architecture. So far, we have a "full GSM network from BSC to MSC/HLR in a box" approach. This makes it easy to implement, but is quite restrictive. You cannot route/switch calls to a different network, e.g.

The recent patches posted by Andreas Eversberg already introduce a software interface called mncc into the OpenBSC codebase. While those patches are not merged yet, they are introducing a functional split between the call-control entity on one hand, and the RR and NM as well as Abis RSL/OML functionality on the other side.

When we introduce the A interface, the functional split in the software will be driven even further. We'll first introduce an API at the traditional BSC/MSC split, and then write a BSSMAP/DTAP/OMAP protocol interface to that API.

One thing is for sure: We'll always keep the 'run everything in one box' mode around. This is still the most useful case for small-scale experimentation with GSM.

I'm definitely looking forward to see this project grow. We still have no agenda for things like GPRS/EDGE support, or any kind of handover. But then, development one step at a time is more healthy than trying to do everything at the same time.

I'm really excited to play with the A interface, and to interact with an actual MSC on a protocol level. This sort-of completes my ventures into GSM protocol land, from the Um (on-air) over A-bis to the A interface, one iteration up the network hierarchy at a time.