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
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
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.