Hi Alina,
How can I utilize the iCE40 E1 USB adapter to transition from E1 to IP in a GSM network, connecting a physical Siemens BSC (which has a BTS connected) to OsmoMSC? Only the BTS and BSC are physical.
Did you say that you have only one BTS connected to your Siemens BSC?
I am not certain whether or not OsmoMSC has any support for talking to non-Osmocom BSCs: I know that Sysmocom support (for their commercial customers) the arrangement where OsmoBSC talks to pre-existing proprietary MSCs, but I don't know if there is any support for going the other way around. I am reasonably certain that OsmoMSC plus its associated OsmoMGW cannot talk to a BSC via TDM, be it osmo-e1d or otherwise - OsmoMSC+OsmoMGW combo is designed to talk 3GPP AoIP to BSCs, not the TDM version.
However, OsmoBSC plus its associated OsmoMGW instance do support the possibility of driving E1-based legacy BTS gear. Therefore, if you have only one E1-based (also Siemens?) BTS connected to your Siemens BSC, you may be able to migrate that BTS to Osmocom CNI environment by taking the legacy BSC out of the equation and making the E1-to-IP transition at the BSC (OsmoBSC+OsmoMGW) rather than at the MSC.
What are the actual models of your BTS and BSC? The specific BTS model will matter for OsmoBSC support, whereas the model of Siemens BSC is more for general education.
I also have to disclose that I have an ulterior motive in helping you with this project - I have been searching the world high and low, looking for someone who has some kind of legacy GSM BSC (at opposed to just BTS) in operation, and you may have what I've been looking for. Does your Siemens BSC include a TRAU component? If you don't know what GSM TRAU is, let me phrase the question differently: the voice channels that come out of your BSC toward the A interface (toward the MSC), what do they look like? Are they like Abis, carrying GSM-encoded speech, or are they full 64 kbit/s voice channels carrying G.711 A-law? (Either A-law or mu-law would be fine, but I am guessing A-law based on your time zone and inferred geopolitical location.)
If your Siemens BSC puts out G.711 A-law (or mu-law), then it has to include a TRAU component, and you are that precious unicorn I've been looking for! Do you have access to the management interface of that BSC, where one would presumably find an option to enable or disable TFO? Is it enabled, or can you enable it?
If your BSC is indeed TRAU-equipped and TFO-capable, I would be very happy to not only help you free-of-charge in whatever ways I can with your migration project, but possibly also pay you generously if we can work out some mechanism through which you could let me remotely play with that BSC of yours.
Sincerely, Mychaela Nadezhda Falconia (aka Nadezhda Mikhailovna in Russian) GSM/2G network operator, extreme GSM & retro-telecom enthusiast and occasional Osmocom contributor, based in USA