OsmoBSC doesn't handle RESET IP RESOURCE BSSMAP message
According to TS 148 008 section 18.104.22.168.2 Reset IP Resource procedure initiated by the MSC:
On reception of this message the BSS shall release locally the resources and references associated to the specific Call Identifiers indicated in the received message. The BSS shall always return the RESET IP RESOURCE ACKNOWLEDGE message to the MSC after all Call Identifier related resources and references have been released and the BSS shall include the list of Call Identifiers. The list of Call Identifiers within the RESET IP RESOURCE ACKNOWLEDGE message shall be in the same order as received in the RESET IP RESOURCE message. Unknown Call Identifiers shall be reported as released.
Right now OsmoBSC doesn't handle this message and thus doesn't send RESET IP RESOURCE ACKNOWLEDGE to MSC, which looks like a violation of the standard.
In the attached trace you could see that MSC sends RESET IP RESOURCE right after the connection RESET because the BSC was power cycled during active operation. After OsmoBSC doesn't respond, the MSC retires twice and gives up.
At the minimum, it would be great to respond to at least those RESET IP RESOURCE messages for which we don't have known calls - this would cover the case above with a restarted OsmoBSC. We might want to blindly send DLCX to OsmoMGW in this case, to make sure it releases the relevant endpoints. Though I'm not sure this is a reliable way to reset stale OsmoMGW endpoints after an OsmoBSC crash.