Osmocom Libraries » libosmo-sccp + libosmo-sigtran

There are implementations out there which send us traffic, specifically in this case SCMG (SST) that has only SSN in both Called and Calling Party. This means the inbound SST message is routed correctly to the local SCCP user of libosmo-sigtran. But when that user respons with inverting Called/Calling Party, the new destination again just contains a SSN.

As a result, we don't know where to route the message (we always need a PC).

1. implement a "pure ASP" mode that assumes we only have one AS, no MTP-level routing and hence we can send all traffic to any active ASP within that single AS, or
2. when receiving SCCP from M3UA, check if we receive traffic that contains just SSN in the CallingParty; in that case, add the OPC from the M3UA level to the CallingParty, or
3. implement some kind of translation on trasmit, so that we can translate a CalledAddr of just a SSN into SSN+PC before handing it to M3UA

The first option is likely most in-line with what the SIGTRAN RFCs for M3UA (and SUA) would have meant, but that would remove a lot of the flexibility we currently have because we have the full CS7 code in every client application.