SS7 / SCCP design question: one or several SCCP instances?

We need to decide which way to go with point codes, sccp- and ss7-instances. pmaier and I have reached different conclusions and wrote patches going in opposite directions, now we need to decide and cosolidate: The MSC has various connections over SCCP: it serves BSSAP for several BSCs, and RANAP for several HNBGWs. BSC - A MSC: BSC -}----------> BSSAP BSC - -----> RANAP / HNBGW -}-/ IuCS HNBGW - 1) I went for exactly one point code at the MSC (say PC=1). There is exactly one osmo_ss7_instance and one osmo_sccp_instance. The MSC has separate sccp_user_bind()s for the BSSAP and the RANAP SSNs. So PC=1,SSN=BSSAP goes to the A-interface sap_up(), and PC=1,SSN=RANAP goes to the IuCS sap_up(). When comparing to the TCP/IP model, the paradigm here is that a PC is like an IP address and the SSN like a port number. At the server, the MSC, I have one PC (IP address) and listen on one SSN (port) per protocol served, and clients all connect to the same PC+SSN, receiving separate connection IDs. I can also use the calling address to know which client I'm talking to. Hence I moved the osmo_sccp_instance creation up to "the top" and created two sccp_user_bind()s, one for BSSAP and one for RANAP. This works in practice. I can tear down and set up individual sccp_users (i.e. disable/enable IuCS or A separately), and handling different clients is done by the conn_ids and possibly keeping distinct osmo_sccp_addresses. An pseudocode MSC VTY config for this scenario could look something like this: msc sccp local-pc 0.0.1 ssn-iucs $OSMO_SSN_RANAP ! -> to IuCS rx cb ssn-a $OSMO_SSN_BSSAP ! -> to A rx cb remote-bsc 1 pc 1.0.1 remote-bsc 2 pc 1.0.2 remote-hnbgw 1 pc 2.0.2 i.e. one local PC is configured, each protocol has its separate SSN, each sccp_user_bind() serves all clients for that SSN. This is the direction I took to add IuCS to AoIP. 2) pmaier added VTY configuration for various point codes, and went the other way: the MSC creates a separate osmo_sccp_instance per BSC connection. (The MSC is told the addresses of all known BSCs and) every time a BSC is configured via VTY, a new osmo_sccp_simple_client() is created. IIUC the MSC then has a distinct local PC for each BSC, and for each HNBGW. In this model there still is a code problem I noticed while adding IuCS to AoIP in OsmoMSC: if I call osmo_sccp_simple_client() a second time with a different PC, the osmo_ss7_instance used is still the same (still id=1), and notes this second PC as its global local PC. The messages received for the first client's PC are then seen as remote and routed back out -> infinite message loop. A solution here would be to either a) use a separate osmo_ss7_instance per osmo_sccp_simpe_client() (simply add an ss7 instance id parameter to osmo_sccp_simpe_client() and increment by one each time) or b) implement the routing algorithm so that it notices the local PCs of several local SCCP clients. A VTY config for this scenario so far looks like this: ! define some addresses, referenced below cs7 instance 1 sccp-address msc_local subsystem-number 254 point-code 0.0.1 routing-indicator PC sccp-address bsc_remote subsystem-number 254 point-code 0.0.2 routing-indicator PC sccp-address bsc_remote2 subsystem-number 254 point-code 0.0.3 routing-indicator PC msc bsc cs7-instance 1 calling-addr msc_local called-addr bsc_remote bsc cs7-instance 1 calling-addr msc_local called-addr bsc_remote2 (I'm not sure whether it is possible to have several sccp_instances with the same msc_local address, but we would find solutions for these petty issues once we've decided which way to go.) (I also think 'calling-addr' and 'called-addr' should rather be named 'local-addr' and 'remote-addr': depending on who calls who, the calling-addr can be the remote or the local one. That's also besides the point for now.) My personal idea is that 1) is simpler: we have one ss7 instance per program, no matter how many clients are served. I can still tear down and set up individual sccp_users (i.e. disable/enable IuCS or A separately), and handling different clients per SSN is done by the conn_ids and possibly keeping distinct osmo_sccp_addresses of the clients. 2) seems to me easier to misconfigure and it sounds to me like a paradigm of creating a whole new server for each client that connects, so instead of using an ss7_instance's routing, we create separate instances, each sending to only one counterpart. But is 2) maybe the correct way to go for reasons I'm not aware of? I notice that what I wrote is biased towards 1) because that's my POV, but this is indended to be a neutral question. We need a choice for 1) or 2) so that pmaier and I can adjust and merge our patches accordingly. Can you help us decide, hopefully with some background knowledge on how an SCCP network is intended to be set up? Thanks! ~N