Cellular Network Infrastructure » Core Network (CN) » OsmoMSC

When having incoming SGs LU REQ from the MMS while no HLR is connected, we get:

<0011> sgs_server.c:185 SGs socket bound to r=NULL<->l=0.0.0.0:29118
Mon Mar 25 17:20:23 2019 DLSS7 <001e> osmo_ss7.c:1283 0: ASP Restart for server not implemented yet!
Mon Mar 25 17:20:23 2019 DMNCC <0004> msc_main.c:604 Using internal MNCC handler.
Mon Mar 25 17:20:23 2019 DLGLOBAL <0012> telnet_interface.c:104 Available via telnet 0.0.0.0 4254
Mon Mar 25 17:20:23 2019 DSMPP <000c> smpp_smsc.c:1012 SMPP at 0.0.0.0 2775
Mon Mar 25 17:20:23 2019 DLCTRL <0019> control_if.c:911 CTRL at 0.0.0.0 4255
Mon Mar 25 17:20:23 2019 DLSMS <0018> sms_queue.c:250 Attempting to send 20 SMS
Mon Mar 25 17:20:23 2019 DLSMS <0018> sms_queue.c:234 SMS queue: no SMS to be sent
Mon Mar 25 17:20:23 2019 DLSMS <0018> sms_queue.c:261 Sending SMS done (0 attempted)
Mon Mar 25 17:20:23 2019 DLSMS <0018> sms_queue.c:317 SMSqueue added 0 messages in 0 rounds
Mon Mar 25 17:20:23 2019 DLMGCP <0022> mgcp_client.c:716 MGCP client: using endpoint domain '@mgw'
Mon Mar 25 17:20:23 2019 DLMGCP <0022> mgcp_client.c:791 MGCP GW connection: r=127.0.0.1:2427<->l=127.0.0.1:2727
Mon Mar 25 17:20:23 2019 DMSC <0006> msc_main.c:372 CS7 Instance identifiers: A = Iu = 0
Mon Mar 25 17:20:23 2019 DLSCCP <001f> sccp_user.c:397 OsmoMSC-A-Iu: Using SS7 instance 0, pc:0.23.1
Mon Mar 25 17:20:23 2019 DLSCCP <001f> sccp_user.c:415 OsmoMSC-A-Iu: Using AS instance as-clnt-OsmoMSC-A
Mon Mar 25 17:20:23 2019 DLSCCP <001f> sccp_user.c:420 OsmoMSC-A-Iu: Creating default route
Mon Mar 25 17:20:23 2019 DLSCCP <001f> sccp_user.c:476 OsmoMSC-A-Iu: Using ASP instance asp-clnt-OsmoMSC-A
Mon Mar 25 17:20:23 2019 DLSS7 <001e> osmo_ss7.c:471 0: Creating SCCP instance
Mon Mar 25 17:20:23 2019 DBSSAP <0010> a_iface.c:674 Initalizing SCCP connection to stp...
Mon Mar 25 17:20:27 2019 DSGS <0011> sgs_server.c:123 r=192.168.122.186:37270<->l=192.168.122.1:29118: Accepted new SGs connection
Mon Mar 25 17:24:41 2019 DSGS <0011> fsm.c:320 SGs-VLR-RESET(262-42-8001-01)[0x55fda7c789d0]{unknown 0}: Allocated
Mon Mar 25 17:24:41 2019 DSGS <0011> fsm.c:320 SGs-UE(num:0)[0x55fda7c760f0]{SGs-NULL}: Allocated
Mon Mar 25 17:24:41 2019 DSGS <0011> vlr_sgs_fsm.c:359 SGs-UE(num:0)[0x55fda7c760f0]{SGs-NULL}: state_chg to SGs-NULL
Mon Mar 25 17:24:41 2019 DVLR <000e> vlr.c:438 set IMSI on subscriber; IMSI=262423203001508 id=262423203001508
Mon Mar 25 17:24:41 2019 DVLR <000e> vlr.c:391 New subscr, IMSI: 262423203001508
Mon Mar 25 17:24:41 2019 DVLR <000e> vlr.c:438 set IMSI on subscriber; IMSI=262423203001508 id=262423203001508
Mon Mar 25 17:24:41 2019 DSGS <0011> vlr_sgs.c:96 SGs-UE(num:0)[0x55fda7c760f0]{SGs-NULL}: Received Event RX_LU_FROM_MME
Mon Mar 25 17:24:41 2019 DSGS <0011> vlr_sgs_fsm.c:55 SGs-UE(num:0)[0x55fda7c760f0]{SGs-NULL}: state_chg to SGs-LA-UPDATE-PRESENT
Mon Mar 25 17:24:41 2019 DVLR <000e> gsm_04_08.c:1767 SUBSCR(IMSI-262423203001508:TMSInew-0x8611AEA5) VLR: update for IMSI=262423203001508 (MSISDN=, used=1)
Mon Mar 25 17:24:41 2019 DVLR <000e> vlr.c:192 GSUP tx: 04010862423202031005f8280102
Mon Mar 25 17:24:41 2019 DLGSUP <001c> gsup_client.c:353 GSUP not connected, unable to send 04 01 08 62 42 32 02 03 10 05 f8 28 01 02 
Mon Mar 25 17:24:41 2019 DSGS <0011> vlr_sgs_fsm.c:65 SGs-UE(num:0)[0x55fda7c760f0]{SGs-LA-UPDATE-PRESENT}: (sub IMSI-262423203001508:TMSInew-0x8611AEA5) HLR LU request failed
Mon Mar 25 17:24:55 2019 DVLR <000e> vlr.c:438 set IMSI on subscriber; IMSI=262423203001508 id=262423203001508
Mon Mar 25 17:24:55 2019 DSGS <0011> vlr_sgs.c:96 SGs-UE(num:0)[0x55fda7c760f0]{SGs-LA-UPDATE-PRESENT}: Received Event RX_LU_FROM_MME
Mon Mar 25 17:24:55 2019 DSGS <0011> vlr_sgs.c:96 SGs-UE(num:0)[0x55fda7c760f0]{SGs-LA-UPDATE-PRESENT}: Event RX_LU_FROM_MME not permitted

Even after many minutes, there is no timeout or any other visible recovery. We have to consider such cases as the HLR might always be unreachable at least temporarily. What does the spec say? Shouldn't we return something at all to the MME in this case?