Hi, Some of my sent SMS are not received by my mobile and I try to figure out if this is a problem with my virtual layer 1, configuration or something in the layers 2+. I use: osmo-nitb: 1 subscriber in hlr (id 1, ext 017519191919) osmo-bts: virt-phy, arfcn 666, TS0=CCCH+SDCCH4, TS1=SDCCH8 MS layer23 app mobile: is the subscriber from osmo-nitb MS layer1 virt-phy: virtual gsmtap layer between bts and mobile I want: Send a sms to subscriber 017519191919. osmo-nitb VTY: OpenBSC# subscriber id 1 sms sender id 1 send Test I have 2 outcomes, first one is the failure. See https://www.dropbox.com/s/eunpfioq518t09a/mobile--ms-virt--bts-virt--bsc-ni… for the pcap. Do not wonder about the duplicated gsmtap messages from mobile, the ones to ip 225.0.0.1 are over virt-phy layer, the ones to localhost from the gsmtap logging option from mobile. Filter them out via "gsmtap && (ip.dst != 127.0.0.1)". 602-613: RR channel establishment with RA and IA as reaction to paging in 590 627,631: SABM from BTS to establish async balanced mode on SAPI3 (SMS) and the ACK from MS 656,684,699: I-Data frames on SAPI3 containing the sms 660,688,703: ReceiveReady's from MS (That ACK all I-frames before N(R)-1 as far as I understood) For me, that looks good and I really do not understand why the MS will not answer with the CP-ACK/RP-ACK after receiving the SMS Data in 699. The LAPDM link will stay up for some more time and be used by the network for retransmission of the sms (1149), but MS will never react to it on the SMS layer (CP-ACK, RP-ACK). Here is the console log for the mobile (https://www.dropbox.com/s/6gug5cd4up5qv7y/mobile--ms-virt--bts-virt--bsc-ni…). The paging is answered in line 378: Fri Mar 10 10:42:06 2017 DLLAPD <0012> lapd_core.c:793 SABM(E) received in state LAPD_STATE_IDLE Second outcome is a successfully sent sms from network to ms. See https://www.dropbox.com/s/ghdn7pc0j4vifbe/mobile--ms-virt--bts-virt--bsc-ni… for the pcap. What is different here? There is no paging, but the sms is sent within the dedicated channel used for the location update initiated by the phone started up. Why there is another outcome, I don't know. 169-181: RR channel establishment with RA and IA as part of mibiles startup routine to make location update 188,416: Location udpdate procedure on SAPI0 230,234: SABM from BTS to establish async balanced mode on SAPI3 (SMS) and the ACK from MS 396,444: I-Data frames on SAPI3 containing the sms 400,449: RR's from MS 450: CP-ACK for BTS 482,499: RP-ACK I-Frames for Network (osmo-nitb) Again, the console log of the mobile (https://www.dropbox.com/s/cujsn40d43g6wxk/mobile--ms-virt--bts-virt--bsc-ni…). The SABM on SAPI3 on downlink is received in line 206: Fri Mar 10 11:06:13 2017 DLLAPD <0012> lapd_core.c:793 SABM(E) received in state LAPD_STATE_IDLE The signaling looks quite similar in both cases, but one time the mobiles sms handler responds to CP-DATA msg containing the SMS, the other time not. Can someone find an error in the signaling I did not see? Is there a known Bug? To be honest, I last merged my branch with master some time ago (~ Jan 18 2017) and thus did not update osmo-nitb and the libraries since then to avoid compatibility problems. Have there been recent changes that could cause that behavior? Thank you and Kind Regards, Sebastian