stefano_77 grazie!
disabilitando il solo SIP ALG non risolvo. circa il port forwarding, intendi che devo forwardare la UDP 5060 (SIP) esterna sulla UDP 5060 (SIP) interna, e stessa cosa con l'altro gruppo di porte?
guardando i log e cercando "error" trovo questo blocco di log, non so se pertinenti
Jun 13 10:23:44 ATP [1262.1271]: ATP <6+info > [LIB_ATP]atp service get status
Jun 13 10:23:44 ATP [1262.1271]: ATP <3+error > [LIB_ATP]atp api call failed, caller(68248), msg(30264), wp(0), lp(16).
Jun 13 10:23:44 ATP [1262.1271]: ATP <6+info > [LIB_ATP]atp service get status
Jun 13 10:23:44 ATP [1262.1271]: ATP <3+error > [LIB_ATP]atp api call failed, caller(68248), msg(30264), wp(0), lp(17).
Jun 13 10:23:44 ATP [1262.1271]: ATP <6+info > [LIB_ATP]atp service get status
Jun 13 10:23:44 ATP [1262.1271]: ATP <3+error > [LIB_ATP]atp api call failed, caller(68248), msg(30264), wp(0), lp(18).
Jun 13 10:23:44 sua [1148.1148]: APP <6+info > [SIP] <IPC_rcv >:msg:0x00000081, wparam:0, lparam:0, id:Undefied on small space device, data_ptr=(nil)
Jun 13 10:23:44 ipvp[1110.1110]: IPVP<5+notice> 024.388.427:Message=0x00000081(0x00000000+0x00000000+0)
Jun 13 10:23:44 ipvp[1110.1110]: IPVP<6+info > 024.388.758:get MKIT_MSG_STATS, dump type 0,dump_level:0
Jun 13 10:23:44 ipvp[1110.1110]: IPVP<6+info > 024.390.376:dump len:5784
Jun 13 10:23:44 WEB [1445:1451]: WEB <6+info > 024.693.640:CWebMsgThread::OnOutputDump, dump type 0
Jun 13 10:23:44 sys [872.877]: SYS <5+notice> req for process status
Jun 13 10:23:44 sys [872.877]: SYS <5+notice> req for process status end
Jun 13 10:23:44 sys [872.877]: SYS <6+info > dump to file end