WIP

src/mme/emm-handler.c

@@ -185,7 +185,7 @@ int emm_handle_attach_request(mme_ue_t *mme_ue,
             OGS_NAS_SECURITY_ALGORITHMS_EIA0) {
         ogs_warn("Encrypt[0x%x] can be skipped with EEA0, "
             "but Integrity[0x%x] cannot be bypassed with EIA0",
-            mme_selected_enc_algorithm(mme_ue), 
+            mme_selected_enc_algorithm(mme_ue),
             mme_selected_int_algorithm(mme_ue));
         r = nas_eps_send_attach_reject(mme_ue,
                 OGS_NAS_EMM_CAUSE_UE_SECURITY_CAPABILITIES_MISMATCH,
@@ -549,6 +549,27 @@ int emm_handle_service_request(
     return OGS_OK;
 }
 
+
+bool emm_tau_request_guti_comes_from_sgsn(const ogs_nas_eps_tracking_area_update_request_t *tau_request)
+{
+    if (tau_request->presencemask &
+        OGS_NAS_EPS_TRACKING_AREA_UPDATE_REQUEST_OLD_GUTI_TYPE_PRESENT) {
+            /* 0 = Native, 1 = Mapped */
+            return tau_request->old_guti_type.guti_type;
+    } else {
+        /* TS 23.003 2.8.2.2.2:
+            * "The most significant bit of the <LAC> shall be set to zero;
+            * and the most significant bit of <MME group id> shall be set to
+            * one. Based on this definition, the most significant bit of the
+            * <MME group id> can be used to distinguish the node type, i.e.
+            * whether it is an MME or SGSN */
+        const ogs_nas_eps_mobile_identity_t *eps_mobile_identity = &tau_request->old_guti;
+        if (eps_mobile_identity->imsi.type != OGS_NAS_EPS_MOBILE_IDENTITY_GUTI)
+            return false;
+        return !(eps_mobile_identity->guti.mme_gid & 0x8000);
+    }
+}
+
 int emm_handle_tau_request(mme_ue_t *mme_ue,
     ogs_nas_eps_tracking_area_update_request_t *tau_request, ogs_pkbuf_t *pkbuf)
 {
@@ -679,6 +700,10 @@ int emm_handle_tau_request(mme_ue_t *mme_ue,
                 nas_guti.m_tmsi,
                 MME_UE_HAVE_IMSI(mme_ue)
                     ? mme_ue->imsi_bcd : "Unknown");
+
+        memcpy(&mme_ue->next.guti,
+           &nas_guti, sizeof(ogs_nas_eps_guti_t));
+
         break;
     default:
         ogs_error("Not implemented[%d]", eps_mobile_identity->imsi.type);

src/mme/emm-handler.h

@@ -50,6 +50,9 @@ int emm_handle_extended_service_request(mme_ue_t *mme_ue,
 int emm_handle_security_mode_complete(mme_ue_t *mme_ue,
     ogs_nas_eps_security_mode_complete_t *security_mode_complete);
 
+bool emm_tau_request_guti_comes_from_sgsn(
+    const ogs_nas_eps_tracking_area_update_request_t *tau_request);
+
 #ifdef __cplusplus
 }
 #endif

src/mme/emm-sm.c

@@ -20,6 +20,7 @@
 #include "mme-event.h"
 #include "mme-timer.h"
 #include "s1ap-handler.h"
+#include "mme-gn-handler.h"
 #include "mme-fd-path.h"
 #include "emm-handler.h"
 #include "emm-build.h"
@@ -285,7 +286,9 @@ static void common_register_state(ogs_fsm_t *s, mme_event_t *e,
 
     mme_ue_t *mme_ue = NULL;
     enb_ue_t *enb_ue = NULL;
+    mme_sgsn_t *sgsn = NULL;
     ogs_nas_eps_message_t *message = NULL;
+    ogs_nas_rai_t rai;
     ogs_nas_security_header_type_t h;
 
     ogs_assert(e);
@@ -488,6 +491,25 @@ static void common_register_state(ogs_fsm_t *s, mme_event_t *e,
                 break;
             }
 
+            if (emm_tau_request_guti_comes_from_sgsn(&message->emm.tracking_area_update_request)) {
+                ogs_info("TAU request : UE comes from SGSN, attempt retrieving context");
+                guti_to_rai_ptmsi(&mme_ue->next.guti, &rai, NULL, NULL);
+                sgsn = mme_sgsn_find_by_routing_address(&rai, 0xffff);
+                if (!sgsn) {
+                    ogs_plmn_id_t plmn_id;
+                    ogs_nas_from_plmn_id(&rai.lai.nas_plmn_id, &plmn_id);
+                    ogs_warn("No SGSN route matching RAI[MCC:%u MNC:%u LAC:%u RAC:%u]",
+                             ogs_plmn_id_mcc(&plmn_id), ogs_plmn_id_mnc(&plmn_id),
+                             rai.lai.lac, rai.rac);
+                    r = nas_eps_send_tau_reject(mme_ue,
+                    OGS_NAS_EMM_CAUSE_UE_IDENTITY_CANNOT_BE_DERIVED_BY_THE_NETWORK);
+                    OGS_FSM_TRAN(s, &emm_state_exception);
+                }
+                mme_gtp1_send_sgsn_context_request(sgsn, mme_ue);
+                OGS_FSM_TRAN(s, &emm_state_registered); /* FIXME: use a specific FSM state here? */
+                break;
+            }
+
             if (!MME_UE_HAVE_IMSI(mme_ue)) {
                 ogs_info("TAU request : Unknown UE");
                 r = nas_eps_send_tau_reject(mme_ue,

src/mme/mme-context.c

@@ -2488,6 +2488,15 @@ mme_sgsn_t *mme_sgsn_find_by_routing_address(const ogs_nas_rai_t *rai, uint16_t
         }
     }
 
+    /* If no exact match found, try using any with same RAI: */
+    ogs_list_for_each(&self.sgsn_list, sgsn) {
+        mme_sgsn_route_t *rt = NULL;
+        ogs_list_for_each(&sgsn->route_list, rt) {
+            if (memcmp(&rt->rai, rai, sizeof(ogs_nas_rai_t)) == 0)
+                return sgsn;
+        }
+    }
+
     /* No route found, return default route if available: */
     return mme_sgsn_find_by_default_routing_address();
 }

src/mme/mme-gn-build.c

@@ -177,6 +177,26 @@ static int sess_fill_pdp_context_decoded(mme_sess_t *sess, ogs_gtp1_pdp_context_
     return OGS_OK;
 }
 
+/* 3GPP TS 29.060 7.5.3 SGSN Context Request */
+ogs_pkbuf_t *mme_gn_build_sgsn_context_request(
+                mme_ue_t *mme_ue)
+{
+    ogs_gtp1_message_t gtp1_message;
+    ogs_gtp1_sgsn_context_request_t *req = NULL;
+
+    ogs_debug("[Gn] build SGSN Context Request");
+
+    ogs_assert(mme_ue);
+
+    req = &gtp1_message.sgsn_context_request;
+    memset(&gtp1_message, 0, sizeof(ogs_gtp1_message_t));
+
+    (void)req;
+
+    gtp1_message.h.type = OGS_GTP1_SGSN_CONTEXT_REQUEST_TYPE;
+    return ogs_gtp1_build_msg(&gtp1_message);
+}
+
 /* 3GPP TS 29.060 7.5.4 SGSN Context Response */
 ogs_pkbuf_t *mme_gn_build_sgsn_context_response(
                 mme_ue_t *mme_ue, uint8_t cause)

src/mme/mme-gn-build.h

@@ -33,6 +33,9 @@ extern "C" {
 ogs_pkbuf_t *mme_gn_build_sgsn_context_response(
                 mme_ue_t *mme_ue, uint8_t cause);
 
+ogs_pkbuf_t *mme_gn_build_sgsn_context_request(
+                mme_ue_t *mme_ue);
+
 ogs_pkbuf_t *mme_gn_build_ran_information_relay(
                 uint8_t type, const uint8_t *buf, size_t len,
                 const ogs_nas_rai_t *rai, uint16_t cell_id);

src/mme/mme-gn-handler.c

@@ -68,10 +68,25 @@ static int decode_global_enb_id(S1AP_Global_ENB_ID_t *glob_enb_id, const uint8_t
     return OGS_OK;
 }
 
-/* 3GPP TS 23.003 2.8.2.2 Mapping from RAI and P-TMSI to GUT */
+/* 3GPP TS 23.003 2.8.2.1 Mapping from GUTI to RAI, P-TMSI and P-TMSI signature */
+void guti_to_rai_ptmsi(const ogs_nas_eps_guti_t *nas_guti, ogs_nas_rai_t *rai, mme_p_tmsi_t *ptmsi, uint32_t *ptmsi_sig)
+{
+    rai->lai.nas_plmn_id = nas_guti->nas_plmn_id;
+    rai->lai.lac = htobe16(nas_guti->mme_gid);
+    rai->rac = nas_guti->mme_code;
+    if (ptmsi)
+        *ptmsi = 0xC0000000 |
+                (nas_guti->m_tmsi & 0x3f000000) |
+                (nas_guti->mme_code & 0x0ff) << 16 |
+                (nas_guti->m_tmsi & 0x0000ffff);
+    if (ptmsi_sig)
+        *ptmsi_sig = (nas_guti->m_tmsi & 0x00ff0000);
+}
+
+/* 3GPP TS 23.003 2.8.2.2 Mapping from RAI and P-TMSI to GUTI */
 static void rai_ptmsi_to_guti(const ogs_nas_rai_t *rai, mme_p_tmsi_t ptmsi, uint32_t ptmsi_sig, ogs_nas_eps_guti_t *nas_guti)
 {
-    uint16_t lac = be16toh(rai->lai.lac);;
+    uint16_t lac = be16toh(rai->lai.lac);
     nas_guti->nas_plmn_id =rai->lai.nas_plmn_id;
     nas_guti->mme_gid = lac;
     nas_guti->mme_code = rai->rac;

src/mme/mme-gn-handler.h

@@ -41,6 +41,9 @@ void mme_gn_handle_sgsn_context_acknowledge(
 void mme_gn_handle_ran_information_relay(
         ogs_gtp_xact_t *xact, ogs_gtp1_ran_information_relay_t *req);
 
+void guti_to_rai_ptmsi(const ogs_nas_eps_guti_t *nas_guti, ogs_nas_rai_t *rai,
+        mme_p_tmsi_t *ptmsi, uint32_t *ptmsi_sig);
+
 #ifdef __cplusplus
 }
 #endif

src/mme/mme-gtp-path.c

@@ -758,6 +758,45 @@ int mme_gtp_send_bearer_resource_command(
     return rv;
 }
 
+/*************************
+ * GTPv1C (Gn interface):
+ *************************/
+
+int mme_gtp1_send_sgsn_context_request(
+        mme_sgsn_t *sgsn, mme_ue_t *mme_ue)
+{
+    int rv;
+    ogs_gtp1_header_t h;
+    ogs_pkbuf_t *pkbuf = NULL;
+    ogs_gtp_xact_t *xact = NULL;
+
+    ogs_assert(sgsn);
+
+    memset(&h, 0, sizeof(ogs_gtp1_header_t));
+    h.type = OGS_GTP1_SGSN_CONTEXT_REQUEST_TYPE;
+    h.teid = 0;
+
+    pkbuf = mme_gn_build_sgsn_context_request(mme_ue);
+    if (!pkbuf) {
+        ogs_error("mme_gn_build_ran_information_relay() failed");
+        return OGS_ERROR;
+    }
+
+    xact = ogs_gtp1_xact_local_create(&sgsn->gnode, &h, pkbuf, NULL, NULL);
+    if (!xact) {
+        ogs_error("ogs_gtp1_xact_local_create() failed");
+        return OGS_ERROR;
+    }
+    /* TS 29.060 8.2: "The SGSN Context Request message, where the Tunnel
+     * Endpoint Identifier shall be set to all zeroes." */
+    xact->local_teid = 0;
+
+    rv = ogs_gtp_xact_commit(xact);
+    ogs_expect(rv == OGS_OK);
+
+    return rv;
+}
+
 int mme_gtp1_send_sgsn_context_response(
         mme_ue_t *mme_ue, uint8_t cause, ogs_gtp_xact_t *xact)
 {

src/mme/mme-gtp-path.h

@@ -55,6 +55,9 @@ int mme_gtp_send_delete_indirect_data_forwarding_tunnel_request(
 int mme_gtp_send_bearer_resource_command(
         mme_bearer_t *bearer, ogs_nas_eps_message_t *nas_message);
 
+int mme_gtp1_send_sgsn_context_request(
+        mme_sgsn_t *sgsn, mme_ue_t *mme_ue);
+
 int mme_gtp1_send_sgsn_context_response(
         mme_ue_t *mme_ue, uint8_t cause, ogs_gtp_xact_t *xact);