E1 Reestablishment

- PDCP reestablishment on CUCP (DRBs) triggering Bearer Context Modification procedures over E1
- Performing PDCP reestablishment for requested DRBs on CUUP
- Introduced function to notify re-establishment to CU-UP
- removed call to PDCP reestablishment for the DRBs on CUCP (it's done on CUUP)

cuup_notify_reestablishment:

- to fetch PDU session to setup in E1 following logic as in e1_send_bearer_updates
- fill bearer context modification request with stored F1-U tunnel information
  during E1 reestablishment, otherwise it would initialized to 0 by default
- update GTP tunnel with the stored configuration after E1 reestablishment

openair2/COMMON/e1ap_messages_types.h

@@ -125,7 +125,7 @@ typedef struct bearer_context_pdcp_config_s {
   long rLC_Mode;
   long reorderingTimer;
   long discardTimer;
-  long pDCP_Reestablishment;
+  bool pDCP_Reestablishment;
 } bearer_context_pdcp_config_t;
 
 typedef struct drb_to_setup_s {

openair2/E1AP/e1ap.c

@@ -1214,7 +1214,10 @@ static int fill_BEARER_CONTEXT_MODIFICATION_REQUEST(e1ap_bearer_setup_req_t *con
       asn1cCalloc(ieC3_1->dRB_To_Modify_List_NG_RAN, drb2Mod_List);
       asn1cSequenceAdd(drb2Mod_List->list, E1AP_DRB_To_Modify_Item_NG_RAN_t, drb2Mod);
       drb2Mod->dRB_ID = j->id;
-
+      asn1cCalloc(drb2Mod->pDCP_Configuration, pDCP_Configuration);
+      if (j->pdcp_config.pDCP_Reestablishment) {
+        asn1cCallocOne(pDCP_Configuration->pDCP_Reestablishment, E1AP_PDCP_Reestablishment_true);
+      }
       if (j->numDlUpParam > 0) {
         asn1cCalloc(drb2Mod->dL_UP_Parameters, DL_UP_Param_List);
         for (up_params_t *k = j->DlUpParamList; k < j->DlUpParamList + j->numDlUpParam; k++) {
@@ -1360,21 +1363,28 @@ static void extract_BEARER_CONTEXT_MODIFICATION_REQUEST(const E1AP_E1AP_PDU_t *p
             DRB_nGRAN_to_mod_t *drb = pdu_session->DRBnGRanModList + j;
             E1AP_DRB_To_Modify_Item_NG_RAN_t *drb2Mod = drb2ModList->list.array[j];
             drb->id = drb2Mod->dRB_ID;
-
-            E1AP_UP_Parameters_t *dl_up_paramList = drb2Mod->dL_UP_Parameters;
-            drb->numDlUpParam = dl_up_paramList->list.count;
-            for (int k = 0; k < dl_up_paramList->list.count; k++) {
-              up_params_t *dl_up_param = drb->DlUpParamList + k;
-              E1AP_UP_Parameters_Item_t *dl_up_param_in = dl_up_paramList->list.array[k];
-              if (dl_up_param_in->uP_TNL_Information.choice.gTPTunnel) { // Optional IE
-                DevAssert(dl_up_param_in->uP_TNL_Information.present = E1AP_UP_TNL_Information_PR_gTPTunnel);
-                BIT_STRING_TO_TRANSPORT_LAYER_ADDRESS_IPv4(&dl_up_param_in->uP_TNL_Information.choice.gTPTunnel->transportLayerAddress,
-                                                           dl_up_param->tlAddress);
-                OCTET_STRING_TO_INT32(&dl_up_param_in->uP_TNL_Information.choice.gTPTunnel->gTP_TEID, dl_up_param->teId);
-              } else {
-                AssertFatal(false, "gTPTunnel IE is missing. It is mandatory at this point\n");
+            if (drb2Mod->pDCP_Configuration != NULL
+                && drb2Mod->pDCP_Configuration->pDCP_Reestablishment != NULL
+                && *drb2Mod->pDCP_Configuration->pDCP_Reestablishment == E1AP_PDCP_Reestablishment_true) {
+              drb->pdcp_config.pDCP_Reestablishment = true;
+            }
+            if (drb2Mod->dL_UP_Parameters) { /* Optional IE in the DRB To Modify Item */
+              E1AP_UP_Parameters_t *dl_up_paramList = drb2Mod->dL_UP_Parameters;
+              drb->numDlUpParam = dl_up_paramList->list.count;
+              for (int k = 0; k < dl_up_paramList->list.count; k++) {
+                up_params_t *dl_up_param = drb->DlUpParamList + k;
+                E1AP_UP_Parameters_Item_t *dl_up_param_in = dl_up_paramList->list.array[k];
+                if (dl_up_param_in->uP_TNL_Information.choice.gTPTunnel) { // Optional IE
+                  DevAssert(dl_up_param_in->uP_TNL_Information.present = E1AP_UP_TNL_Information_PR_gTPTunnel);
+                  BIT_STRING_TO_TRANSPORT_LAYER_ADDRESS_IPv4(
+                      &dl_up_param_in->uP_TNL_Information.choice.gTPTunnel->transportLayerAddress,
+                      dl_up_param->tlAddress);
+                  OCTET_STRING_TO_INT32(&dl_up_param_in->uP_TNL_Information.choice.gTPTunnel->gTP_TEID, dl_up_param->teId);
+                } else {
+                  AssertFatal(false, "gTPTunnel IE is missing. It is mandatory at this point\n");
+                }
+                dl_up_param->cell_group_id = dl_up_param_in->cell_Group_ID;
               }
-              dl_up_param->cell_group_id = dl_up_param_in->cell_Group_ID;
             }
           }
         }

openair2/LAYER2/nr_pdcp/cucp_cuup_handler.c

@@ -249,6 +249,10 @@ void e1_bearer_context_modif(const e1ap_bearer_mod_req_t *req)
       DRB_nGRAN_modified_t *modified = &modif.pduSessionMod[i].DRBnGRanModList[j];
       modified->id = to_modif->id;
 
+      if (to_modif->pdcp_config.pDCP_Reestablishment) {
+        nr_pdcp_reestablishment(req->gNB_cu_up_ue_id, to_modif->id, false);
+      }
+
       if (f1inst < 0) // no F1-U?
         continue; // nothing to do
 

openair2/LAYER2/nr_pdcp/nr_pdcp_entity.c

@@ -409,6 +409,10 @@ static void free_rx_list(nr_pdcp_entity_t *entity)
   entity->rx_size = 0;
 }
 
+/**
+ * @brief PDCP entity re-establishment according to 5.1.2 of 3GPP TS 38.323
+ * @todo  deal with ciphering/integrity algos and keys for transmitting/receiving entity procedures
+*/
 static void nr_pdcp_entity_reestablish_drb_am(nr_pdcp_entity_t *entity)
 {
   /* transmitting entity procedures */

openair2/LAYER2/nr_pdcp/nr_pdcp_oai_api.c

@@ -1210,9 +1210,10 @@ void nr_pdcp_reestablishment(ue_id_t ue_id, int rb_id, bool srb_flag)
   rb = nr_pdcp_get_rb(ue, rb_id, srb_flag);
 
   if (rb != NULL) {
+    LOG_D(PDCP, "UE %4.4lx re-establishment of %sRB %d\n", ue_id, srb_flag ? "S" : "D", rb_id);
     rb->reestablish_entity(rb);
   } else {
-    LOG_W(PDCP, "UE %4.4lx cannot re-establish RB %d (is_srb %d), RB not found\n", ue_id, rb_id, srb_flag);
+    LOG_W(PDCP, "UE %4.4lx cannot re-establish %sRB %d, RB not found\n", ue_id, srb_flag ? "S" : "D", rb_id);
   }
 
   nr_pdcp_manager_unlock(nr_pdcp_ue_manager);

openair2/RRC/NR/rrc_gNB.c

@@ -902,7 +902,60 @@ static pdu_session_to_mod_t *find_or_next_pdu_session(e1ap_bearer_mod_req_t *bea
   return &bearer_modif->pduSessionMod[bearer_modif->numPDUSessionsMod - 1];
 }
 
-//-----------------------------------------------------------------------------
+/**
+ * @brief Notify E1 re-establishment to CU-UP
+ */
+static void cuup_notify_reestablishment(gNB_RRC_INST *rrc, gNB_RRC_UE_t *ue_p)
+{
+  e1ap_bearer_mod_req_t req = {
+      .gNB_cu_cp_ue_id = ue_p->rrc_ue_id,
+      .gNB_cu_up_ue_id = ue_p->rrc_ue_id,
+  };
+  if (!ue_associated_to_cuup(rrc, ue_p))
+    return;
+  /* loop through active DRBs */
+  for (int drb_id = 1; drb_id <= MAX_DRBS_PER_UE; drb_id++) {
+    if (ue_p->established_drbs[drb_id - 1].status == DRB_INACTIVE)
+      continue;
+    /* fetch an existing PDU session for this DRB */
+    rrc_pdu_session_param_t *pdu = find_pduSession_from_drbId(ue_p, drb_id);
+    if (pdu == NULL) {
+      LOG_E(RRC, "UE %d: E1 Bearer Context Modification: no PDU session for DRB ID %d\n", ue_p->rrc_ue_id, drb_id);
+      continue;
+    }
+    /* Get pointer to existing (or new one) PDU session to modify in E1 */
+    pdu_session_to_mod_t *pdu_e1 = find_or_next_pdu_session(&req, pdu->param.pdusession_id);
+    AssertError(pdu != NULL,
+                continue,
+                "UE %d: E1 Bearer Context Modification: PDU session %d to setup is null\n",
+                ue_p->rrc_ue_id,
+                pdu->param.pdusession_id);
+    /* Prepare PDU for E1 Bearear Context Modification Request */
+    pdu_e1->sessionId = pdu->param.pdusession_id;
+    /* Fill DRB to setup with ID, DL TL and DL TEID */
+    DRB_nGRAN_to_mod_t *drb_e1 = &pdu_e1->DRBnGRanModList[pdu_e1->numDRB2Modify];
+    drb_e1->id = drb_id;
+    drb_e1->numDlUpParam = 1;
+    drb_t *drbs = &ue_p->established_drbs[drb_id];
+    memcpy(&drb_e1->DlUpParamList[0].tlAddress, &drbs->f1u_tunnel_config.cuup_addr_f1u.buffer, sizeof(uint8_t) * 4);
+    drb_e1->DlUpParamList[0].teId = drbs->f1u_tunnel_config.cuup_teid_f1u;
+    /* PDCP configuration */
+    bearer_context_pdcp_config_t *pdcp_config = &drb_e1->pdcp_config;
+    drb_t *rrc_drb = get_drb(ue_p, drb_id);
+    set_bearer_context_pdcp_config(pdcp_config, rrc_drb, rrc->configuration.um_on_default_drb);
+    pdcp_config->pDCP_Reestablishment = true;
+    /* increase DRB to modify counter */
+    pdu_e1->numDRB2Modify += 1;
+  }
+  /* Send E1 Bearer Context Modification Request (3GPP TS 38.463) */
+  sctp_assoc_t assoc_id = get_existing_cuup_for_ue(rrc, ue_p);
+  rrc->cucp_cuup.bearer_context_mod(assoc_id, &req);
+}
+
+/**
+ * @brief RRCReestablishment message
+ *        Direction: Network to UE
+ */
 static void rrc_gNB_generate_RRCReestablishment(rrc_gNB_ue_context_t *ue_context_pP,
                                                 const uint8_t *masterCellGroup_from_DU,
                                                 const rnti_t old_rnti,
@@ -941,17 +994,12 @@ static void rrc_gNB_generate_RRCReestablishment(rrc_gNB_ue_context_t *ue_context
   for (int srb_id = 1; srb_id < NR_NUM_SRB; srb_id++) {
     if (ue_p->Srb[srb_id].Active) {
       nr_pdcp_config_set_security(ue_p->rrc_ue_id, srb_id, security_mode, kRRCenc, kRRCint, kUPenc);
-      // TODO: should send E1 UE Bearer Modification with PDCP Reestablishment flag
       nr_pdcp_reestablishment(ue_p->rrc_ue_id, srb_id, true);
     }
   }
-
-  // TODO: should send E1 UE Bearer Modification with PDCP Reestablishment flag
-  for (int drb_id = 1; drb_id <= MAX_DRBS_PER_UE; drb_id++) {
-    if (ue_p->established_drbs[drb_id - 1].status != DRB_INACTIVE)
-      nr_pdcp_reestablishment(ue_p->rrc_ue_id, drb_id, false);
-  }
-
+  /* PDCP Reestablishment over E1 */
+  cuup_notify_reestablishment(rrc, ue_p);
+  /* F1AP DL RRC Message Transfer */
   f1_ue_data_t ue_data = cu_get_f1_ue_data(ue_p->rrc_ue_id);
   RETURN_IF_INVALID_ASSOC_ID(ue_data);
   uint32_t old_gNB_DU_ue_id = old_rnti;
@@ -1788,7 +1836,7 @@ static void e1_send_bearer_updates(gNB_RRC_INST *rrc, gNB_RRC_UE_t *UE, int n, f
       LOG_E(RRC, "UE %d: UE Context Modif Response: no PDU session for DRB ID %ld\n", UE->rrc_ue_id, drb_f1->drb_id);
       continue;
     }
-    pdu_session_to_mod_t *pdu_e1 = find_or_next_pdu_session(&req, pdu_ue->param.pdusession_id);
+    pdu_session_to_setup_t *pdu_e1 = find_or_next_pdu_session(&req, pdu_ue->param.pdusession_id);
     DevAssert(pdu_e1 != NULL);
     pdu_e1->sessionId = pdu_ue->param.pdusession_id;
     DRB_nGRAN_to_setup_t *drb_e1 = &pdu_e1->DRBnGRanModList[pdu_e1->numDRB2Modify];