Select CU-UP based on slice

openair2/RRC/NR/nr_rrc_proto.h

@@ -133,7 +133,7 @@ rrc_gNB_generate_dedicatedRRCReconfiguration_release(
 void rrc_gNB_generate_dedicatedRRCReconfiguration(const protocol_ctxt_t *const ctxt_pP, rrc_gNB_ue_context_t *ue_context_pP);
 
 sctp_assoc_t get_existing_cuup_for_ue(const gNB_RRC_INST *rrc, const gNB_RRC_UE_t *ue);
-sctp_assoc_t get_new_cuup_for_ue(const gNB_RRC_INST *rrc, const gNB_RRC_UE_t *ue);
+sctp_assoc_t get_new_cuup_for_ue(const gNB_RRC_INST *rrc, const gNB_RRC_UE_t *ue, int sst, int sd);
 int rrc_gNB_process_e1_setup_req(sctp_assoc_t assoc_id, e1ap_setup_req_t *req);
 
 void bearer_context_setup_direct(e1ap_bearer_setup_req_t *req,

openair2/RRC/NR/rrc_gNB_NGAP.c

@@ -757,6 +757,8 @@ void rrc_gNB_process_NGAP_PDUSESSION_SETUP_REQ(MessageDef *msg_p, instance_t ins
   UE->amf_ue_ngap_id = msg->amf_ue_ngap_id;
   e1ap_bearer_setup_req_t bearer_req = {0};
 
+
+  e1ap_nssai_t cuup_nssai = {0};
   for (int i = 0; i < msg->nb_pdusessions_tosetup; i++) {
     rrc_pdu_session_param_t *pduSession = find_pduSession(UE, msg->pdusession_setup_params[i].pdusession_id, true);
     pdusession_t *session = &pduSession->param;
@@ -780,6 +782,8 @@ void rrc_gNB_process_NGAP_PDUSESSION_SETUP_REQ(MessageDef *msg_p, instance_t ins
     pdu->nssai.sd = 0xffffff;
     if (nssai->sD_flag)
       pdu->nssai.sd = nssai->sD[0] << 16 | nssai->sD[1] << 8 | nssai->sD[0];
+    if (cuup_nssai.sst == 0)
+      cuup_nssai = pdu->nssai; /* for CU-UP selection below */
     pdu->integrityProtectionIndication = rrc->security.do_drb_integrity ? E1AP_IntegrityProtectionIndication_required : E1AP_IntegrityProtectionIndication_not_needed;
 
     pdu->confidentialityProtectionIndication = rrc->security.do_drb_ciphering ? E1AP_ConfidentialityProtectionIndication_required : E1AP_ConfidentialityProtectionIndication_not_needed;
@@ -827,7 +831,12 @@ void rrc_gNB_process_NGAP_PDUSESSION_SETUP_REQ(MessageDef *msg_p, instance_t ins
   }
   int xid = rrc_gNB_get_next_transaction_identifier(instance);
   UE->xids[xid] = RRC_PDUSESSION_ESTABLISH;
-  sctp_assoc_t assoc_id = get_new_cuup_for_ue(rrc, UE);
+  /* Limitation: we assume one fixed CU-UP per UE. We base the selection on
+   * NSSAI, but the UE might have multiple PDU sessions with differing slices,
+   * in which we might need to select different CU-UPs. In this case, we would
+   * actually need to group the E1 bearer context setup for the different
+   * CU-UPs, and send them to the different CU-UPs. */
+  sctp_assoc_t assoc_id = get_new_cuup_for_ue(rrc, UE, cuup_nssai.sst, cuup_nssai.sd);
   rrc->cucp_cuup.bearer_context_setup(assoc_id, &bearer_req);
   return;
 }

openair2/RRC/NR/rrc_gNB_cuup.c

@@ -35,6 +35,29 @@ static int cuup_compare(const nr_rrc_cuup_container_t *a, const nr_rrc_cuup_cont
 /* Tree management functions */
 RB_GENERATE/*_STATIC*/(rrc_cuup_tree, nr_rrc_cuup_container_t, entries, cuup_compare);
 
+static const nr_rrc_cuup_container_t *select_cuup_slice(const struct rrc_cuup_tree *t, const gNB_RRC_UE_t *ue, int sst, int sd)
+{
+  nr_rrc_cuup_container_t *second_best_match = NULL; /* if no NSSAI matches exactly */
+  nr_rrc_cuup_container_t *cuup = NULL;
+  RB_FOREACH(cuup, rrc_cuup_tree, (struct rrc_cuup_tree *)&t) {
+    e1ap_setup_req_t *sr = cuup->setup_req;
+    for (int p = 0; p < sr->supported_plmns; ++p) {
+      /* actually we should also check that the PLMN selected by the UE matches */
+      for (int s = 0; s < sr->plmn[p].supported_slices; ++s) {
+        e1ap_nssai_t *nssai = &sr->plmn[p].slice[s];
+        if (nssai->sst == sst && nssai->sd == sd) {
+          LOG_I(RRC, "selecting CU-UP ID %ld based on exact NSSAI match (%d:0x%06x)\n", sr->gNB_cu_up_id, sst, sd);
+          return cuup; /* exact match */
+        } else if (nssai->sst == sst && second_best_match == NULL) {
+          LOG_I(RRC, "second best match: CU-UP ID %ld matches SST %d\n", sr->gNB_cu_up_id, sst);
+          second_best_match = cuup; /* only the SST matches -> "good enough" */
+        }
+      }
+    }
+  }
+  return second_best_match;
+}
+
 static const nr_rrc_cuup_container_t *select_cuup_round_robin(size_t n_t, const struct rrc_cuup_tree *t, const gNB_RRC_UE_t *ue)
 {
   /* pick the CU-UP following a "round-robin" fashion: select CU-UP M = RRC UE
@@ -42,8 +65,10 @@ static const nr_rrc_cuup_container_t *select_cuup_round_robin(size_t n_t, const
   int m = (ue->rrc_ue_id - 1) % n_t;
   nr_rrc_cuup_container_t *cuup = NULL;
   RB_FOREACH(cuup, rrc_cuup_tree, (struct rrc_cuup_tree *)&t) {
-    if (m == 0)
+    if (m == 0) {
+      LOG_I(RRC, "round-robin match: select CU-UP ID %ld (no NSSAI match)\n", cuup->setup_req->gNB_cu_up_id);
       return cuup;
+    }
     m--;
   }
   /* this should not happen: no CU-UP available? */
@@ -55,18 +80,19 @@ sctp_assoc_t get_existing_cuup_for_ue(const gNB_RRC_INST *rrc, const gNB_RRC_UE_
   f1_ue_data_t ue_data = cu_get_f1_ue_data(ue->rrc_ue_id);
   if (ue_data.e1_assoc_id == 0) {
     LOG_W(RRC, "UE %d should be associated to CU-UP, but is not\n", ue->rrc_ue_id);
-    return get_new_cuup_for_ue(rrc, ue);
+    /* we could possibly check the SST/SD from the PDU session */
+    return get_new_cuup_for_ue(rrc, ue, 0, 0);
   }
   LOG_D(RRC, "UE %d using CU-UP assoc_id %d\n", ue->rrc_ue_id, ue_data.e1_assoc_id);
   return ue_data.e1_assoc_id;
 }
 
-sctp_assoc_t get_new_cuup_for_ue(const gNB_RRC_INST *rrc, const gNB_RRC_UE_t *ue)
+sctp_assoc_t get_new_cuup_for_ue(const gNB_RRC_INST *rrc, const gNB_RRC_UE_t *ue, int sst, int sd)
 {
   /* check if there is already a UE associated */
   f1_ue_data_t ue_data = cu_get_f1_ue_data(ue->rrc_ue_id);
   if (ue_data.e1_assoc_id != 0) {
-    LOG_D(RRC, "UE %d using CU-UP assoc_id %d\n", ue->rrc_ue_id, ue_data.e1_assoc_id);
+    LOG_I(RRC, "UE %d using CU-UP assoc_id %d\n", ue->rrc_ue_id, ue_data.e1_assoc_id);
     return ue_data.e1_assoc_id;
   }
 
@@ -77,10 +103,15 @@ sctp_assoc_t get_new_cuup_for_ue(const gNB_RRC_INST *rrc, const gNB_RRC_UE_t *ue
     return 0; /* no CUUP connected */
   }
 
-  const nr_rrc_cuup_container_t *selected = select_cuup_round_robin(rrc->num_cuups, &rrc->cuups, ue);
-  if (selected == NULL)
+  const nr_rrc_cuup_container_t *selected = NULL;
+  if (sst != 0) /* only do if there is slice information */
+    selected = select_cuup_slice(&rrc->cuups, ue, sst, sd);
+  if (selected == NULL) /* nothing found yet */
+    selected = select_cuup_round_robin(rrc->num_cuups, &rrc->cuups, ue);
+  if (selected == NULL) {
     selected = RB_ROOT(&rrc->cuups);
-  AssertFatal(selected != NULL, "logic error: could not select CU-UP\n");
+  }
+  AssertFatal(selected != NULL, "logic error: could not select CU-UP, is one connected?\n");
 
   /* update the association for the UE so it will be picked up later */
   ue_data.e1_assoc_id = selected->assoc_id;