[lte][agw] Store admitted E-RABs during handover (#6257)

Indicate no data forwarding supported during S1 handover, and store
resulting E-RABs from the target eNBs in the UE state for updating
bearers when procedure is complete.

Signed-off-by: Shaddi Hasan <shasan@fb.com>

lte/gateway/c/oai/include/s1ap_types.h

@@ -20,6 +20,7 @@
 #include <stdint.h>
 
 #include "3gpp_36.401.h"
+#include "3gpp_36.413.h"
 
 #include "common_types.h"
 #include "hashtable.h"
@@ -87,6 +88,7 @@ typedef struct s1ap_handover_state_s {
       target_enb_ue_s1ap_id : 24;  ///< Unique UE id over eNB (24 bits wide)
   sctp_stream_id_t target_sctp_stream_recv;  ///< eNB -> MME stream
   sctp_stream_id_t target_sctp_stream_send;  ///< MME -> eNB stream
+  e_rab_admitted_list_t e_rab_admitted_list;
 } s1ap_handover_state_t;
 
 /** Main structure representing UE association over s1ap
@@ -116,7 +118,9 @@ typedef struct ue_description_s {
   // UE Context Release procedure guard timer
   struct s1ap_timer_t s1ap_ue_context_rel_timer;
 
-  // Handover status
+  // Handover status. We intentionally do not persist all of this state since
+  // it's time sensitive; if the MME restarts during a HO procedure the RAN
+  // will abort the procedure due to timeouts, rendering this state useless.
   s1ap_handover_state_t s1ap_handover_state;
 } ue_description_t;
 

lte/gateway/c/oai/lib/3gpp/3gpp_36.413.h

@@ -154,6 +154,19 @@ typedef struct e_rab_to_be_setup_list_ho_req_s {
   e_rab_to_be_setup_item_ho_req_t item[MAX_NO_OF_E_RABS];
 } e_rab_to_be_setup_list_ho_req_t;
 
+// 9.1.5.5 HANDOVER REQUEST ACK
+typedef struct e_rab_admitted_item_s {
+  e_rab_id_t e_rab_id;
+  bstring transport_layer_address;
+  teid_t gtp_teid;
+  // TODO: Include optional UL and DL tunnels for indirect forwarding
+} e_rab_admitted_item_t;
+
+typedef struct e_rab_admitted_list_s {
+  uint16_t no_of_items;
+  e_rab_admitted_item_t item[MAX_NO_OF_E_RABS];
+} e_rab_admitted_list_t;
+
 // E-RAB TO BE MODIFIED ITEM BEARER MOD IND
 typedef struct e_rab_to_be_modified_bearer_mod_ind_s {
   e_rab_id_t e_rab_id;

lte/gateway/c/oai/tasks/mme_app/mme_app_bearer.c

@@ -3381,8 +3381,6 @@ void mme_app_handle_handover_request_ack(
       bstrcpy(handover_request_ack_p
                   ->tgt_src_container);  // ownership passed to receiver
 
-  // TODO: set up E-RABs. As is, HO will proceed, but we will drop packets.
-
   OAILOG_INFO_UE(
       LOG_MME_APP, ue_context_p->emm_context._imsi64,
       "MME_APP send HANDOVER_COMMAND to S1AP for ue_id %d \n",

lte/gateway/c/oai/tasks/s1ap/s1ap_mme_handlers.c

@@ -1925,6 +1925,7 @@ int s1ap_mme_handle_handover_request_ack(
   enb_ue_s1ap_id_t tgt_enb_ue_s1ap_id          = INVALID_ENB_UE_S1AP_ID;
   S1ap_HandoverType_t handover_type            = -1;
   bstring tgt_src_container                    = {0};
+  e_rab_admitted_list_t e_rab_list             = {0};
   imsi64_t imsi64                              = INVALID_IMSI64;
   s1ap_imsi_map_t* imsi_map                    = get_s1ap_imsi_map();
 
@@ -1957,9 +1958,34 @@ int s1ap_mme_handle_handover_request_ack(
   }
 
   // E-RABAdmittedList: mandatory
-  // Note that the DL and UL transport address and GTP-TEID are optional, and
-  // only used if data forwarding will take place.
-  // TODO: add support for indirect data forwarding
+  S1AP_FIND_PROTOCOLIE_BY_ID(
+      S1ap_HandoverRequestAcknowledgeIEs_t, ie, container,
+      S1ap_ProtocolIE_ID_id_E_RABAdmittedList, true);
+  if (ie) {
+    S1ap_E_RABAdmittedList_t* erab_admitted_list_req =
+        &ie->value.choice.E_RABAdmittedList;
+    int num_erab = ie->value.choice.E_RABAdmittedList.list.count;
+    for (int i = 0; i < num_erab; i++) {
+      S1ap_E_RABAdmittedItemIEs_t* erab_admitted_item_ies =
+          (S1ap_E_RABAdmittedItemIEs_t*) erab_admitted_list_req->list.array[i];
+      S1ap_E_RABAdmittedItem_t* erab_admitted_item_req =
+          (S1ap_E_RABAdmittedItem_t*) &erab_admitted_item_ies->value.choice
+              .E_RABAdmittedItem;
+      e_rab_list.item[i].e_rab_id = erab_admitted_item_req->e_RAB_ID;
+      e_rab_list.item[i].transport_layer_address = blk2bstr(
+          erab_admitted_item_req->transportLayerAddress.buf,
+          erab_admitted_item_req->transportLayerAddress.size);
+      e_rab_list.item[i].gtp_teid =
+          htonl(*((uint32_t*) erab_admitted_item_req->gTP_TEID.buf));
+      // TODO: Add support for indirect data forwarding. Note that the DL and UL
+      // transport address and GTP-TEID are optional, and only used if data
+      // forwarding will take place. Since we don't currently support data
+      // forwarding, these are ignored.
+      e_rab_list.no_of_items += 1;
+    }
+  } else {
+    OAILOG_FUNC_RETURN(LOG_S1AP, RETURNerror);
+  }
 
   // Target To Source Transparent Container: mandatory
   S1AP_FIND_PROTOCOLIE_BY_ID(
@@ -2018,8 +2044,12 @@ int s1ap_mme_handle_handover_request_ack(
   // it's an intralte handover.
   handover_type = S1ap_HandoverType_intralte;
 
-  // Since we aren't doing data forwarding yet, we could directly create the
-  // HandoverCommand. We'll pass the message through the MME_APP still.
+  // Add the e_rab_list to the UE's handover state -- we'll modify the bearers
+  // if and when we receive the HANDOVER NOTIFY later in the procedure, so we
+  // need to keep track of this.
+  if (e_rab_list.no_of_items) {
+    ue_ref_p->s1ap_handover_state.e_rab_admitted_list = e_rab_list;
+  }
 
   s1ap_mme_itti_s1ap_handover_request_ack(
       mme_ue_s1ap_id, ue_ref_p->enb_ue_s1ap_id, tgt_enb_ue_s1ap_id,
@@ -2187,6 +2217,32 @@ int s1ap_mme_handle_handover_request(
         ho_request_p->e_rab_list.item[i]
             .e_rab_level_qos_parameters.allocation_and_retention_priority
             .pre_emption_vulnerability;
+
+    // data forwarding not supported
+    OAILOG_INFO(LOG_S1AP, "Note: data forwarding unsupported\n");
+    S1ap_E_RABToBeSetupItemHOReq_ExtIEs_t* exts =
+        (S1ap_E_RABToBeSetupItemHOReq_ExtIEs_t*) calloc(
+            1, sizeof(S1ap_E_RABToBeSetupItemHOReq_ExtIEs_t));
+    exts->id          = S1ap_ProtocolIE_ID_id_Data_Forwarding_Not_Possible;
+    exts->criticality = S1ap_Criticality_ignore;
+    exts->extensionValue.present =
+        S1ap_E_RABToBeSetupItemHOReq_ExtIEs__extensionValue_PR_Data_Forwarding_Not_Possible;
+    exts->extensionValue.choice.Data_Forwarding_Not_Possible =
+        S1ap_Data_Forwarding_Not_Possible_data_Forwarding_not_Possible;
+
+    S1ap_ProtocolExtensionContainer_7327P1_t* xc =
+        (S1ap_ProtocolExtensionContainer_7327P1_t*) calloc(
+            1, sizeof(S1ap_ProtocolExtensionContainer_7327P1_t));
+    int asn_ret = 0;
+    asn_ret     = ASN_SEQUENCE_ADD(&xc->list, exts);
+    if (asn_ret) {
+      OAILOG_ERROR(LOG_S1AP, "ASN_SEQUENCE_ADD ret = %d\n", asn_ret);
+    }
+
+    // Bad cast...
+    e_RABToBeSetup->iE_Extensions =
+        (struct S1ap_ProtocolExtensionContainer*) xc;
+
     ASN_SEQUENCE_ADD(&e_rab_to_be_setup_list->list, e_rab_tobesetup_item);
   }