NGAP Path Switch Request Acknowledge: add decode and handler

- Add handler at NGAP for Path Switch Request Acknowledge from AMF
- Add Path Switch Request Acknowledge message type definitions
- Implement decoder for Path Switch Request Acknowledge
  (Reference: 3GPP TS 38.413 §9.2.3.9)
    - AMF UE NGAP ID (M)
    - RAN UE NGAP ID (M)
    - Security Context (M)
    - PDU Session Resource Switched List (M)
    - Allowed NSSAI (M)
- Add required ASN.1 header includes for Path Switch Request Acknowledge IEs

Co-authored-by: Rakesh BB <rakesh.bb@fsid-iisc.in>
Signed-off-by: Venkatareddy Akumalla <venkatareddy.akumalla@openairinterface.org>

common/platform_constants.h

@@ -45,6 +45,8 @@
 
 #define NR_MAX_NB_PDU_SESSIONS (256)
 
+#define NR_MAX_NB_ALLOWED_SNSSAI (8) /* Maximum number of allowed S-NSSAI in TS 38.413 */
+
 #define MAX_DRBS_PER_UE         (32)  /* Maximum number of Data Radio Bearers per UE
                                        * defined for NGAP in TS 38.413 - maxnoofDRBs */
 #define MAX_PDUS_PER_UE         (8)   /* Maximum number of PDU Sessions per UE */

openair2/COMMON/ngap_messages_def.h

@@ -54,6 +54,7 @@ MESSAGE_DEF(NGAP_UL_RAN_STATUS_TRANSFER, MESSAGE_PRIORITY_MED, ngap_ran_status_t
 MESSAGE_DEF(NGAP_DL_RAN_STATUS_TRANSFER, MESSAGE_PRIORITY_MED, ngap_ran_status_transfer_t, ngap_dl_ran_status_transfer)
 MESSAGE_DEF(NGAP_RECONNECT_TIMER, MESSAGE_PRIORITY_MED, IttiMsgText, ngap_gNB_amf_data)
 MESSAGE_DEF(NGAP_PATH_SWITCH_REQ, MESSAGE_PRIORITY_MED, ngap_path_switch_req_t, ngap_path_switch_req)
+MESSAGE_DEF(NGAP_PATH_SWITCH_REQ_ACK, MESSAGE_PRIORITY_MED, ngap_path_switch_req_ack_t, ngap_path_switch_req_ack)
 
 /* NGAP -> RRC messages */
 MESSAGE_DEF(NGAP_DOWNLINK_NAS              , MESSAGE_PRIORITY_MED, ngap_downlink_nas_t              , ngap_downlink_nas )

openair2/COMMON/ngap_messages_types.h

@@ -48,6 +48,7 @@
 #define NGAP_HANDOVER_CANCEL(mSGpTR) (mSGpTR)->ittiMsg.ngap_handover_cancel
 #define NGAP_HANDOVER_CANCEL_ACK(mSGpTR) (mSGpTR)->ittiMsg.ngap_handover_cancel_ack
 #define NGAP_PATH_SWITCH_REQ(mSGpTR) (mSGpTR)->ittiMsg.ngap_path_switch_req
+#define NGAP_PATH_SWITCH_REQ_ACK(mSGpTR) (mSGpTR)->ittiMsg.ngap_path_switch_req_ack
 
 #define NGAP_UE_CONTEXT_RELEASE_REQ(mSGpTR)     (mSGpTR)->ittiMsg.ngap_ue_release_req
 #define NGAP_PDUSESSION_RELEASE_COMMAND(mSGpTR)      (mSGpTR)->ittiMsg.ngap_pdusession_release_command
@@ -686,6 +687,53 @@ typedef struct ngap_path_switch_req_s {
   pdusession_setup_t pdusessions_tobeswitched[NR_MAX_NB_PDU_SESSIONS];
 } ngap_path_switch_req_t;
 
+typedef enum ngap_security_ind_s {
+  NGAP_SECURITY_REQUIRED = 0,
+  NGAP_SECURITY_PREFERRED = 1,
+  NGAP_SECURITY_NOT_NEEDED = 2,
+} ngap_security_ind_t;
+
+/* 9.3.1.27 3GPP TS 38.413 */
+typedef struct security_ind_s {
+  ngap_security_ind_t integrity_protection_ind;
+  ngap_security_ind_t confidentiality_protection_ind;
+} security_ind_t;
+
+/* 9.3.4.9 3GPP TS 38.413 */
+typedef struct path_switch_request_ack_transfer_s {
+  // UL NG-U UP TNL Information (O)
+  gtpu_tunnel_t *n3_incoming;
+  // Security Indication (O)
+  security_ind_t *security_ind;
+} path_switch_request_ack_transfer_t;
+
+/* Path Switch Request Acknowledge 9.2.3.9 3GPP TS 38.413
+ * PDU Session Resource Switched Item */
+typedef struct path_switch_request_ack_pdusession_s {
+  // PDU Session ID (M)
+  int pdusession_id;
+  // Path Switch Request Acknowledge Transfer (M)
+  path_switch_request_ack_transfer_t pathSwitchReqAckTransfer;
+} path_switch_request_ack_pdusession_t;
+
+/* Path Switch Request Acknowledge 9.2.3.9 3GPP TS 38.413 */
+typedef struct ngap_path_switch_req_ack_s {
+  // AMF UE NGAP ID (M)
+  uint64_t amf_ue_ngap_id;
+  // RAN UE NGAP ID (M)
+  uint32_t gNB_ue_ngap_id;
+  // Security Context - Next-Hop Chaining Count (M)
+  uint8_t nh_ncc;
+  // Security Context - Next-Hop NH (M)
+  uint8_t next_security_key[SECURITY_KEY_LENGTH];
+  // List of PDU Session Resource Switched (M)
+  uint16_t nb_of_pdusessions;
+  path_switch_request_ack_pdusession_t pdusessions_switched[NR_MAX_NB_PDU_SESSIONS];
+  // Allowed NSSAI (M)
+  uint8_t nb_allowed_nssais;
+  nssai_t allowed_nssai[NR_MAX_NB_ALLOWED_SNSSAI];
+} ngap_path_switch_req_ack_t;
+
 typedef struct ngap_ue_cap_info_ind_s {
   uint32_t  gNB_ue_ngap_id;
   byte_array_t ue_radio_cap;

openair3/NGAP/ngap_gNB_handlers.c

@@ -1092,6 +1092,54 @@ static int ngap_gNB_handle_handover_cancel_ack(sctp_assoc_t assoc_id, uint32_t s
   return 0;
 }
 
+/** @brief Handler for NGAP Path Switch Request Acknowledge
+ *   AMF -> NG-RAN Node */
+static int ngap_gNB_handle_ng_path_switch_request_ack(sctp_assoc_t assoc_id, uint32_t stream, NGAP_NGAP_PDU_t *pdu)
+{
+  NGAP_INFO("Received NG Path Switch Request Acknowledge\n");
+  ngap_gNB_amf_data_t *amf_desc_p = NULL;
+  DevAssert(pdu != NULL);
+
+  if ((amf_desc_p = ngap_gNB_get_AMF(NULL, assoc_id, 0)) == NULL) {
+    NGAP_ERROR("[SCTP %u] Received Path Switch Request "
+               "Acknowledge for non existing AMF context\n", assoc_id);
+    return -1;
+  }
+  MessageDef *message_p = itti_alloc_new_message(TASK_NGAP, 0, NGAP_PATH_SWITCH_REQ_ACK);
+  ngap_path_switch_req_ack_t *msg = &NGAP_PATH_SWITCH_REQ_ACK(message_p);
+  memset(msg, 0, sizeof(*msg));
+  if (decode_ng_path_switch_request_acknowledge(msg, pdu) < 0) {
+    NGAP_ERROR("Failed to decode NG Path Switch Request Acknowledge\n");
+    free_ng_path_switch_req_ack(msg);
+    itti_free(TASK_NGAP, message_p);
+    return -1;
+  }
+
+  ngap_gNB_ue_context_t *ue_desc_p = ngap_get_ue_context(msg->gNB_ue_ngap_id);
+  if (!ue_desc_p) {
+    NGAP_ERROR("[SCTP %u] Received Path Switch Request Acknowledge for non "
+               "existing UE context (gNB_ue_ngap_id %d)\n",
+               assoc_id,
+               msg->gNB_ue_ngap_id);
+    free_ng_path_switch_req_ack(msg);
+    itti_free(TASK_NGAP, message_p);
+    return -1;
+  }
+
+  ue_desc_p->rx_stream = stream;
+  if (ue_desc_p->amf_ue_ngap_id != msg->amf_ue_ngap_id) {
+    NGAP_ERROR("UE context amf_ue_ngap_id is different from that of the message (%ld != %ld)",
+               ue_desc_p->amf_ue_ngap_id,
+               msg->amf_ue_ngap_id);
+    free_ng_path_switch_req_ack(msg);
+    itti_free(TASK_NGAP, message_p);
+    return -1;
+  }
+
+  itti_send_msg_to_task(TASK_RRC_GNB, amf_desc_p->ngap_gNB_instance->instance, message_p);
+  return 0;
+}
+
 /**
  * @brief Handle NGAP Paging message from AMF
  * @param assoc_id SCTP association ID
@@ -1542,7 +1590,7 @@ const ngap_message_decoded_callback ngap_messages_callback[][3] = {
     {0, 0, 0}, /* OverloadStart */
     {0, 0, 0}, /* OverloadStop */
     {ngap_gNB_handle_paging, 0, 0}, /* Paging */
-    {0, 0, 0}, /* PathSwitchRequest */
+    {0, ngap_gNB_handle_ng_path_switch_request_ack, 0}, /* PathSwitchRequest */
     {ngap_gNB_handle_pdusession_modify_request, 0, 0}, /* PDUSessionResourceModify */
     {0, 0, 0}, /* PDUSessionResourceModifyIndication */
     {ngap_gNB_handle_pdusession_release_command, 0, 0}, /* PDUSessionResourceRelease */

openair3/NGAP/ngap_gNB_mobility_management.c

@@ -824,3 +824,92 @@ NGAP_NGAP_PDU_t *encode_ng_path_switch_request(const ngap_path_switch_req_t *msg
   }
   return pdu;
 }
+
+void free_ng_path_switch_req_ack(ngap_path_switch_req_ack_t *msg)
+{
+  if (msg == NULL)
+    return;
+
+  for (int i = 0; i < msg->nb_of_pdusessions; i++) {
+    path_switch_request_ack_transfer_t *transfer = &msg->pdusessions_switched[i].pathSwitchReqAckTransfer;
+
+    free(transfer->n3_incoming);
+    transfer->n3_incoming = NULL;
+
+    free(transfer->security_ind);
+    transfer->security_ind = NULL;
+  }
+}
+
+/** @brief Decode NGAP Path Switch Request Acknowledge (9.2.3.9 3GPP TS 38.413) */
+int decode_ng_path_switch_request_acknowledge(ngap_path_switch_req_ack_t *msg, NGAP_NGAP_PDU_t *pdu)
+{
+  DevAssert(pdu != NULL);
+  NGAP_PathSwitchRequestAcknowledgeIEs_t *ie;
+  NGAP_PathSwitchRequestAcknowledge_t *container = &pdu->choice.successfulOutcome->value.choice.PathSwitchRequestAcknowledge;
+
+  // AMF UE NGAP ID (M)
+  NGAP_FIND_PROTOCOLIE_BY_ID(NGAP_PathSwitchRequestAcknowledgeIEs_t, ie, container, NGAP_ProtocolIE_ID_id_AMF_UE_NGAP_ID, true);
+  asn_INTEGER2ulong(&(ie->value.choice.AMF_UE_NGAP_ID), &msg->amf_ue_ngap_id);
+
+  // RAN UE NGAP ID (M)
+  NGAP_FIND_PROTOCOLIE_BY_ID(NGAP_PathSwitchRequestAcknowledgeIEs_t, ie, container, NGAP_ProtocolIE_ID_id_RAN_UE_NGAP_ID, true);
+  msg->gNB_ue_ngap_id = ie->value.choice.RAN_UE_NGAP_ID;
+
+  // Security Context (M)
+  NGAP_FIND_PROTOCOLIE_BY_ID(NGAP_PathSwitchRequestAcknowledgeIEs_t, ie, container, NGAP_ProtocolIE_ID_id_SecurityContext, true);
+  msg->nh_ncc = ie->value.choice.SecurityContext.nextHopChainingCount;
+  memcpy(msg->next_security_key, ie->value.choice.SecurityContext.nextHopNH.buf, ie->value.choice.SecurityContext.nextHopNH.size);
+
+  // PDU Session Resource Switched List (M)
+  NGAP_FIND_PROTOCOLIE_BY_ID(NGAP_PathSwitchRequestAcknowledgeIEs_t, ie, container, NGAP_ProtocolIE_ID_id_PDUSessionResourceSwitchedList, true);
+  msg->nb_of_pdusessions = ie->value.choice.PDUSessionResourceSwitchedList.list.count;
+
+  for (int i = 0; i < msg->nb_of_pdusessions; ++i) {
+    NGAP_PDUSessionResourceSwitchedItem_t *item = ie->value.choice.PDUSessionResourceSwitchedList.list.array[i];
+    path_switch_request_ack_pdusession_t *switched = &msg->pdusessions_switched[i];
+    // PDU Session ID (M)
+    switched->pdusession_id = item->pDUSessionID;
+    // Path Switch Request Acknowledge Transfer (M)
+    NGAP_PathSwitchRequestAcknowledgeTransfer_t *psrAckTransfer = NULL;
+    asn_dec_rval_t dec_rval = uper_decode_complete(NULL,
+                                                   &asn_DEF_NGAP_PathSwitchRequestAcknowledgeTransfer,
+                                                   (void **)&psrAckTransfer,
+                                                   item->pathSwitchRequestAcknowledgeTransfer.buf,
+                                                   item->pathSwitchRequestAcknowledgeTransfer.size);
+    if (dec_rval.code != RC_OK) {
+      NGAP_ERROR("Failed to decode Path Switch Request Acknowledge Transfer\n");
+      ASN_STRUCT_FREE(asn_DEF_NGAP_PathSwitchRequestAcknowledgeTransfer, psrAckTransfer);
+      return -1;
+    }
+
+    // UL NG-U UP TNL Information (O)
+    if (psrAckTransfer->uL_NGU_UP_TNLInformation != NULL) {
+      NGAP_UPTransportLayerInformation_t *up_tnl = psrAckTransfer->uL_NGU_UP_TNLInformation;
+      if (up_tnl->present == NGAP_UPTransportLayerInformation_PR_gTPTunnel && up_tnl->choice.gTPTunnel != NULL) {
+        switched->pathSwitchReqAckTransfer.n3_incoming = calloc_or_fail(1, sizeof(*switched->pathSwitchReqAckTransfer.n3_incoming));
+        OCTET_STRING_TO_INT32(&(up_tnl->choice.gTPTunnel->gTP_TEID), switched->pathSwitchReqAckTransfer.n3_incoming->teid);
+        bitstring_to_tnl(&switched->pathSwitchReqAckTransfer.n3_incoming->addr, up_tnl->choice.gTPTunnel->transportLayerAddress);
+      }
+    }
+
+    // Security Indication (O)
+    if (psrAckTransfer->securityIndication != NULL) {
+      switched->pathSwitchReqAckTransfer.security_ind = calloc_or_fail(1, sizeof(*switched->pathSwitchReqAckTransfer.security_ind));
+      switched->pathSwitchReqAckTransfer.security_ind->integrity_protection_ind = psrAckTransfer->securityIndication->integrityProtectionIndication;
+      switched->pathSwitchReqAckTransfer.security_ind->confidentiality_protection_ind = psrAckTransfer->securityIndication->confidentialityProtectionIndication;
+    }
+
+    ASN_STRUCT_FREE(asn_DEF_NGAP_PathSwitchRequestAcknowledgeTransfer, psrAckTransfer);
+  }
+
+  // Allowed NSSAI (M)
+  NGAP_FIND_PROTOCOLIE_BY_ID(NGAP_PathSwitchRequestAcknowledgeIEs_t, ie, container, NGAP_ProtocolIE_ID_id_AllowedNSSAI, true);
+  NGAP_DEBUG("AllowedNSSAI.list.count %d\n", ie->value.choice.AllowedNSSAI.list.count);
+  msg->nb_allowed_nssais = ie->value.choice.AllowedNSSAI.list.count;
+  for (int i = 0; i < msg->nb_allowed_nssais; ++i) {
+    msg->allowed_nssai[i] = decode_ngap_nssai(&ie->value.choice.AllowedNSSAI.list.array[i]->s_NSSAI);
+  }
+
+  return 0;
+}

openair3/NGAP/ngap_gNB_mobility_management.h

@@ -21,5 +21,7 @@ NGAP_NGAP_PDU_t *encode_ng_ul_ran_status_transfer(const ngap_ran_status_transfer
 NGAP_NGAP_PDU_t *encode_ng_handover_cancel(const ngap_handover_cancel_t *msg);
 int decode_ng_handover_cancel_ack(ngap_handover_cancel_ack_t *out, const NGAP_NGAP_PDU_t *pdu);
 NGAP_NGAP_PDU_t *encode_ng_path_switch_request(const ngap_path_switch_req_t *msg);
+int decode_ng_path_switch_request_acknowledge(ngap_path_switch_req_ack_t *msg, NGAP_NGAP_PDU_t *pdu);
+void free_ng_path_switch_req_ack(ngap_path_switch_req_ack_t *msg);
 
 #endif /* NGAP_GNB_MOBILITY_MANAGEMENT_H_ */

openair3/NGAP/ngap_msg_includes.h

@@ -100,4 +100,6 @@
 #include "NGAP_PDUSessionResourceToBeSwitchedDLItem.h"
 #include "NGAP_QosFlowAcceptedItem.h"
 #include "NGAP_PathSwitchRequestTransfer.h"
+#include "NGAP_PDUSessionResourceSwitchedItem.h"
+#include "NGAP_PathSwitchRequestAcknowledgeTransfer.h"
 #endif // NGAP_MSG_INCLUDES_H