E1AP: Add PDU Session Resource To Remove List to Bearer Context Modification enc/dec

According to TS 38.463 - clause 9.2.2.4 and 9.3.3.12.
Also, fix response message by encoding choice IE only
with presence of modified PDU sessions.
Co-authored-by: rmagueta <rmagueta@allbesmart.pt>

openair2/COMMON/e1ap_messages_types.h

@@ -475,6 +475,14 @@ typedef struct pdu_session_to_mod_s {
   DRB_nGRAN_to_mod_t DRBnGRanModList[E1AP_MAX_NUM_DRBS];
 } pdu_session_to_mod_t;
 
+/** PDU Session Resource To Remove List (3GPP TS 38.463 clause 9.3.3.12) */
+typedef struct {
+  // PDU Session ID (M)
+  long sessionId;
+  // Cause (O)
+  e1ap_cause_t cause;
+} pdu_session_to_remove_t;
+
 /**
  * Bearer Context Setup Request message, clause 9.2.2.1 of 3GPP TS 38.463
  */
@@ -534,6 +542,9 @@ typedef struct e1ap_bearer_mod_req_s {
   // NG-RAN PDU Session Resource To Modify List (O)
   int numPDUSessionsMod;
   pdu_session_to_mod_t pduSessionMod[E1AP_MAX_NUM_PDU_SESSIONS];
+  // NG-RAN PDU Session Resource To Remove List (O)
+  int numPDUSessionsRem;
+  pdu_session_to_remove_t pduSessionRem[E1AP_MAX_NUM_PDU_SESSIONS];
 } e1ap_bearer_mod_req_t;
 
 typedef struct e1ap_bearer_release_cmd_s {

openair2/E1AP/lib/e1ap_lib_includes.h

@@ -78,6 +78,7 @@
 #include "E1AP_DRB-To-Modify-Item-NG-RAN.h"
 #include "E1AP_PDU-Session-Resource-To-Setup-Mod-Item.h"
 #include "E1AP_DRB-To-Setup-Mod-Item-NG-RAN.h"
+#include "E1AP_PDU-Session-Resource-To-Remove-Item.h"
 // E1 Bearer Context Modification Response
 #include "E1AP_PDU-Session-Resource-Modified-Item.h"
 #include "E1AP_DRB-Modified-List-NG-RAN.h"

openair2/E1AP/tests/e1ap_lib_test.c

@@ -538,6 +538,14 @@ static void test_bearer_context_modification_request(void)
       .DRBnGRanList[0] = drb_to_setup,
   };
 
+  // PDU Session to Remove
+  pdu_session_to_remove_t pdu_session_to_remove = {
+      .sessionId = 2,
+      // Note: cause is optional extension IE, currently encoding/decoding only handles sessionId
+      .cause.type = 0,
+      .cause.value = 0,
+  };
+
   // Initialize the Bearer Context Modification Request
   e1ap_bearer_mod_req_t orig = {
       .gNB_cu_cp_ue_id = 0x1234,
@@ -548,6 +556,8 @@ static void test_bearer_context_modification_request(void)
       .pduSession[0] = pdusession_setup_item,
       .numPDUSessionsMod = 1,
       .pduSessionMod[0] = pdusession_mod_item,
+      .numPDUSessionsRem = 1,
+      .pduSessionRem[0] = pdu_session_to_remove,
   };
   *orig.bearerContextStatus = BEARER_SUSPEND;
   *orig.inactivityTimer = 1000;