cu_cp,rrc: increase default rrc guard time, remove rrc procedure extra time and improve documentation

Author: FabianEckermann

apps/units/o_cu_cp/cu_cp/cu_cp_unit_config.h

@@ -134,7 +134,9 @@ struct cu_cp_unit_mobility_config {
 struct cu_cp_unit_rrc_config {
   bool force_reestablishment_fallback = false;
   /// Guard time in ms that is added to the RRC procedure timeout.
-  unsigned rrc_procedure_guard_time_ms = 500;
+  /// NOTE: Guard time needs to be larger then SRB max retx thres * t-PollRetransmit.
+  /// (2 * default SRB maxRetxThreshold * t-PollRetransmit = 2 * 8 * 45ms = 720ms, see TS 38.331 Sec 9.2.1)
+  unsigned rrc_procedure_guard_time_ms = 1000;
 };
 
 /// Security configuration parameters.

include/srsran/cu_cp/cu_cp_configuration.h

@@ -94,7 +94,7 @@ struct cu_cp_configuration {
     /// Force re-establishment fallback.
     bool force_reestablishment_fallback = false;
     /// Guard time for RRC procedures.
-    std::chrono::milliseconds rrc_procedure_guard_time_ms{500};
+    std::chrono::milliseconds rrc_procedure_guard_time_ms{1000};
     /// Version of the RRC.
     unsigned rrc_version = 2;
   };

include/srsran/rrc/rrc_types.h

@@ -23,9 +23,6 @@
 namespace srsran {
 namespace srs_cu_cp {
 
-// Extra time that is added to RRC procedures to make sure procedures can complete.
-constexpr std::chrono::milliseconds RRC_PROCEDURE_EXTRA_TIME{500};
-
 /// Arguments for the RRC Reconfiguration procedure.
 
 struct rrc_srb_to_add_mod {

lib/rrc/ue/procedures/rrc_reconfiguration_procedure.cpp

@@ -29,7 +29,7 @@ rrc_reconfiguration_procedure::rrc_reconfiguration_procedure(rrc_ue_context_t&
   srb_notifier(srb_notifier_),
   logger(logger_)
 {
-  procedure_timeout = context.cell.timers.t311 + RRC_PROCEDURE_EXTRA_TIME + context.cfg.rrc_procedure_guard_time_ms;
+  procedure_timeout = context.cell.timers.t311 + context.cfg.rrc_procedure_guard_time_ms;
 }
 
 void rrc_reconfiguration_procedure::operator()(coro_context<async_task<bool>>& ctx)

lib/rrc/ue/procedures/rrc_reestablishment_procedure.cpp

@@ -45,7 +45,7 @@ rrc_reestablishment_procedure::rrc_reestablishment_procedure(
   event_mng(event_mng_),
   logger(logger_)
 {
-  procedure_timeout = context.cell.timers.t311 + RRC_PROCEDURE_EXTRA_TIME + context.cfg.rrc_procedure_guard_time_ms;
+  procedure_timeout = context.cell.timers.t311 + context.cfg.rrc_procedure_guard_time_ms;
 }
 
 void rrc_reestablishment_procedure::operator()(coro_context<async_task<void>>& ctx)

lib/rrc/ue/procedures/rrc_setup_procedure.cpp

@@ -37,7 +37,7 @@ rrc_setup_procedure::rrc_setup_procedure(rrc_ue_context_t&               context
   is_reestablishment_fallback(is_reestablishment_fallback_),
   logger(logger_)
 {
-  procedure_timeout = context.cell.timers.t300 + RRC_PROCEDURE_EXTRA_TIME + context.cfg.rrc_procedure_guard_time_ms;
+  procedure_timeout = context.cell.timers.t300 + context.cfg.rrc_procedure_guard_time_ms;
 }
 
 void rrc_setup_procedure::operator()(coro_context<async_task<void>>& ctx)

lib/rrc/ue/procedures/rrc_ue_capability_transfer_procedure.cpp

@@ -22,7 +22,7 @@ rrc_ue_capability_transfer_procedure::rrc_ue_capability_transfer_procedure(
     rrc_ue_logger&                              logger_) :
   context(context_), rrc_ue(rrc_ue_notifier_), event_mng(event_mng_), logger(logger_)
 {
-  procedure_timeout = RRC_PROCEDURE_EXTRA_TIME + context.cfg.rrc_procedure_guard_time_ms;
+  procedure_timeout = context.cfg.rrc_procedure_guard_time_ms;
 }
 
 void rrc_ue_capability_transfer_procedure::operator()(coro_context<async_task<bool>>& ctx)

lib/rrc/ue/rrc_ue_message_handlers.cpp

@@ -320,7 +320,7 @@ rrc_ue_security_mode_command_context rrc_ue_impl::get_security_mode_command_cont
 async_task<bool> rrc_ue_impl::handle_security_mode_complete_expected(uint8_t transaction_id)
 {
   return launch_async([this,
-                       timeout_ms = RRC_PROCEDURE_EXTRA_TIME + context.cfg.rrc_procedure_guard_time_ms,
+                       timeout_ms = context.cfg.rrc_procedure_guard_time_ms,
                        transaction_id,
                        transaction = rrc_transaction{}](coro_context<async_task<bool>>& ctx) mutable {
     CORO_BEGIN(ctx);

tests/unittests/cu_cp/cu_cp_initial_context_setup_test.cpp

@@ -318,10 +318,7 @@ TEST_F(cu_cp_initial_context_setup_test, when_ue_capability_enquiry_fails_then_i
   ASSERT_TRUE(send_security_mode_complete_and_await_ue_capability_enquiry());
 
   // Fail UE Capability Enquiry (UE doesn't respond)
-  ASSERT_FALSE(tick_until(
-      RRC_PROCEDURE_EXTRA_TIME + this->get_cu_cp_cfg().rrc.rrc_procedure_guard_time_ms,
-      [&]() { return false; },
-      false));
+  ASSERT_FALSE(tick_until(this->get_cu_cp_cfg().rrc.rrc_procedure_guard_time_ms, [&]() { return false; }, false));
 
   // Wait for NGAP Initial Context Setup Failure
   ASSERT_TRUE(await_initial_context_setup_failure());

tests/unittests/cu_cp/cu_cp_pdu_session_resource_modify_test.cpp

@@ -283,7 +283,7 @@ class cu_cp_pdu_session_resource_modify_test : public cu_cp_test_environment, pu
   {
     // Fail RRC Reconfiguration (UE doesn't respond) and wait for PDU Session Resource Setup Response
     if (tick_until(
-            rrc_test_timer_values.t310 + rrc_test_timer_values.t311 + RRC_PROCEDURE_EXTRA_TIME +
+            rrc_test_timer_values.t310 + rrc_test_timer_values.t311 +
                 this->get_cu_cp_cfg().rrc.rrc_procedure_guard_time_ms,
             [&]() { return false; },
             false)) {