update mrp calculation

-- Use 15 seconds to determine whether device is in LIT mode, then if
yes, set the timeout base as SAI if GetRemoteMRPConfig().mIdleRetransTimeout.count() > sitIcdSlowPollMaximum.count()

Author: yunhanw-google

src/messaging/ReliableMessageProtocolConfig.cpp

@@ -133,10 +133,15 @@ System::Clock::Timeout GetRetransmissionTimeout(System::Clock::Timeout activeInt
     // Calculate the retransmission timeout and take into account that an active/idle state change can happen
     // in the middle.
     System::Clock::Timestamp timeout(0);
+    System::Clock::Milliseconds32 sitIcdSlowPollMaximum = System::Clock::Milliseconds32(15000);
     for (uint8_t i = 0; i < CHIP_CONFIG_RMP_DEFAULT_MAX_RETRANS + 1; i++)
     {
-        auto baseInterval =
-            ((timeSinceLastActivity + timeout) < activityThreshold) ? activeInterval : min(activeInterval, idleInterval);
+        auto baseInterval = activeInterval;
+        if ((timeSinceLastActivity + timeout) >= activityThreshold) && 
+        (idleInterval.count() <= sitIcdSlowPollMaximum.count()))
+        {
+            baseInterval = idleInterval;
+        }
         timeout += Messaging::ReliableMessageMgr::GetBackoff(baseInterval, i, /* computeMaxPossible */ true);
     }
 

src/transport/SecureSession.h

@@ -265,8 +265,16 @@ class SecureSession : public Session, public ReferenceCounted<SecureSession, Sec
 
     System::Clock::Timestamp GetMRPBaseTimeout() const override
     {
-        return IsPeerActive() ? GetRemoteMRPConfig().mActiveRetransTimeout
-                              : min(GetRemoteMRPConfig().mActiveRetransTimeout, GetRemoteMRPConfig().mIdleRetransTimeout);
+        System::Clock::Milliseconds32 sitIcdSlowPollMaximum = System::Clock::Milliseconds32(15000);
+        if (IsPeerActive())
+        {
+            return GetRemoteMRPConfig().mActiveRetransTimeout;
+        }
+        if (GetRemoteMRPConfig().mIdleRetransTimeout.count() <= sitIcdSlowPollMaximum.count())
+        {
+            return GetRemoteMRPConfig().mIdleRetransTimeout;
+        }
+        return GetRemoteMRPConfig().mActiveRetransTimeout;
     }
 
     CryptoContext & GetCryptoContext() { return mCryptoContext; }

src/transport/UnauthenticatedSessionTable.h

@@ -155,8 +155,16 @@ class UnauthenticatedSession : public Session, public ReferenceCounted<Unauthent
 
     System::Clock::Timestamp GetMRPBaseTimeout() const override
     {
-        return IsPeerActive() ? GetRemoteMRPConfig().mActiveRetransTimeout
-                              : min(GetRemoteMRPConfig().mActiveRetransTimeout, GetRemoteMRPConfig().mIdleRetransTimeout);
+        System::Clock::Milliseconds32 sitIcdSlowPollMaximum = System::Clock::Milliseconds32(15000);
+        if (IsPeerActive())
+        {
+            return GetRemoteMRPConfig().mActiveRetransTimeout;
+        }
+        if (GetRemoteMRPConfig().mIdleRetransTimeout.count() <= sitIcdSlowPollMaximum.count())
+        {
+            return GetRemoteMRPConfig().mIdleRetransTimeout;
+        }
+        return GetRemoteMRPConfig().mActiveRetransTimeout;
     }
 
     void SetRemoteSessionParameters(const SessionParameters & sessionParams) { mRemoteSessionParams = sessionParams; }