[mle] delay to send announce for FTD (#2521)

src/core/thread/mle.cpp

@@ -644,13 +644,8 @@ otError Mle::SetStateChild(uint16_t aRloc16)
     netif.GetIp6().SetForwardingEnabled(false);
     netif.GetIp6().GetMpl().SetTimerExpirations(kMplChildDataMessageTimerExpirations);
 
-    // Once the Thread device receives the new Active Commissioning Dataset, the device MUST
-    // transmit its own Announce messages on the channel it was on prior to the attachment.
-    if (mPreviousPanId != Mac::kPanIdBroadcast)
-    {
-        mPreviousPanId = Mac::kPanIdBroadcast;
-        netif.GetAnnounceBeginServer().SendAnnounce(1 << mPreviousChannel);
-    }
+    // send announce after attached if needed
+    InformPreviousChannel();
 
 #if OPENTHREAD_CONFIG_ENABLE_PERIODIC_PARENT_SEARCH
     UpdateParentSearchState();
@@ -665,6 +660,23 @@ otError Mle::SetStateChild(uint16_t aRloc16)
     return OT_ERROR_NONE;
 }
 
+void Mle::InformPreviousChannel(void)
+{
+    VerifyOrExit(mPreviousPanId != Mac::kPanIdBroadcast);
+    VerifyOrExit(mRole == OT_DEVICE_ROLE_CHILD || mRole == OT_DEVICE_ROLE_ROUTER);
+
+    if ((mDeviceMode & ModeTlv::kModeFFD) == 0 ||
+        mRole == OT_DEVICE_ROLE_ROUTER ||
+        GetNetif().GetMle().GetRouterSelectionJitterTimeout() == 0)
+    {
+        mPreviousPanId = Mac::kPanIdBroadcast;
+        GetNetif().GetAnnounceBeginServer().SendAnnounce(1 << mPreviousChannel);
+    }
+
+exit:
+    return;
+}
+
 otError Mle::SetTimeout(uint32_t aTimeout)
 {
     VerifyOrExit(mTimeout != aTimeout);

src/core/thread/mle.hpp

@@ -1360,6 +1360,16 @@ protected:
      */
     void LogMleMessage(const char *aLogMessage, const Ip6::Address &aAddress, uint16_t aRloc) const;
 
+    /**
+     * This method triggers MLE Announce on previous channel after the Thread device successfully
+     * attaches and receives the new Active Commissioning Dataset if needed.
+     *
+     * MTD would send Announce immediately after attached.
+     * FTD would delay to send Announce after tried to become Router or decided to stay in REED role.
+     *
+     */
+    void InformPreviousChannel(void);
+
     LeaderDataTlv mLeaderData;              ///< Last received Leader Data TLV.
     bool mRetrieveNewNetworkData;           ///< Indicating new Network Data is needed if set.
 

src/core/thread/mle_router.cpp

@@ -1871,6 +1871,11 @@ void MleRouter::HandleStateUpdateTimer(void)
                 // upgrade to Router
                 BecomeRouter(ThreadStatusTlv::kTooFewRouters);
             }
+            else
+            {
+                // send announce after decided to stay in REED if needed
+                InformPreviousChannel();
+            }
 
             if (!mAdvertiseTimer.IsRunning())
             {
@@ -4360,6 +4365,10 @@ void MleRouter::HandleAddressSolicitResponse(Coap::Header *aHeader, Message *aMe
     }
 
 exit:
+
+    // send announce after received address solicit reply if needed
+    InformPreviousChannel();
+
     return;
 }
 

src/core/thread/mle_router_ftd.hpp

@@ -301,6 +301,14 @@ public:
      */
     otError SetRouterSelectionJitter(uint8_t aRouterJitter);
 
+    /**
+     * This method returns the current router selection jitter timeout value.
+     *
+     * @returns The current router selection jitter timeout value.
+     *
+     */
+    uint8_t GetRouterSelectionJitterTimeout(void) { return mRouterSelectionJitterTimeout; }
+
     /**
      * This method returns the current Router ID Sequence value.
      *

src/core/thread/mle_router_mtd.hpp

@@ -59,6 +59,7 @@ public:
 
     uint8_t GetActiveRouterCount(void) const { return 0; }
     uint8_t GetActiveNeighborRouterCount(void) const { return 0; }
+    uint8_t GetRouterSelectionJitterTimeout(void) { return 0; }
 
     uint32_t GetLeaderAge(void) const { return 0; }