From 827555139c8390911f12860330febd08e2bf4610 Mon Sep 17 00:00:00 2001
From: Buke Po <bukepo@gmail.com>
Date: Fri, 17 Feb 2017 06:00:07 +0800
Subject: [PATCH] reattach when parent fails to respond to child update request
 (#1330)

---
 src/core/thread/mle.cpp | 15 +++++++++++++--
 src/core/thread/mle.hpp |  1 +
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/src/core/thread/mle.cpp b/src/core/thread/mle.cpp
index 2cf37b000..30ed28780 100644
--- a/src/core/thread/mle.cpp
+++ b/src/core/thread/mle.cpp
@@ -539,6 +539,7 @@ ThreadError Mle::SetStateChild(uint16_t aRloc16)
 
     if ((mDeviceMode & ModeTlv::kModeRxOnWhenIdle) != 0)
     {
+        mKeepAliveAttemptsSent = 0;
         mParentRequestTimer.Start(Timer::SecToMsec(mTimeout / kMaxChildKeepAliveAttempts));
     }
 
@@ -1256,8 +1257,17 @@ void Mle::HandleParentRequestTimer(void)
         {
             if (mDeviceMode & ModeTlv::kModeRxOnWhenIdle)
             {
-                SendChildUpdateRequest();
-                mParentRequestTimer.Start(Timer::SecToMsec(mTimeout / kMaxChildKeepAliveAttempts));
+                if (mKeepAliveAttemptsSent >= kMaxChildKeepAliveAttempts)
+                {
+                    // Reattach when no Child Update Response received for more than kMaxChildKeepAliveAttempts
+                    BecomeDetached();
+                }
+                else
+                {
+                    SendChildUpdateRequest();
+                    mKeepAliveAttemptsSent++;
+                    mParentRequestTimer.Start(Timer::SecToMsec(mTimeout / kMaxChildKeepAliveAttempts));
+                }
             }
         }
         else
@@ -2927,6 +2937,7 @@ ThreadError Mle::HandleChildUpdateResponse(const Message &aMessage, const Ip6::M
         }
         else
         {
+            mKeepAliveAttemptsSent = 0;
             mNetif.GetMeshForwarder().SetRxOnWhenIdle(true);
         }
 
diff --git a/src/core/thread/mle.hpp b/src/core/thread/mle.hpp
index 614ac6e0c..54d1f868f 100644
--- a/src/core/thread/mle.hpp
+++ b/src/core/thread/mle.hpp
@@ -1419,6 +1419,7 @@ private:
     uint8_t mParentLinkQuality3;
     uint8_t mParentLinkQuality2;
     uint8_t mParentLinkQuality1;
+    uint8_t mKeepAliveAttemptsSent;
     LeaderDataTlv mParentLeaderData;
     bool mParentIsSingleton;