diff --git a/tcpip/transport/tcp/connect.go b/tcpip/transport/tcp/connect.go
index 1eb46a7..6864608 100644
--- a/tcpip/transport/tcp/connect.go
+++ b/tcpip/transport/tcp/connect.go
@@ -772,9 +772,48 @@ func (e *endpoint) handleSegments() *tcpip.Error {
 		e.snd.sendAck()
 	}
 
+	// TODO keepalive 解决 ZWP 问题
+	e.resetKeepaliveTimer(true)
+
 	return nil
 }
 
+func (e *endpoint) keepaliveTimerExpired() *tcpip.Error {
+	return nil
+}
+
+// NOTE 这里是 Nagle algorithm 的实现 也就是用来解决 发送端的 ZWP 问题
+func (e *endpoint) resetKeepaliveTimer(receivedData bool) *tcpip.Error {
+	e.keepalive.Lock()
+	defer e.keepalive.Unlock()
+	if receivedData {
+		e.keepalive.unacked = 0
+		logger.NOTICE("测试 keepalive 有数据进入")
+	} else {
+		logger.NOTICE("测试 keepalive 无数据进入")
+	}
+
+	if e.keepalive.unacked >= e.keepalive.count {
+		e.keepalive.Unlock()
+		return tcpip.ErrConnectionReset
+	}
+
+	// RFC1122 4.2.3.6: TCP keepalive is a dataless ACK with
+	// seg.seq = snd.nxt-1.
+	e.keepalive.unacked++
+	e.keepalive.Unlock()
+	e.snd.sendSegment(buffer.VectorisedView{}, flagAck, e.snd.sndNxt-1)
+	e.resetKeepaliveTimer(false)
+	return nil
+}
+
+// disableKeepaliveTimer stops the keepalive timer.
+func (e *endpoint) disableKeepaliveTimer() {
+	e.keepalive.Lock()
+	e.keepalive.timer.disable()
+	e.keepalive.Unlock()
+}
+
 // protocolMainLoop 是TCP协议的主循环。它在自己的goroutine中运行，负责握手、发送段和处理收到的段
 func (e *endpoint) protocolMainLoop(handshake bool) *tcpip.Error {
 
@@ -826,6 +865,9 @@ func (e *endpoint) protocolMainLoop(handshake bool) *tcpip.Error {
 		e.rcvListMu.Unlock()
 	}
 
+	e.keepalive.timer.init(&e.keepalive.waker)
+	defer e.keepalive.timer.cleanup()
+
 	e.mu.Lock()
 	e.state = stateConnected
 	// TODO drained
@@ -863,6 +905,10 @@ func (e *endpoint) protocolMainLoop(handshake bool) *tcpip.Error {
 				return nil
 			},
 		},
+		{
+			w: &e.keepalive.waker,
+			f: e.keepaliveTimerExpired,
+		},
 		{
 			// NOTE 这段代码的设计值得借鉴
 			w: &e.notificationWaker,
diff --git a/tcpip/transport/tcp/endpoint.go b/tcpip/transport/tcp/endpoint.go
index 170e0a5..e6a04a1 100644
--- a/tcpip/transport/tcp/endpoint.go
+++ b/tcpip/transport/tcp/endpoint.go
@@ -57,6 +57,21 @@ type SACKInfo struct {
 	NumBlocks int
 }
 
+// keepalive is a synchronization wrapper used to appease stateify. See the
+// comment in endpoint, where it is used.
+//
+// +stateify savable
+type keepalive struct {
+	sync.Mutex
+	enabled  bool
+	idle     time.Duration
+	interval time.Duration
+	count    int
+	unacked  int
+	timer    timer
+	waker    sleep.Waker
+}
+
 // endpoint 表示TCP端点。该结构用作端点用户和协议实现之间的接口;让并发goroutine调用端点是合法的，
 // 它们是正确同步的。然而，协议实现在单个goroutine中运行。
 type endpoint struct {
@@ -170,6 +185,8 @@ type endpoint struct {
 	// read by Accept() calls.
 	acceptedChan chan *endpoint
 
+	keepalive keepalive
+
 	// The following are only used from the protocol goroutine, and
 	// therefore don't need locks to protect them.
 	rcv *receiver
@@ -192,6 +209,12 @@ func newEndpoint(stack *stack.Stack, netProto tcpip.NetworkProtocolNumber, waite
 		rcvBufSize:  DefaultBufferSize,
 		sndBufSize:  DefaultBufferSize,
 		sndMTU:      int(math.MaxInt32),
+		keepalive: keepalive{
+			// Linux defaults.
+			idle:     2 * time.Hour,
+			interval: 75 * time.Second,
+			count:    9,
+		},
 	}
 
 	var ss SendBufferSizeOption
diff --git a/tcpip/transport/tcp/rcv.go b/tcpip/transport/tcp/rcv.go
index c46d96c..c2c89ca 100644
--- a/tcpip/transport/tcp/rcv.go
+++ b/tcpip/transport/tcp/rcv.go
@@ -71,6 +71,7 @@ func (r *receiver) nonZeroWindow() {
 		return
 	}
 	logger.NOTICE("探测到 0 窗口")
+	// FIXME 揭开注释
 	//time.Sleep(100 * time.Second)
 	//r.ep.snd.sendAck()
 }
diff --git a/tcpip/transport/tcp/snd.go b/tcpip/transport/tcp/snd.go
index e15e43b..70c6473 100644
--- a/tcpip/transport/tcp/snd.go
+++ b/tcpip/transport/tcp/snd.go
@@ -537,12 +537,11 @@ func (s *sender) sendData() {
 		// NOTE 开启计时器 如果在RTO后没有回信(snd.handleRecvdSegment 中有数据可以处理) 那么将会重发
 		// 在 s.resendTimer.init() 中 将会调用 Assert() 唤醒重发函数 retransmitTimerExpired()
 		s.resendTimer.enable(s.rto)
-		logger.NOTICE("没数据 所以开启一个定时器")
 	}
 
 	// TODO KEEPALIVE
 	if s.sndUna == s.sndNxt {
-		//log.Fatal("注意测试", s.sndWnd)
+		s.ep.resetKeepaliveTimer(false)
 	}
 
 	time.Sleep(20 * time.Millisecond)