diff --git a/etc/emqx.conf b/etc/emqx.conf
index 3604f2efd..ea90b8d28 100644
--- a/etc/emqx.conf
+++ b/etc/emqx.conf
@@ -591,10 +591,10 @@ zone.external.enable_stats = on
 ## zone.external.server_keepalive = 0
 
 ## The backoff for MQTT keepalive timeout. The broker will kick a connection out
-## until 'Keepalive * backoff * 2' timeout.
+## until 'Keepalive * backoff' timeout.
 ##
 ## Value: Float > 0.5
-zone.external.keepalive_backoff = 0.75
+zone.external.keepalive_backoff = 1.5
 
 ## Maximum number of subscriptions allowed, 0 means no limit.
 ##
diff --git a/priv/emqx.schema b/priv/emqx.schema
index a8ed316c2..77167b440 100644
--- a/priv/emqx.schema
+++ b/priv/emqx.schema
@@ -748,7 +748,7 @@ end}.
 
 %% @doc Keepalive backoff
 {mapping, "zone.$name.keepalive_backoff", "emqx.zones", [
-  {default, 0.75},
+  {default, 1.5},
   {datatype, float}
 ]}.
 
diff --git a/src/emqx_connection.erl b/src/emqx_connection.erl
index a7f71d9aa..139011891 100644
--- a/src/emqx_connection.erl
+++ b/src/emqx_connection.erl
@@ -45,7 +45,8 @@
           rate_limit,
           publish_limit,
           limit_timer,
-          idle_timeout
+          idle_timeout,
+          last_packet_ts = 0
          }).
 
 -define(SOCK_STATS, [recv_oct, recv_cnt, send_oct, send_cnt, send_pend]).
@@ -243,23 +244,17 @@ handle_info({inet_reply, _Sock, ok}, State) ->
 handle_info({inet_reply, _Sock, {error, Reason}}, State) ->
     shutdown(Reason, State);
 
-handle_info({keepalive, start, Interval}, State = #state{transport = Transport, socket = Socket}) ->
+handle_info({keepalive, start, Interval}, State) ->
     ?LOG(debug, "Keepalive at the interval of ~p", [Interval], State),
-    StatFun = fun() ->
-                case Transport:getstat(Socket, [recv_oct]) of
-                    {ok, [{recv_oct, RecvOct}]} -> {ok, RecvOct};
-                    Error                       -> Error
-                end
-             end,
-    case emqx_keepalive:start(StatFun, Interval, {keepalive, check}) of
+    case emqx_keepalive:start(Interval, {keepalive, check}) of
         {ok, KeepAlive} ->
             {noreply, State#state{keepalive = KeepAlive}};
         {error, Error} ->
             shutdown(Error, State)
     end;
 
-handle_info({keepalive, check}, State = #state{keepalive = KeepAlive}) ->
-    case emqx_keepalive:check(KeepAlive) of
+handle_info({keepalive, check}, State = #state{keepalive = KeepAlive, last_packet_ts = LastPacketTs}) ->
+    case emqx_keepalive:check(KeepAlive, LastPacketTs) of
         {ok, KeepAlive1} ->
             {noreply, State#state{keepalive = KeepAlive1}};
         {error, timeout} ->
@@ -296,14 +291,14 @@ code_change(_OldVsn, State, _Extra) ->
 
 %% Receive and parse data
 handle_packet(<<>>, State) ->
-    {noreply, maybe_gc(ensure_stats_timer(ensure_rate_limit(State)))};
+    {noreply, maybe_gc(ensure_stats_timer(ensure_rate_limit(State#state{last_packet_ts = erlang:system_time(millisecond)})))};
 
 handle_packet(Data, State = #state{proto_state  = ProtoState,
                                    parser_state = ParserState,
                                    idle_timeout = IdleTimeout}) ->
     case catch emqx_frame:parse(Data, ParserState) of
         {more, NewParserState} ->
-            {noreply, run_socket(State#state{parser_state = NewParserState}), IdleTimeout};
+            {noreply, State#state{parser_state = NewParserState, last_packet_ts = erlang:system_time(millisecond)}, IdleTimeout};
         {ok, Packet = ?PACKET(Type), Rest} ->
             emqx_metrics:received(Packet),
             case emqx_protocol:received(Packet, ProtoState) of
diff --git a/src/emqx_keepalive.erl b/src/emqx_keepalive.erl
index 25740b099..59dbe73b9 100644
--- a/src/emqx_keepalive.erl
+++ b/src/emqx_keepalive.erl
@@ -14,51 +14,37 @@
 
 -module(emqx_keepalive).
 
--export([start/3, check/1, cancel/1]).
+-export([start/2, check/2, cancel/1]).
 
--record(keepalive, {statfun, statval, tsec, tmsg, tref, repeat = 0}).
+-record(keepalive, {tmsec, tmsg, tref}).
 
 -type(keepalive() :: #keepalive{}).
 
 -export_type([keepalive/0]).
 
+-define(SWEET_SPOT, 50).    % 50ms
+
 %% @doc Start a keepalive
--spec(start(fun(), integer(), any()) -> {ok, keepalive()} | {error, term()}).
-start(_, 0, _) ->
+-spec(start(integer(), any()) -> {ok, keepalive()}).
+start(0, _) ->
     {ok, #keepalive{}};
-start(StatFun, TimeoutSec, TimeoutMsg) ->
-    case catch StatFun() of
-        {ok, StatVal} ->
-            {ok, #keepalive{statfun = StatFun, statval = StatVal,
-                            tsec = TimeoutSec, tmsg = TimeoutMsg,
-                            tref = timer(TimeoutSec, TimeoutMsg)}};
-        {error, Error} ->
-            {error, Error};
-        {'EXIT', Reason} ->
-            {error, Reason}
-    end.
+start(TimeoutSec, TimeoutMsg) ->
+    {ok, #keepalive{tmsec = TimeoutSec * 1000, tmsg = TimeoutMsg, tref = timer(TimeoutSec * 1000 + ?SWEET_SPOT, TimeoutMsg)}}.
 
 %% @doc Check keepalive, called when timeout...
--spec(check(keepalive()) -> {ok, keepalive()} | {error, term()}).
-check(KeepAlive = #keepalive{statfun = StatFun, statval = LastVal, repeat = Repeat}) ->
-    case catch StatFun() of
-        {ok, NewVal} ->
-            if NewVal =/= LastVal ->
-                    {ok, resume(KeepAlive#keepalive{statval = NewVal, repeat = 0})};
-                Repeat < 1 ->
-                    {ok, resume(KeepAlive#keepalive{statval = NewVal, repeat = Repeat + 1})};
-                true ->
-                    {error, timeout}
-            end;
-        {error, Error} ->
-            {error, Error};
-        {'EXIT', Reason} ->
-            {error, Reason}
+-spec(check(keepalive(), integer()) -> {ok, keepalive()} | {error, term()}).
+check(KeepAlive = #keepalive{tmsec = TimeoutMs}, LastPacketTs) ->
+    TimeDiff = erlang:system_time(millisecond) - LastPacketTs,
+    case TimeDiff >= TimeoutMs of
+        true ->
+            {error, timeout};
+        false ->
+            {ok, resume(KeepAlive, TimeoutMs + ?SWEET_SPOT - TimeDiff)}
     end.
 
--spec(resume(keepalive()) -> keepalive()).
-resume(KeepAlive = #keepalive{tsec = TimeoutSec, tmsg = TimeoutMsg}) ->
-    KeepAlive#keepalive{tref = timer(TimeoutSec, TimeoutMsg)}.
+-spec(resume(keepalive(), integer()) -> keepalive()).
+resume(KeepAlive = #keepalive{tmsg = TimeoutMsg}, TimeoutMs) ->
+    KeepAlive#keepalive{tref = timer(TimeoutMs, TimeoutMsg)}.
 
 %% @doc Cancel Keepalive
 -spec(cancel(keepalive()) -> ok).
@@ -67,6 +53,6 @@ cancel(#keepalive{tref = TRef}) when is_reference(TRef) ->
 cancel(_) ->
     ok.
 
-timer(Secs, Msg) ->
-    erlang:send_after(timer:seconds(Secs), self(), Msg).
+timer(Millisecond, Msg) ->
+    erlang:send_after(Millisecond, self(), Msg).
 
diff --git a/src/emqx_protocol.erl b/src/emqx_protocol.erl
index 8301cf014..9d548f066 100644
--- a/src/emqx_protocol.erl
+++ b/src/emqx_protocol.erl
@@ -607,7 +607,7 @@ check_proto_ver(#mqtt_packet_connect{proto_ver  = Ver,
                                      proto_name = Name}, _PState) ->
     case lists:member({Ver, Name}, ?PROTOCOL_NAMES) of
         true  -> ok;
-        false -> {error, ?RC_PROTOCOL_ERROR}
+        false -> {error, ?RC_UNSUPPORTED_PROTOCOL_VERSION}
     end.
 
 %% MQTT3.1 does not allow null clientId
diff --git a/src/emqx_ws_connection.erl b/src/emqx_ws_connection.erl
index fa08fa1bb..3a2d4fdae 100644
--- a/src/emqx_ws_connection.erl
+++ b/src/emqx_ws_connection.erl
@@ -40,7 +40,8 @@
           keepalive,
           enable_stats,
           stats_timer,
-          shutdown
+          shutdown,
+          last_packet_ts = 0
          }).
 
 -define(SOCK_STATS, [recv_oct, recv_cnt, send_oct, send_cnt]).
@@ -152,13 +153,10 @@ send_fun(WsPid) ->
         WsPid ! {binary, iolist_to_binary(Data)}
     end.
 
-stat_fun() ->
-    fun() -> {ok, get(recv_oct)} end.
-
 websocket_handle({binary, <<>>}, State) ->
-    {ok, ensure_stats_timer(State)};
+    {ok, ensure_stats_timer(State#state{last_packet_ts = erlang:system_time(millisecond)})};
 websocket_handle({binary, [<<>>]}, State) ->
-    {ok, ensure_stats_timer(State)};
+    {ok, ensure_stats_timer(State#state{last_packet_ts = erlang:system_time(millisecond)})};
 websocket_handle({binary, Data}, State = #state{parser_state = ParserState,
                                                 proto_state  = ProtoState}) ->
     BinSize = iolist_size(Data),
@@ -167,7 +165,7 @@ websocket_handle({binary, Data}, State = #state{parser_state = ParserState,
     emqx_metrics:inc('bytes/received', BinSize),
     case catch emqx_frame:parse(iolist_to_binary(Data), ParserState) of
         {more, NewParserState} ->
-            {ok, State#state{parser_state = NewParserState}};
+            {ok, State#state{parser_state = NewParserState, last_packet_ts = erlang:system_time(millisecond)}};
         {ok, Packet, Rest} ->
             emqx_metrics:received(Packet),
             put(recv_cnt, get(recv_cnt) + 1),
@@ -225,7 +223,7 @@ websocket_info({timeout, Timer, emit_stats},
 
 websocket_info({keepalive, start, Interval}, State) ->
     ?WSLOG(debug, "Keepalive at the interval of ~p", [Interval], State),
-    case emqx_keepalive:start(stat_fun(), Interval, {keepalive, check}) of
+    case emqx_keepalive:start(Interval, {keepalive, check}) of
         {ok, KeepAlive} ->
             {ok, State#state{keepalive = KeepAlive}};
         {error, Error} ->
@@ -233,8 +231,8 @@ websocket_info({keepalive, start, Interval}, State) ->
             shutdown(Error, State)
     end;
 
-websocket_info({keepalive, check}, State = #state{keepalive = KeepAlive}) ->
-    case emqx_keepalive:check(KeepAlive) of
+websocket_info({keepalive, check}, State = #state{keepalive = KeepAlive, last_packet_ts = LastPacketTs}) ->
+    case emqx_keepalive:check(KeepAlive, LastPacketTs) of
         {ok, KeepAlive1} ->
             {ok, State#state{keepalive = KeepAlive1}};
         {error, timeout} ->