diff --git a/src/JT808.DotNetty/Dtos/JT808ResultDto.cs b/src/JT808.DotNetty/Dtos/JT808ResultDto.cs
index da5cbf5..dabc8f2 100644
--- a/src/JT808.DotNetty/Dtos/JT808ResultDto.cs
+++ b/src/JT808.DotNetty/Dtos/JT808ResultDto.cs
@@ -18,6 +18,7 @@ namespace JT808.DotNetty.Dtos
         public const int Ok = 200;
         public const int Empty = 201;
         public const int NotFound = 404;
+        public const int Fail = 400;
         public const int Error = 500;
     }
 }
diff --git a/src/JT808.DotNetty/Internal/JT808UnificationSendServiceDefaultImpl.cs b/src/JT808.DotNetty/Internal/JT808UnificationSendServiceDefaultImpl.cs
index d6c8075..8c8581a 100644
--- a/src/JT808.DotNetty/Internal/JT808UnificationSendServiceDefaultImpl.cs
+++ b/src/JT808.DotNetty/Internal/JT808UnificationSendServiceDefaultImpl.cs
@@ -24,15 +24,24 @@ namespace JT808.DotNetty.Internal
                 var session = jT808SessionManager.GetSessionByTerminalPhoneNo(terminalPhoneNo);
                 if (session != null)
                 {
-                    session.Channel.WriteAndFlushAsync(Unpooled.WrappedBuffer(data));
-                    resultDto.Code = JT808ResultCode.Ok;
-                    resultDto.Data = true;
+                    if (session.Channel.Open)
+                    {
+                        session.Channel.WriteAndFlushAsync(Unpooled.WrappedBuffer(data));
+                        resultDto.Code = JT808ResultCode.Ok;
+                        resultDto.Data = true;
+                    }
+                    else
+                    {
+                        resultDto.Code = JT808ResultCode.Ok;
+                        resultDto.Data = false;
+                        resultDto.Message = "offline";
+                    }
                 }
                 else
                 {
                     resultDto.Code = JT808ResultCode.Ok;
                     resultDto.Data = false;
-                    resultDto.Message = "not session";
+                    resultDto.Message = "offline";
                 }
             }
             catch (Exception ex)
diff --git a/src/JT808.DotNetty/JT808SessionManager.cs b/src/JT808.DotNetty/JT808SessionManager.cs
index 49f812f..d2c9a50 100644
--- a/src/JT808.DotNetty/JT808SessionManager.cs
+++ b/src/JT808.DotNetty/JT808SessionManager.cs
@@ -121,7 +121,15 @@ namespace JT808.DotNetty
         public void TryAddOrUpdateSession(JT808Session appSession)
         {
             SessionIdDict.TryAdd(appSession.SessionID, appSession);
-            TerminalPhoneNo_SessionId_Dict.TryAdd(appSession.TerminalPhoneNo, appSession.SessionID);
+            if(TerminalPhoneNo_SessionId_Dict.TryAdd(appSession.TerminalPhoneNo, appSession.SessionID))
+            {
+                //使用场景：
+                //部标的超长待机设备,不会像正常的设备一样一直连着，可能10几分钟连上了，然后发完就关闭连接，
+                //这时候想下发数据需要知道设备什么时候上线，在这边做通知最好不过了。
+                //todo: 有设备关联上来可以进行通知
+                //todo: 使用Redis发布订阅
+                
+            }
         }
 
         public JT808Session RemoveSessionByID(string sessionID)
@@ -137,6 +145,9 @@ namespace JT808.DotNetty
                     {
                         TerminalPhoneNo_SessionId_Dict.TryRemove(key, out string sessionid);
                     }
+                    //todo: 设备离线可以进行通知
+                    //todo: 使用Redis 发布订阅
+
                     logger.LogInformation($">>>{sessionID}-{string.Join(",",removeKeys)} Session Remove.");
                     return session;
                 }