diff --git a/source/NetCoreServer/FileCache.cs b/source/NetCoreServer/FileCache.cs
index c84943f..76736f1 100644
--- a/source/NetCoreServer/FileCache.cs
+++ b/source/NetCoreServer/FileCache.cs
@@ -95,7 +95,7 @@ public bool Remove(string key)
         /// <returns>'true' if the cache path was setup, 'false' if failed to setup the cache path</returns>
         public bool InsertPath(string path, string prefix = "/", string filter = "*.*", TimeSpan timeout = new TimeSpan(), InsertHandler handler = null)
         {
-            handler ??= (FileCache cache, string key, byte[] value, TimeSpan timespan) => cache.Add(key, value, timespan);
+            handler = handler ?? ((FileCache cache, string key, byte[] value, TimeSpan timespan) => cache.Add(key, value, timespan));
 
             // Try to find and remove the previous path
             RemovePathInternal(path);
diff --git a/source/NetCoreServer/HttpClient.cs b/source/NetCoreServer/HttpClient.cs
index 29e827a..98b69c4 100644
--- a/source/NetCoreServer/HttpClient.cs
+++ b/source/NetCoreServer/HttpClient.cs
@@ -259,7 +259,7 @@ public HttpClientEx(IPEndPoint endpoint) : base(endpoint) {}
         /// <returns>HTTP request Task</returns>
         public Task<HttpResponse> SendRequest(HttpRequest request, TimeSpan? timeout = null)
         {
-            timeout ??= TimeSpan.FromMinutes(1);
+            timeout = timeout ?? TimeSpan.FromMinutes(1);
 
             _tcs = new TaskCompletionSource<HttpResponse>();
             Request = request;
diff --git a/source/NetCoreServer/HttpServer.cs b/source/NetCoreServer/HttpServer.cs
index 419f04c..363aea3 100644
--- a/source/NetCoreServer/HttpServer.cs
+++ b/source/NetCoreServer/HttpServer.cs
@@ -47,7 +47,7 @@ public class HttpServer : TcpServer
         /// <param name="timeout">Refresh cache timeout (default is 1 hour)</param>
         public void AddStaticContent(string path, string prefix = "/", string filter = "*.*", TimeSpan? timeout = null)
         {
-            timeout ??= TimeSpan.FromHours(1);
+            timeout = timeout ?? TimeSpan.FromHours(1);
 
             bool Handler(FileCache cache, string key, byte[] value, TimeSpan timespan)
             {
diff --git a/source/NetCoreServer/HttpsClient.cs b/source/NetCoreServer/HttpsClient.cs
index 2ba4006..c8bb203 100644
--- a/source/NetCoreServer/HttpsClient.cs
+++ b/source/NetCoreServer/HttpsClient.cs
@@ -268,7 +268,7 @@ public HttpsClientEx(SslContext context, IPEndPoint endpoint) : base(context, en
         /// <returns>HTTP request Task</returns>
         public Task<HttpResponse> SendRequest(HttpRequest request, TimeSpan? timeout = null)
         {
-            timeout ??= TimeSpan.FromMinutes(1);
+            timeout = timeout ?? TimeSpan.FromMinutes(1);
 
             _tcs = new TaskCompletionSource<HttpResponse>();
             Request = request;
diff --git a/source/NetCoreServer/HttpsServer.cs b/source/NetCoreServer/HttpsServer.cs
index c7eee72..020be81 100644
--- a/source/NetCoreServer/HttpsServer.cs
+++ b/source/NetCoreServer/HttpsServer.cs
@@ -51,7 +51,7 @@ public class HttpsServer : SslServer
         /// <param name="timeout">Refresh cache timeout (default is 1 hour)</param>
         public void AddStaticContent(string path, string prefix = "/", string filter = "*.*", TimeSpan? timeout = null)
         {
-            timeout ??= TimeSpan.FromHours(1);
+            timeout = timeout ?? TimeSpan.FromHours(1);
 
             bool Handler(FileCache cache, string key, byte[] value, TimeSpan timespan)
             {
diff --git a/source/NetCoreServer/NetCoreServer.csproj b/source/NetCoreServer/NetCoreServer.csproj
index a712960..fbfc3ac 100644
--- a/source/NetCoreServer/NetCoreServer.csproj
+++ b/source/NetCoreServer/NetCoreServer.csproj
@@ -1,15 +1,18 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net8.0</TargetFramework>
     <Version>8.0.7.0</Version>
-    <Authors>Ivan Shynkarenka</Authors>
-    <Copyright>Copyright (c) 2019-2023 Ivan Shynkarenka</Copyright>
-    <RepositoryUrl>https://github.com/chronoxor/NetCoreServer</RepositoryUrl>
-    <Description>Ultra fast and low latency asynchronous socket server &amp; client C# .NET Core library with support TCP, SSL, UDP, HTTP, HTTPS, WebSocket protocols and 10K connections problem solution</Description>
+    <AssemblyName>GoPlay.NetCoreServer</AssemblyName>
+    <Authors>Jennal</Authors>
+    <Copyright>Copyright © What2d Ltd. 2023</Copyright>
+    <RepositoryUrl>https://github.com/jennal/NetCoreServer</RepositoryUrl>
+    <Description>Fork from [https://github.com/chronoxor/NetCoreServer](https://github.com/chronoxor/NetCoreServer), make it support .NET Standard 2.1
+
+Ultra fast and low latency asynchronous socket server &amp; client C# .NET Core library with support TCP, SSL, UDP, HTTP, HTTPS, WebSocket protocols and 10K connections problem solution</Description>
     <PackageLicenseExpression>MIT</PackageLicenseExpression>
-    <PackageProjectUrl>https://github.com/chronoxor/NetCoreServer</PackageProjectUrl>
+    <PackageProjectUrl>https://github.com/jennal/NetCoreServer</PackageProjectUrl>
     <PackageTags>async;client;server;tcp;udp;ssl;tls;http;https;websocket;low latency;performance</PackageTags>
+    <TargetFrameworks>net6.0;net7.0;net8.0;net9.0;netstandard2.1</TargetFrameworks>
   </PropertyGroup>
 
   <PropertyGroup>
diff --git a/source/NetCoreServer/SslClient.cs b/source/NetCoreServer/SslClient.cs
index 7f8a509..1e6d183 100644
--- a/source/NetCoreServer/SslClient.cs
+++ b/source/NetCoreServer/SslClient.cs
@@ -265,12 +265,14 @@ public virtual bool Connect()
             // Apply the option: keep alive
             if (OptionKeepAlive)
                 Socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.KeepAlive, true);
+#if NET6_0_OR_GREATER
             if (OptionTcpKeepAliveTime >= 0)
                 Socket.SetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.TcpKeepAliveTime, OptionTcpKeepAliveTime);
             if (OptionTcpKeepAliveInterval >= 0)
                 Socket.SetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.TcpKeepAliveInterval, OptionTcpKeepAliveInterval);
             if (OptionTcpKeepAliveRetryCount >= 0)
                 Socket.SetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.TcpKeepAliveRetryCount, OptionTcpKeepAliveRetryCount);
+#endif
             // Apply the option: no delay
             if (OptionNoDelay)
                 Socket.SetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.NoDelay, true);
@@ -840,12 +842,14 @@ private void ProcessConnect(SocketAsyncEventArgs e)
                 // Apply the option: keep alive
                 if (OptionKeepAlive)
                     Socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.KeepAlive, true);
+#if NET6_0_OR_GREATER
                 if (OptionTcpKeepAliveTime >= 0)
                     Socket.SetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.TcpKeepAliveTime, OptionTcpKeepAliveTime);
                 if (OptionTcpKeepAliveInterval >= 0)
                     Socket.SetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.TcpKeepAliveInterval, OptionTcpKeepAliveInterval);
                 if (OptionTcpKeepAliveRetryCount >= 0)
                     Socket.SetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.TcpKeepAliveRetryCount, OptionTcpKeepAliveRetryCount);
+#endif
                 // Apply the option: no delay
                 if (OptionNoDelay)
                     Socket.SetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.NoDelay, true);
diff --git a/source/NetCoreServer/SslContext.cs b/source/NetCoreServer/SslContext.cs
index d9450fb..a793b8f 100644
--- a/source/NetCoreServer/SslContext.cs
+++ b/source/NetCoreServer/SslContext.cs
@@ -12,7 +12,13 @@ public class SslContext
         /// <summary>
         /// Initialize SSL context with default protocols
         /// </summary>
-        public SslContext() : this(SslProtocols.Tls13) {}
+        public SslContext() : this(
+#if NET6_0_OR_GREATER
+            SslProtocols.Tls13
+#else
+            SslProtocols.Tls12
+#endif
+        ) {}
         /// <summary>
         /// Initialize SSL context with given protocols
         /// </summary>
diff --git a/source/NetCoreServer/SslSession.cs b/source/NetCoreServer/SslSession.cs
index 4a22cb9..1305e35 100644
--- a/source/NetCoreServer/SslSession.cs
+++ b/source/NetCoreServer/SslSession.cs
@@ -106,12 +106,14 @@ internal void Connect(Socket socket)
             // Apply the option: keep alive
             if (Server.OptionKeepAlive)
                 Socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.KeepAlive, true);
+#if NET6_0_OR_GREATER
             if (Server.OptionTcpKeepAliveTime >= 0)
                 Socket.SetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.TcpKeepAliveTime, Server.OptionTcpKeepAliveTime);
             if (Server.OptionTcpKeepAliveInterval >= 0)
                 Socket.SetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.TcpKeepAliveInterval, Server.OptionTcpKeepAliveInterval);
             if (Server.OptionTcpKeepAliveRetryCount >= 0)
                 Socket.SetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.TcpKeepAliveRetryCount, Server.OptionTcpKeepAliveRetryCount);
+#endif
             // Apply the option: no delay
             if (Server.OptionNoDelay)
                 Socket.SetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.NoDelay, true);
diff --git a/source/NetCoreServer/TcpClient.cs b/source/NetCoreServer/TcpClient.cs
index feb0df8..24e140f 100644
--- a/source/NetCoreServer/TcpClient.cs
+++ b/source/NetCoreServer/TcpClient.cs
@@ -250,12 +250,14 @@ public virtual bool Connect()
             // Apply the option: keep alive
             if (OptionKeepAlive)
                 Socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.KeepAlive, true);
+#if NET6_0_OR_GREATER
             if (OptionTcpKeepAliveTime >= 0)
                 Socket.SetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.TcpKeepAliveTime, OptionTcpKeepAliveTime);
             if (OptionTcpKeepAliveInterval >= 0)
                 Socket.SetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.TcpKeepAliveInterval, OptionTcpKeepAliveInterval);
             if (OptionTcpKeepAliveRetryCount >= 0)
                 Socket.SetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.TcpKeepAliveRetryCount, OptionTcpKeepAliveRetryCount);
+#endif
             // Apply the option: no delay
             if (OptionNoDelay)
                 Socket.SetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.NoDelay, true);
@@ -791,12 +793,14 @@ private void ProcessConnect(SocketAsyncEventArgs e)
                 // Apply the option: keep alive
                 if (OptionKeepAlive)
                     Socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.KeepAlive, true);
+#if NET6_0_OR_GREATER
                 if (OptionTcpKeepAliveTime >= 0)
                     Socket.SetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.TcpKeepAliveTime, OptionTcpKeepAliveTime);
                 if (OptionTcpKeepAliveInterval >= 0)
                     Socket.SetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.TcpKeepAliveInterval, OptionTcpKeepAliveInterval);
                 if (OptionTcpKeepAliveRetryCount >= 0)
                     Socket.SetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.TcpKeepAliveRetryCount, OptionTcpKeepAliveRetryCount);
+#endif                
                 // Apply the option: no delay
                 if (OptionNoDelay)
                     Socket.SetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.NoDelay, true);
diff --git a/source/NetCoreServer/TcpSession.cs b/source/NetCoreServer/TcpSession.cs
index 7ae9e1b..442ca36 100644
--- a/source/NetCoreServer/TcpSession.cs
+++ b/source/NetCoreServer/TcpSession.cs
@@ -103,12 +103,14 @@ internal void Connect(Socket socket)
             // Apply the option: keep alive
             if (Server.OptionKeepAlive)
                 Socket.SetSocketOption(SocketOptionLevel.Socket, SocketOptionName.KeepAlive, true);
+#if NET6_0_OR_GREATER
             if (Server.OptionTcpKeepAliveTime >= 0)
                 Socket.SetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.TcpKeepAliveTime, Server.OptionTcpKeepAliveTime);
             if (Server.OptionTcpKeepAliveInterval >= 0)
                 Socket.SetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.TcpKeepAliveInterval, Server.OptionTcpKeepAliveInterval);
             if (Server.OptionTcpKeepAliveRetryCount >= 0)
                 Socket.SetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.TcpKeepAliveRetryCount, Server.OptionTcpKeepAliveRetryCount);
+#endif
             // Apply the option: no delay
             if (Server.OptionNoDelay)
                 Socket.SetSocketOption(SocketOptionLevel.Tcp, SocketOptionName.NoDelay, true);
diff --git a/source/NetCoreServer/UdpClient.cs b/source/NetCoreServer/UdpClient.cs
index dcfb339..92b182a 100644
--- a/source/NetCoreServer/UdpClient.cs
+++ b/source/NetCoreServer/UdpClient.cs
@@ -457,7 +457,11 @@ public virtual long Send(EndPoint endpoint, ReadOnlySpan<byte> buffer)
             try
             {
                 // Sent datagram to the server
+#if NET6_0_OR_GREATER
                 long sent = Socket.SendTo(buffer, SocketFlags.None, endpoint);
+#else
+                long sent = Socket.SendTo(buffer.ToArray(), SocketFlags.None, endpoint);
+#endif
                 if (sent > 0)
                 {
                     // Update statistic
diff --git a/source/NetCoreServer/UdpServer.cs b/source/NetCoreServer/UdpServer.cs
index 183b9ef..0c40ca9 100644
--- a/source/NetCoreServer/UdpServer.cs
+++ b/source/NetCoreServer/UdpServer.cs
@@ -473,7 +473,11 @@ public virtual long Send(EndPoint endpoint, ReadOnlySpan<byte> buffer)
             try
             {
                 // Sent datagram to the client
+#if NET6_0_OR_GREATER
                 long sent = Socket.SendTo(buffer, SocketFlags.None, endpoint);
+#else
+                long sent = Socket.SendTo(buffer.ToArray(), SocketFlags.None, endpoint);
+#endif
                 if (sent > 0)
                 {
                     // Update statistic