Configurable FastResend, CongestionWindow

kcp2k/Assets/kcp2k/MirrorTransport/KcpTransport.cs

@@ -16,6 +16,10 @@ public class KcpTransport : Transport
         [Tooltip("KCP internal update interval. 100ms is KCP default, but a lower interval is recommended to minimize latency and to scale to more networked entities.")]
         public uint Interval = 10;
         [Header("Advanced")]
+        [Tooltip("KCP fastresend parameter. Faster resend for the cost of higher bandwidth.")]
+        public int FastResend = 0;
+        [Tooltip("KCP congestion window can be disabled. This is necessary to Mirror 10k Benchmark. Disable this for high scale games if connections get chocked regularly.")]
+        public bool CongestionWindow = true; // KCP 'NoCongestionWindow' is false by default. here we negate it for ease of use.
         [Tooltip("KCP window size can be modified to support higher loads. For example, Mirror Benchmark requires 128 for 4k monsters, 512 for 10k monsters")]
         public uint SendWindowSize = 128; //Kcp.WND_SND; 32 by default. 128 is better for 4k Benchmark etc.
         [Tooltip("KCP window size can be modified to support higher loads. For example, Mirror Benchmark requires 128 for 4k monsters, 512 for 10k monsters")]
@@ -44,6 +48,8 @@ void Awake()
                 (connectionId) => OnServerDisconnected.Invoke(connectionId),
                 NoDelay,
                 Interval,
+                FastResend,
+                CongestionWindow,
                 SendWindowSize,
                 ReceiveWindowSize
             );
@@ -58,7 +64,7 @@ public override bool Available() =>
         public override bool ClientConnected() => client.connected;
         public override void ClientConnect(string address)
         {
-            client.Connect(address, Port, NoDelay, Interval, SendWindowSize, ReceiveWindowSize);
+            client.Connect(address, Port, NoDelay, Interval, FastResend, CongestionWindow, SendWindowSize, ReceiveWindowSize);
         }
         public override bool ClientSend(int channelId, ArraySegment<byte> segment)
         {

kcp2k/Assets/kcp2k/highlevel/KcpClient.cs

@@ -23,7 +23,7 @@ public KcpClient(Action OnConnected, Action<ArraySegment<byte>> OnData, Action O
             this.OnDisconnected = OnDisconnected;
         }
 
-        public void Connect(string address, ushort port, bool noDelay, uint interval, uint SendWindowSize = Kcp.WND_SND, uint ReceiveWindowSize = Kcp.WND_RCV)
+        public void Connect(string address, ushort port, bool noDelay, uint interval, int fastResend = 0, bool congestionWindow = true, uint SendWindowSize = Kcp.WND_SND, uint ReceiveWindowSize = Kcp.WND_RCV)
         {
             if (connected)
             {
@@ -54,7 +54,7 @@ public void Connect(string address, ushort port, bool noDelay, uint interval, ui
             };
 
             // connect
-            connection.Connect(address, port, noDelay, interval, SendWindowSize, ReceiveWindowSize);
+            connection.Connect(address, port, noDelay, interval, fastResend, congestionWindow, SendWindowSize, ReceiveWindowSize);
         }
 
         public void Send(ArraySegment<byte> segment)

kcp2k/Assets/kcp2k/highlevel/KcpClientConnection.cs

@@ -8,7 +8,7 @@ public class KcpClientConnection : KcpConnection
     {
         readonly byte[] buffer = new byte[1500];
 
-        public void Connect(string host, ushort port, bool noDelay, uint interval = Kcp.INTERVAL, uint SendWindowSize = Kcp.WND_SND, uint ReceiveWindowSize = Kcp.WND_RCV)
+        public void Connect(string host, ushort port, bool noDelay, uint interval = Kcp.INTERVAL, int fastResend = 0, bool congestionWindow = true, uint SendWindowSize = Kcp.WND_SND, uint ReceiveWindowSize = Kcp.WND_RCV)
         {
             Debug.Log($"KcpClient: connect to {host}:{port}");
             IPAddress[] ipAddress = Dns.GetHostAddresses(host);
@@ -18,7 +18,7 @@ public void Connect(string host, ushort port, bool noDelay, uint interval = Kcp.
             remoteEndpoint = new IPEndPoint(ipAddress[0], port);
             socket = new Socket(remoteEndpoint.AddressFamily, SocketType.Dgram, ProtocolType.Udp);
             socket.Connect(remoteEndpoint);
-            SetupKcp(noDelay, interval, SendWindowSize, ReceiveWindowSize);
+            SetupKcp(noDelay, interval, fastResend, congestionWindow, SendWindowSize, ReceiveWindowSize);
 
             // client should send handshake to server as very first message
             SendHandshake();

kcp2k/Assets/kcp2k/highlevel/KcpConnection.cs

@@ -59,10 +59,12 @@ public abstract class KcpConnection
 
         // NoDelay, interval, window size are the most important configurations.
         // let's force require the parameters so we don't forget it anywhere.
-        protected void SetupKcp(bool noDelay, uint interval = Kcp.INTERVAL, uint SendWindowSize = Kcp.WND_SND, uint ReceiveWindowSize = Kcp.WND_RCV)
+        protected void SetupKcp(bool noDelay, uint interval = Kcp.INTERVAL, int fastResend = 0, bool congestionWindow = true, uint SendWindowSize = Kcp.WND_SND, uint ReceiveWindowSize = Kcp.WND_RCV)
         {
             kcp = new Kcp(0, RawSend);
-            kcp.SetNoDelay(noDelay ? 1u : 0u, interval);
+            // set nodelay.
+            // note that kcp uses 'nocwnd' internally so we negate the parameter
+            kcp.SetNoDelay(noDelay ? 1u : 0u, interval, fastResend, !congestionWindow);
             kcp.SetWindowSize(SendWindowSize, ReceiveWindowSize);
             refTime.Start();
             state = KcpState.Connected;

kcp2k/Assets/kcp2k/highlevel/KcpServer.cs

@@ -23,6 +23,13 @@ public class KcpServer
         // interval is recommended to minimize latency and to scale to more
         // networked entities.
         public uint Interval;
+        // KCP fastresend parameter. Faster resend for the cost of higher
+        // bandwidth.
+        public int FastResend;
+        // KCP 'NoCongestionWindow' is false by default. here we negate it for
+        // ease of use. This can be disabled for high scale games if connections
+        // choke regularly.
+        public bool CongestionWindow;
         // KCP window size can be modified to support higher loads.
         // for example, Mirror Benchmark requires:
         //   128, 128 for 4k monsters
@@ -44,6 +51,8 @@ public KcpServer(Action<int> OnConnected,
                          Action<int> OnDisconnected,
                          bool NoDelay,
                          uint Interval,
+                         int FastResend = 0,
+                         bool CongestionWindow = true,
                          uint SendWindowSize = Kcp.WND_SND,
                          uint ReceiveWindowSize = Kcp.WND_RCV)
         {
@@ -52,6 +61,8 @@ public KcpServer(Action<int> OnConnected,
             this.OnDisconnected = OnDisconnected;
             this.NoDelay = NoDelay;
             this.Interval = Interval;
+            this.FastResend = FastResend;
+            this.CongestionWindow = CongestionWindow;
             this.SendWindowSize = SendWindowSize;
             this.ReceiveWindowSize = ReceiveWindowSize;
         }
@@ -111,7 +122,7 @@ public void Tick()
                 if (!connections.TryGetValue(connectionId, out KcpServerConnection connection))
                 {
                     // create a new KcpConnection
-                    connection = new KcpServerConnection(socket, newClientEP, NoDelay, Interval, SendWindowSize, ReceiveWindowSize);
+                    connection = new KcpServerConnection(socket, newClientEP, NoDelay, Interval, FastResend, CongestionWindow, SendWindowSize, ReceiveWindowSize);
 
                     // DO NOT add to connections yet. only if the first message
                     // is actually the kcp handshake. otherwise it's either:

kcp2k/Assets/kcp2k/highlevel/KcpServerConnection.cs

@@ -5,11 +5,11 @@ namespace kcp2k
 {
     public class KcpServerConnection : KcpConnection
     {
-        public KcpServerConnection(Socket socket, EndPoint remoteEndpoint, bool noDelay, uint interval = Kcp.INTERVAL, uint SendWindowSize = Kcp.WND_SND, uint ReceiveWindowSize = Kcp.WND_RCV)
+        public KcpServerConnection(Socket socket, EndPoint remoteEndpoint, bool noDelay, uint interval = Kcp.INTERVAL, int fastResend = 0, bool congestionWindow = true, uint SendWindowSize = Kcp.WND_SND, uint ReceiveWindowSize = Kcp.WND_RCV)
         {
             this.socket = socket;
             this.remoteEndpoint = remoteEndpoint;
-            SetupKcp(noDelay, interval, SendWindowSize, ReceiveWindowSize);
+            SetupKcp(noDelay, interval, fastResend, congestionWindow, SendWindowSize, ReceiveWindowSize);
         }
 
         protected override void RawSend(byte[] data, int length)