diff --git a/src/Orleans.SignalR/Clients/ClientGrain.cs b/src/Orleans.SignalR/Clients/ClientGrain.cs
index 6e847d5..d5497fd 100644
--- a/src/Orleans.SignalR/Clients/ClientGrain.cs
+++ b/src/Orleans.SignalR/Clients/ClientGrain.cs
@@ -2,7 +2,7 @@
 using Microsoft.Extensions.Logging;
 using Orleans.Concurrency;
 using Orleans.Providers;
-using Orleans.SignalR.Core;
+using Orleans.SignalR.Connections;
 using Orleans.Streams;
 using System;
 using System.Collections.Generic;
diff --git a/src/Orleans.SignalR/Core/ConnectionGrain.cs b/src/Orleans.SignalR/Connections/ConnectionGrain.cs
similarity index 93%
rename from src/Orleans.SignalR/Core/ConnectionGrain.cs
rename to src/Orleans.SignalR/Connections/ConnectionGrain.cs
index f3e03f9..d2e3ad4 100644
--- a/src/Orleans.SignalR/Core/ConnectionGrain.cs
+++ b/src/Orleans.SignalR/Connections/ConnectionGrain.cs
@@ -1,17 +1,15 @@
-using System.Buffers;
-using System.Collections.Generic;
-using System.Linq;
-using System.Threading.Tasks;
-using Microsoft.AspNetCore.SignalR.Protocol;
+using Microsoft.AspNetCore.SignalR.Protocol;
 using Microsoft.Extensions.Logging;
-using Orleans;
 using Orleans.Concurrency;
 using Orleans.Streams;
+using System.Buffers;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
 
-namespace Orleans.SignalR.Core
+namespace Orleans.SignalR.Connections
 {
-    internal abstract class ConnectionGrain<TGrainState> : Grain<TGrainState>, IConnectionGrain
-        where TGrainState : ConnectionState, new()
+    internal class ConnectionGrain : Grain<ConnectionState>, IConnectionGrain
     {
         private readonly ILogger _logger;
         private IStreamProvider _streamProvider;
@@ -19,7 +17,7 @@ internal abstract class ConnectionGrain<TGrainState> : Grain<TGrainState>, IConn
 
         protected ConnectionGrainKey KeyData;
 
-        internal ConnectionGrain(ILogger logger)
+        public ConnectionGrain(ILogger<ConnectionGrain> logger)
         {
             _logger = logger;
         }
diff --git a/src/Orleans.SignalR/Core/ConnectionGrainKey.cs b/src/Orleans.SignalR/Connections/ConnectionGrainKey.cs
similarity index 94%
rename from src/Orleans.SignalR/Core/ConnectionGrainKey.cs
rename to src/Orleans.SignalR/Connections/ConnectionGrainKey.cs
index b36c242..4b98818 100644
--- a/src/Orleans.SignalR/Core/ConnectionGrainKey.cs
+++ b/src/Orleans.SignalR/Connections/ConnectionGrainKey.cs
@@ -1,6 +1,6 @@
 using System.Diagnostics;
 
-namespace Orleans.SignalR.Core
+namespace Orleans.SignalR.Connections
 {
     [DebuggerDisplay("{DebuggerDisplay,nq}")]
     internal struct ConnectionGrainKey
diff --git a/src/Orleans.SignalR/Core/IConnectionGrain.cs b/src/Orleans.SignalR/Connections/IConnectionGrain.cs
similarity index 92%
rename from src/Orleans.SignalR/Core/IConnectionGrain.cs
rename to src/Orleans.SignalR/Connections/IConnectionGrain.cs
index 3361274..a587141 100644
--- a/src/Orleans.SignalR/Core/IConnectionGrain.cs
+++ b/src/Orleans.SignalR/Connections/IConnectionGrain.cs
@@ -1,8 +1,8 @@
-using System.Collections.Generic;
+using Orleans.SignalR.Core;
+using System.Collections.Generic;
 using System.Threading.Tasks;
-using Orleans;
 
-namespace Orleans.SignalR.Core
+namespace Orleans.SignalR.Connections
 {
     /// <summary>
     /// Grain interface Grouped of connections, such as user or custom group.
diff --git a/src/Orleans.SignalR/Core/GrainExtensions.cs b/src/Orleans.SignalR/Core/GrainExtensions.cs
index aed8e03..568219d 100644
--- a/src/Orleans.SignalR/Core/GrainExtensions.cs
+++ b/src/Orleans.SignalR/Core/GrainExtensions.cs
@@ -1,6 +1,7 @@
 using Microsoft.AspNetCore.SignalR.Protocol;
 using Orleans.Concurrency;
 using Orleans.SignalR.Clients;
+using Orleans.SignalR.Connections;
 using Orleans.SignalR.Core;
 using Orleans.SignalR.Groups;
 using Orleans.SignalR.Users;
@@ -55,12 +56,12 @@ public static void SendOneWay(this IHubMessageInvoker grain, string methodName,
             grain.InvokeOneWay(g => g.Send(methodName, args));
         }
 
-        [Obsolete("Use Send instead", false)]
-        public static async Task SendSignalRMessage(this IConnectionGrain grain, string methodName, params object[] message)
-        {
-            var invocationMessage = new InvocationMessage(methodName, message).AsImmutable();
-            await grain.Send(invocationMessage);
-        }
+        //[Obsolete("Use Send instead", false)]
+        //public static async Task SendSignalRMessage(this IConnectionGrain grain, string methodName, params object[] message)
+        //{
+        //    var invocationMessage = new InvocationMessage(methodName, message).AsImmutable();
+        //    await grain.Send(invocationMessage);
+        //}
 
         /// <summary>
         /// Invokes a method on the hub.
diff --git a/src/Orleans.SignalR/Groups/GroupGrain.cs b/src/Orleans.SignalR/Groups/GroupGrain.cs
index dd79f20..aa13da6 100644
--- a/src/Orleans.SignalR/Groups/GroupGrain.cs
+++ b/src/Orleans.SignalR/Groups/GroupGrain.cs
@@ -1,20 +1,125 @@
+using Microsoft.AspNetCore.SignalR.Protocol;
 using Microsoft.Extensions.Logging;
 using Orleans.Concurrency;
 using Orleans.Providers;
-using Orleans.SignalR.Core;
+using Orleans.SignalR.Connections;
+using Orleans.Streams;
+using System.Buffers;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
 
 namespace Orleans.SignalR.Groups
 {
     [StorageProvider(ProviderName = SignalrConstants.STORAGE_PROVIDER)]
     [Reentrant]
-    internal class GroupGrain : ConnectionGrain<GroupState>, IGroupGrain
+    internal class GroupGrain : Grain<GroupState>, IGroupGrain
     {
-        public GroupGrain(ILogger<GroupGrain> logger) : base(logger)
+        private readonly ILogger _logger;
+        private IStreamProvider _streamProvider;
+        private Dictionary<string, StreamSubscriptionHandle<string>> _connectionStreamHandles;
+
+        protected ConnectionGrainKey KeyData;
+
+        public GroupGrain(ILogger<GroupGrain> logger)
+        {
+            _logger = logger;
+        }
+
+        public override async Task OnActivateAsync()
+        {
+            KeyData = new ConnectionGrainKey(this.GetPrimaryKeyString());
+            _connectionStreamHandles = new Dictionary<string, StreamSubscriptionHandle<string>>();
+            _streamProvider = GetStreamProvider(SignalrConstants.STREAM_PROVIDER);
+            var subscriptionTasks = new List<Task>();
+            foreach (var connection in State.Connections)
+            {
+                var clientDisconnectStream = _streamProvider.GetStream<string>(SignalrConstants.CLIENT_DISCONNECT_STREAM_ID, connection);
+                var subscriptions = await clientDisconnectStream.GetAllSubscriptionHandles();
+                foreach (var subscription in subscriptions)
+                {
+                    subscriptionTasks.Add(subscription.ResumeAsync(async (connectionId, _) => await Remove(connectionId)));
+                }
+            }
+            await Task.WhenAll(subscriptionTasks);
+        }
+
+        public virtual async Task Add(string connectionId)
         {
+            var shouldWriteState = State.Connections.Add(connectionId);
+            if (!_connectionStreamHandles.ContainsKey(connectionId))
+            {
+                var clientDisconnectStream = _streamProvider.GetStream<string>(SignalrConstants.CLIENT_DISCONNECT_STREAM_ID, connectionId);
+                var subscription = await clientDisconnectStream.SubscribeAsync(async (connId, _) => await Remove(connId));
+                _connectionStreamHandles[connectionId] = subscription;
+            }
+
+            if (shouldWriteState)
+                await WriteStateAsync();
+        }
+
+        public virtual async Task Remove(string connectionId)
+        {
+            var shouldWriteState = State.Connections.Remove(connectionId);
+            if (_connectionStreamHandles.TryGetValue(connectionId, out var stream))
+            {
+                await stream.UnsubscribeAsync();
+                _connectionStreamHandles.Remove(connectionId);
+            }
+
+            if (State.Connections.Count == 0)
+            {
+                await ClearStateAsync();
+                DeactivateOnIdle();
+            }
+            else if (shouldWriteState)
+            {
+                await WriteStateAsync();
+            }
+        }
+
+        public virtual Task Send(Immutable<InvocationMessage> message)
+        {
+            return SendAll(message, State.Connections);
+        }
+
+        public Task SendExcept(string methodName, object[] args, IReadOnlyList<string> excludedConnectionIds)
+        {
+            var message = new Immutable<InvocationMessage>(new InvocationMessage(methodName, args));
+            return SendAll(message, State.Connections.Where(x => !excludedConnectionIds.Contains(x)).ToList());
+        }
+
+        public Task<int> Count()
+        {
+            return Task.FromResult(State.Connections.Count);
+        }
+
+        protected Task SendAll(Immutable<InvocationMessage> message, IReadOnlyCollection<string> connections)
+        {
+            _logger.LogDebug("Sending message to {hubName}.{targetMethod} on group {groupId} to {connectionsCount} connection(s)",
+                KeyData.HubName, message.Value.Target, KeyData.Id, connections.Count);
+
+            var tasks = ArrayPool<Task>.Shared.Rent(connections.Count);
+            try
+            {
+                int index = 0;
+                foreach (var connection in connections)
+                {
+                    var client = GrainFactory.GetClientGrain(KeyData.HubName, connection);
+                    tasks[index++] = client.Send(message);
+                }
+
+                return Task.WhenAll(tasks.Where(x => x != null).ToArray());
+            }
+            finally
+            {
+                ArrayPool<Task>.Shared.Return(tasks);
+            }
         }
     }
 
-    internal class GroupState : ConnectionState
+    internal class GroupState
     {
+        public HashSet<string> Connections { get; set; } = new HashSet<string>();
     }
 }
\ No newline at end of file
diff --git a/src/Orleans.SignalR/Groups/IGroupGrain.cs b/src/Orleans.SignalR/Groups/IGroupGrain.cs
index 2906bc4..a0b0d32 100644
--- a/src/Orleans.SignalR/Groups/IGroupGrain.cs
+++ b/src/Orleans.SignalR/Groups/IGroupGrain.cs
@@ -1,8 +1,37 @@
 using Orleans.SignalR.Core;
+using System.Collections.Generic;
+using System.Threading.Tasks;
 
 namespace Orleans.SignalR.Groups
 {
-    public interface IGroupGrain : IConnectionGrain
+    /// <summary>
+    /// Grain interface Grouped of connections, such as user or custom group.
+    /// </summary>
+    public interface IGroupGrain : IHubMessageInvoker, IGrainWithStringKey
     {
+        /// <summary>
+        /// Add connection id to the group.
+        /// </summary>
+        /// <param name="connectionId">Connection id to add.</param>
+        Task Add(string connectionId);
+
+        /// <summary>
+        /// Remove the connection id to the group.
+        /// </summary>
+        /// <param name="connectionId">Connection id to remove.</param>
+        Task Remove(string connectionId);
+
+        /// <summary>
+        /// Gets the connection count in the group.
+        /// </summary>
+        Task<int> Count();
+
+        /// <summary>
+        /// Invokes a method on the hub except the specified connection ids.
+        /// </summary>
+        /// <param name="methodName">Target method name to invoke.</param>
+        /// <param name="args">Arguments to pass to the target method.</param>
+        /// <param name="excludedConnectionIds">Connection ids to exclude.</param>
+        Task SendExcept(string methodName, object[] args, IReadOnlyList<string> excludedConnectionIds);
     }
 }
\ No newline at end of file
diff --git a/src/Orleans.SignalR/Orleans.SignalR.csproj b/src/Orleans.SignalR/Orleans.SignalR.csproj
index 7477588..e3f924c 100644
--- a/src/Orleans.SignalR/Orleans.SignalR.csproj
+++ b/src/Orleans.SignalR/Orleans.SignalR.csproj
@@ -20,6 +20,11 @@
 		<RepositoryUrl>https://github.com/zeus82/Orleans.SignalR.git</RepositoryUrl>
 	</PropertyGroup>
 
+	<ItemGroup>
+	  <Compile Remove="Connections\ConnectionGrain.cs" />
+	  <Compile Remove="Connections\IConnectionGrain.cs" />
+	</ItemGroup>
+
 	<ItemGroup>
 		<!-- see https://gist.github.com/tebeco/a6e0d9a3885a0a36e702795219bd4fe9 -->
 		<FrameworkReference Include="Microsoft.AspNetCore.App" />
diff --git a/src/Orleans.SignalR/Users/IUserGrain.cs b/src/Orleans.SignalR/Users/IUserGrain.cs
index 3fbfc6c..d38fe96 100644
--- a/src/Orleans.SignalR/Users/IUserGrain.cs
+++ b/src/Orleans.SignalR/Users/IUserGrain.cs
@@ -1,8 +1,37 @@
 using Orleans.SignalR.Core;
+using System.Collections.Generic;
+using System.Threading.Tasks;
 
 namespace Orleans.SignalR.Users
 {
-    public interface IUserGrain : IConnectionGrain
+    /// <summary>
+    /// Grain interface Grouped of connections, such as user or custom group.
+    /// </summary>
+    public interface IUserGrain : IHubMessageInvoker, IGrainWithStringKey
     {
+        /// <summary>
+        /// Add connection id to the group.
+        /// </summary>
+        /// <param name="connectionId">Connection id to add.</param>
+        Task Add(string connectionId);
+
+        /// <summary>
+        /// Remove the connection id to the group.
+        /// </summary>
+        /// <param name="connectionId">Connection id to remove.</param>
+        Task Remove(string connectionId);
+
+        /// <summary>
+        /// Gets the connection count in the group.
+        /// </summary>
+        Task<int> Count();
+
+        /// <summary>
+        /// Invokes a method on the hub except the specified connection ids.
+        /// </summary>
+        /// <param name="methodName">Target method name to invoke.</param>
+        /// <param name="args">Arguments to pass to the target method.</param>
+        /// <param name="excludedConnectionIds">Connection ids to exclude.</param>
+        Task SendExcept(string methodName, object[] args, IReadOnlyList<string> excludedConnectionIds);
     }
 }
\ No newline at end of file
diff --git a/src/Orleans.SignalR/Users/UserGrain.cs b/src/Orleans.SignalR/Users/UserGrain.cs
index 3b583de..54ab2ec 100644
--- a/src/Orleans.SignalR/Users/UserGrain.cs
+++ b/src/Orleans.SignalR/Users/UserGrain.cs
@@ -1,20 +1,125 @@
-using Microsoft.Extensions.Logging;
+using Microsoft.AspNetCore.SignalR.Protocol;
+using Microsoft.Extensions.Logging;
 using Orleans.Concurrency;
 using Orleans.Providers;
-using Orleans.SignalR.Core;
+using Orleans.SignalR.Connections;
+using Orleans.Streams;
+using System.Buffers;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading.Tasks;
 
 namespace Orleans.SignalR.Users
 {
     [StorageProvider(ProviderName = SignalrConstants.STORAGE_PROVIDER)]
     [Reentrant]
-    internal class UserGrain : ConnectionGrain<UserState>, IUserGrain
+    internal class UserGrain : Grain<UserState>, IUserGrain
     {
-        public UserGrain(ILogger<UserGrain> logger) : base(logger)
+        private readonly ILogger _logger;
+        private IStreamProvider _streamProvider;
+        private Dictionary<string, StreamSubscriptionHandle<string>> _connectionStreamHandles;
+
+        protected ConnectionGrainKey KeyData;
+
+        public UserGrain(ILogger<UserGrain> logger)
+        {
+            _logger = logger;
+        }
+
+        public override async Task OnActivateAsync()
+        {
+            KeyData = new ConnectionGrainKey(this.GetPrimaryKeyString());
+            _connectionStreamHandles = new Dictionary<string, StreamSubscriptionHandle<string>>();
+            _streamProvider = GetStreamProvider(SignalrConstants.STREAM_PROVIDER);
+            var subscriptionTasks = new List<Task>();
+            foreach (var connection in State.Connections)
+            {
+                var clientDisconnectStream = _streamProvider.GetStream<string>(SignalrConstants.CLIENT_DISCONNECT_STREAM_ID, connection);
+                var subscriptions = await clientDisconnectStream.GetAllSubscriptionHandles();
+                foreach (var subscription in subscriptions)
+                {
+                    subscriptionTasks.Add(subscription.ResumeAsync(async (connectionId, _) => await Remove(connectionId)));
+                }
+            }
+            await Task.WhenAll(subscriptionTasks);
+        }
+
+        public virtual async Task Add(string connectionId)
         {
+            var shouldWriteState = State.Connections.Add(connectionId);
+            if (!_connectionStreamHandles.ContainsKey(connectionId))
+            {
+                var clientDisconnectStream = _streamProvider.GetStream<string>(SignalrConstants.CLIENT_DISCONNECT_STREAM_ID, connectionId);
+                var subscription = await clientDisconnectStream.SubscribeAsync(async (connId, _) => await Remove(connId));
+                _connectionStreamHandles[connectionId] = subscription;
+            }
+
+            if (shouldWriteState)
+                await WriteStateAsync();
+        }
+
+        public virtual async Task Remove(string connectionId)
+        {
+            var shouldWriteState = State.Connections.Remove(connectionId);
+            if (_connectionStreamHandles.TryGetValue(connectionId, out var stream))
+            {
+                await stream.UnsubscribeAsync();
+                _connectionStreamHandles.Remove(connectionId);
+            }
+
+            if (State.Connections.Count == 0)
+            {
+                await ClearStateAsync();
+                DeactivateOnIdle();
+            }
+            else if (shouldWriteState)
+            {
+                await WriteStateAsync();
+            }
+        }
+
+        public virtual Task Send(Immutable<InvocationMessage> message)
+        {
+            return SendAll(message, State.Connections);
+        }
+
+        public Task SendExcept(string methodName, object[] args, IReadOnlyList<string> excludedConnectionIds)
+        {
+            var message = new Immutable<InvocationMessage>(new InvocationMessage(methodName, args));
+            return SendAll(message, State.Connections.Where(x => !excludedConnectionIds.Contains(x)).ToList());
+        }
+
+        public Task<int> Count()
+        {
+            return Task.FromResult(State.Connections.Count);
+        }
+
+        protected Task SendAll(Immutable<InvocationMessage> message, IReadOnlyCollection<string> connections)
+        {
+            _logger.LogDebug("Sending message to {hubName}.{targetMethod} on group {groupId} to {connectionsCount} connection(s)",
+                KeyData.HubName, message.Value.Target, KeyData.Id, connections.Count);
+
+            var tasks = ArrayPool<Task>.Shared.Rent(connections.Count);
+            try
+            {
+                int index = 0;
+                foreach (var connection in connections)
+                {
+                    var client = GrainFactory.GetClientGrain(KeyData.HubName, connection);
+                    tasks[index++] = client.Send(message);
+                }
+
+                return Task.WhenAll(tasks.Where(x => x != null).ToArray());
+            }
+            finally
+            {
+                ArrayPool<Task>.Shared.Return(tasks);
+            }
         }
     }
 
-    internal class UserState : ConnectionState
+    internal class UserState
     {
+        public HashSet<string> Connections { get; set; } = new HashSet<string>();
     }
 }
\ No newline at end of file