tcp-streams.cs

var endpoint = new IPEndPoint( IPAddress.Loopback, 6000 );
var server = new Socket( AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp );
server.SetSocketOption( SocketOptionLevel.Tcp, SocketOptionName.KeepAlive, true );
server.SetSocketOption( SocketOptionLevel.Tcp, SocketOptionName.TcpKeepAliveTime, 90 );
server.SetSocketOption( SocketOptionLevel.Tcp, SocketOptionName.TcpKeepAliveInterval, 5 );
server.SetSocketOption( SocketOptionLevel.Tcp, SocketOptionName.TcpKeepAliveRetryCount, 3 );
server.Bind( endpoint );
server.Listen( 1 );
Task.Run( ( ) =>
{
    var client = server.Accept( );
    Task.Run( ( ) =>
    {
        while( true )
        {
            client.Send( Encoding.UTF8.GetBytes( "hell from server to client" ) );
            Thread.Sleep( 1000 );
        }
    } );
    Task.Run( ( ) =>
    {
        while( true )
        {
            var bytes = new byte[ 20 ];
            client.Receive( bytes );
            Console.WriteLine( Encoding.UTF8.GetString( bytes ) );
        }
    } );
} );
var clientSocket = new Socket( AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp );
Task.Run( ( ) =>
{
    clientSocket.Connect( endpoint );
    Task.Run( ( ) =>
    {
        while( true )
        {
            clientSocket.Send( Encoding.UTF8.GetBytes( "hell from client to server" ) );
            Thread.Sleep( 2000 );
        }
    } );
    Task.Run( ( ) =>
    {
        while( true )
        {
            var bytes = new byte[ 20 ];
            clientSocket.Receive( bytes );
            Console.WriteLine( Encoding.UTF8.GetString( bytes ) );
        }
    } );
} );

using TCP keepalive