Socket s = new Socket(AddressFamily.InterNetwork,SocketType.Stream,ProtocolType.Tcp);
IPEndPoint endp = new IPEndPoint(IPAddress.Any,ポート番号);
s.Bind(endp);
s.Listen(10);
Socket mySocket = s.Accept();
byte[] bytes = new byte[1024];
mySocket.Receive(bytes);
string tx = Encoding.Default.GetString(bytes);
mySocket.Close();

Socket s = new Socket(AddressFamily.InterNetwork,SocketType.Stream,ProtocolType.Tcp);
IPEndPoint endp = new IPEndPoint(Dns.Resolve("ホスト名").AddressList[0],ポート番号);
s.Connect(endp);
s.Send(Encoding.Default.GetBytes("送信メッセージ"));
s.Close();