Delphi 7 中使用IdUDPServer1和IdUDPClient1控件实现通信检测

Delphi 7 中使用IdUDPServer1和IdUDPClient1控件实现通信，可是如何检测两台电脑已经连通了？代码怎么写啊？求大神

D7确实经典，但已经落伍了，用xe版本吧

udp发送这个东西不检测是否通不通，用TCP连接可以检测；
实在想用可以在server发送一个字符串，client接受到以后，反馈一个什么的字符串，表示正常通讯了

在Client端：
   procedure TUDPMainForm.SendButtonClick(Sender: TObject);
var
   MessageID: Integer;
   ThisMessage: String;
   ReceivedString: String;
begin
   MessageID := Random(MAXINT);
   ThisMessage := 'Message: ' + IntToStr(MessageID);
   UDPMemo.Lines.Add('Sending ' + ThisMessage);
   UDPClient.Send(ThisMessage);
   ReceivedString := UDPClient.ReceiveString();   //该方法取得由服务端返回的信息。
   if ReceivedString = '' then
     UDPMemo.Lines.Add('No response received from the server after ' + IntToStr(UDPClient.ReceiveTimeout) + ' millseconds.')
   else
     UDPMemo.Lines.Add('Received: ' + ReceivedString)
end;

Server端：

procedure TUDPMainForm.UDPServerUDPRead(Sender: TObject; AData: TStream; ABinding: TIdSocketHandle);
var
   DataStringStream: TStringStream;
   s: String;
begin
   DataStringStream := TStringStream.Create('');
   try
     DataStringStream.CopyFrom(AData, AData.Size);
     UDPMemo.Lines.Add('Received "' + DataStringStream.DataString + '" from ' + ABinding.PeerIP + ' on port ' + IntToStr(ABinding.PeerPort));
     s := 'Replied from ' + UDPServer.LocalName + ' to "' + DataStringStream.DataString + '"';
     ABinding.SendTo(ABinding.PeerIP, ABinding.PeerPort, s[1], Length(s));
   finally
     DataStringStream.Free;
   end;