1、引用以下幾個單元

     IdBaseComponent, IdComponent, IdRawBase,  IdRawClient, IdIcmpClient;

2、函式模組

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        功能： 檢查網路是否正常連通   

        引數： 無

        返回值： 成功： True   失敗： False

       2014年3月22日  編寫

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function CheckOnLine: Boolean;
const
  Url = 'www.sina.com'; //廣東電信測速 0.08s
var
  aIdICMPClient: TIdICMPClient;
begin
  Result := False;
  aIdICMPClient := TIdIcmpClient.Create(nil);
  try 
    aIdICMPClient.ReceiveTimeout := 1000; //1500ms is timeout
    aIdICMPClient.Host := Url;
    try
      aIdICMPClient.Ping();
      if (aIdICMPClient.ReplyStatus.FromIpAddress <> '0.0.0.0') and
         (aIdICMPClient.ReplyStatus.FromIpAddress <> '') and
         (aIdICMPClient.ReplyStatus.BytesReceived > 0) then  //有收到資料
        Result := True;
    except
      Result := False;
    end;
  finally
    aIdICMPClient.Free;
  end;
end;