爲什麼我能夠通過藍牙4.2發送超過明顯的最大數據量？

Question

My research showed（請參閱第5頁）可通過藍牙4.2發送的最大數據量爲257字節。

但是，我能夠在我的Python腳本和Java應用程序之間發送990個字節。爲什麼我能發送這麼多的數據？我發現有關最大數據錯誤的信息，還是發生了其他事情？

的Python藍牙腳本：

 #Parameters config 
     sdr=RtlSdr() 
     sdr.fc=100e6 
     sdr.gain=48 
     sdr.rs=1.024e6 

     #Bluetooth connection 

     server_sock=BluetoothSocket(RFCOMM) 
     server_sock.bind(("",PORT_ANY)) 
     server_sock.listen(1) 

     port=server_sock.getsockname()[1] 
     uuid="94f39d29-7d6d-437d-973b-fba39e49d4ee" 
     client_sock,client_info=server_sock.accept() 
while (1): 
     samples= sdr.read_samples(256*1024) 
     result=psd(samples, NFFT=70, Fc=sdr.fc/1e6, Fs=sdr.rs/1e6) 
     tab_freq=(result[1]) 
     value_freq=str(tab_freq)[1:-1] 
     value_freq2=[format(float(v),".4f")[:6] for v in value_freq.split()] 
     value_freq3="\n".join(value_pxx2) 

     #SAME FOR POWER VALUE 
     #THEN I SEND DATA BY BLUETOOTH 

     client_sock.send(value_freq3) 

的Java藍牙代碼：

private class ThreadConnected extends Thread { 
     private final BluetoothSocket connectedBluetoothSocket; 
     private final InputStream connectedInputStream; 
     private final OutputStream connectedOutputStream; 

     boolean running; 

     public ThreadConnected(BluetoothSocket socket) { 
      connectedBluetoothSocket = socket; 
      InputStream in = null; 
      OutputStream out = null; 
      running = true; 
      try { 
       in = socket.getInputStream(); 
       out = socket.getOutputStream(); 
      } catch (IOException e) { 
       // TODO Auto-generated catch block 
       e.printStackTrace(); 
      } 

      connectedInputStream = in; 
      connectedOutputStream = out; 
     } 

     @Override 
     public void run() { 
      byte[] buffer = new byte[1048576]; // 20 bits 
      int bytes; 
      String strRx = ""; 

      while (running) { 
       try { 
        bytes = connectedInputStream.read(buffer); 
        final String strReceived_freq = new String(buffer,0, bytes/2); 
        final String strReceived_pxx = new String(buffer,(bytes/2)+1, bytes); 
        //final int samples_sdr=new Integer(buffer,0,bytes); 
        final String strByteCnt = String.valueOf(bytes) + " bytes received.\n"; 

        runOnUiThread(new Runnable(){ 

         @Override 
         public void run() { 
           Pxx_value.setText(strReceived_pxx+"\n"); // get data PXX 
           freq_value.setText(strReceived_freq+"\n"); // get data freq 

          // plot value 
          /* for (int i=0; i<nb_points; i++) 
          { 
           freq[i]=Double.parseDouble(strReceived_freq); 
           pxx[i]=Double.parseDouble(strReceived_pxx); 
           series.appendData(new DataPoint(freq[i],pxx[i]), true,500); 
          }*/ 

         }}); 

       } catch (IOException e) { 
        // TODO Auto-generated catch block 
        e.printStackTrace(); 
        cancel(); 

        final String msgConnectionLost = "Connection lost:\n" + e.getMessage(); 
        runOnUiThread(new Runnable(){ 

         @Override 
         public void run() { 

         }}); 
       } 
      } 
     } 

     public void write(byte[] buffer) { 
      try { 
       connectedOutputStream.write(buffer); 
      } catch (IOException e) { 
       // TODO Auto-generated catch block 
       e.printStackTrace(); 
      } 
     } 

     public void cancel() { 
      running = false; 
      try { 
       connectedBluetoothSocket.close(); 
      } catch (IOException e) { 
       // TODO Auto-generated catch block 
       e.printStackTrace(); 
      } 
     } 
    } 

Answer 1

您鏈接到顯示文檔的LE（低能量）鏈路層數據包格式，如規定第6卷，B部分，藍牙核心規範第2.1節。

您正在使用RFCOMM，它是Bluetooth Classic（又名BR/EDR）配置文件。 BR/EDR的鏈路層數據包格式在第2卷B部分的第6節中指定，並且顯示有效載荷長達2790字節。

在任何情況下，您使用的API都不允許您訪問鏈接層。你正在寫一個RFCOMM通道（它被設計成或多或少像串口一樣工作），你可以根據需要寫入儘可能多的字節。您的庫和底層平臺將負責將您的數據放入適當數量的L2CAP數據包中，然後將這些數據包進一步封裝在鏈路層數據包中。您將遇到的主要限制是實現中的緩衝區大小。在這種情況下，基於套接字的API會將調用中寫入的字節數返回到send，您將能夠稍後嘗試重新傳輸。