how to increase TCP window size in android for FTP?

Question

I am trying to develop a simple ftp client using open source ftp4j library for android. I wanted to know if there is any way I can change/increase the tcp window size for data transfer. I have tried changing the receive buffer size on data socket, but when I checked the Wireshark logs the window size was not changing at all, it stays around 195232.

    protected Socket tcpConnectForDataTransferChannel(String host, int port) throws IOException {
    Socket socket = new Socket();
    int size = (1024*1024);
    socket.setSoTimeout(readTimeout * 1000);
    socket.setSoLinger(true, closeTimeout);
    socket.setReceiveBufferSize(size);
    socket.setSendBufferSize(size);
    socket.connect(new InetSocketAddress(host, port), connectionTimeout * 1000);
    Log.d(TAG,String.valueOf(socket.getReceiveBufferSize()));
    return socket;
}

Thanks

Answer 1

You've done it. Setting the receive buffer size determines the maximum receive window. But the platform is free to adjust up the size requested up or down. Check it after you set it to see what value the kernel gave you.

195232 is a pretty decent size. There's no advantage to making it any larger than the bandwidth-delay product.