[[UIDevice currentDevice] setProximityMonitoringEnabled:YES];

    AVAudioSession *audioSession = [AVAudioSession sharedInstance];

    //默认情况下扬声器播放

    [audioSession setCategory:AVAudioSessionCategoryPlayback withOptions:AVAudioSessionCategoryOptionMixWithOthers error:nil];

    [audioSession setActive:YES error:nil];

计算机网络自顶向下第三章传输层二TCP