讲述分组交换的概念，优缺点，和其他交换方式的比较，是数据通信方面的好ppt-The document gives the concept of packet switching, longcoming and shortcoming. And also give a compare with other techs. It s a good material about data communication.

实现QQ程序的抽屉效果，即QQ好友分组切换效果-QQ procedures to achieve drawer effect that packet switching effect of QQ friends ......