今天,网络面临着前所未有的挑战。上网的用户越来越多,他们所要访问的站点也越来越多。桌面计算机的能力继续快速提高,并推动了消耗大量带宽的实时的桌面应用的发展。对于其它一些新应用,特别是多媒体应用,原有的网络基础结构由于在最初设计时并未考虑 Today, the Internet faces unprecedented challenges. Internet users more and more, they want to visit more and more sites. The power of desktop computers continues to grow rapidly, driving the development of real-time desktop applications that consume large amounts of bandwidth. For some other new applications, especially for multimedia applications, the original network infrastructure was not considered in the original design