计算机网络涉及计算机和通信两个领域。在传统的有线局域网（ＬＡＮ）中，计算机等设备被网络连线紧紧牵制着而无法实现可移动的通信，更无法发挥便携式计算机的通信功能。近些年来，随着局域网的应用领域不断拓宽和现代通信方式的不断变化，尤其是移动和便携式通信的发展，无 Computer network involves two areas of computer and communications. In a traditional wired local area network (LAN), computers and other devices are tightly bound by the network connection and can not be achieved mobile communication, but also can not play the communication function of a portable computer. In recent years, with the constant expansion of the field of application of the local area network and the continuous changes of modern communication methods, especially the development of mobile and portable communication, none