一、引言微型机局部网络的通信按工作性质可分为二个自然层次,物理介质层和面向数据通信功能层。前者对应于网络协议的物理级,它通过硬设备和物理链路将主机系统实际接到网络上,这是通信的物理基础。后者由链路级、网络级和传输级三级协议构成,这就是本文讨论的网络通信软件。本层的主要任务是提供网中不同主机上进程一进程之间通信的手段,这是实现不同主机上的实体之间通信的基础。为了完成这一任务,网络通信软件必须具备以下主 I. INTRODUCTION According to the nature of work, the communication of local network of microcomputers can be divided into two natural layers, the physical medium layer and the data communication functional layer. The former corresponds to the physical level of the network protocol, which physically connects the host system to the network through hard devices and physical links, which is the physical basis for communications. The latter by the link-level, network-level and transport level three-level protocol constitutes, this is the network communication software discussed in this article. The main task of this layer is to provide a means of communication between processes on different hosts in the network, which is the basis for communication between entities on different hosts. In order to accomplish this task, the network communication software must have the following master