为什么要学习计算机网络 20世纪出现了计算机，计算机与通信技术的结合并且大发展，出现了计算机网络，出现了Internet；它是20世纪最伟大的科技成就之一。 -Why study computer network appeared in the 20th century, computer, the combination of computer and communication technologies and large-scale development, there have