Sec.1.1 Historical Overview 3 Printer Multiplexer Central Front Printer processor end Terminal controller Multiplexer Figure 1.2 Network with one central processor but with shared communication links to devices. Personal computer Subnet erminal 鱼 CPU 曲型 CPU 出型 Figure 1.3 General network with a subnet of communication links and nodes.External devices are connected to the subnet via links to the subnet nodes.Sec. 1.1 Historical Overview 3 Central processor Figure 1.2 Network with one central processor but with shared communication links to devices. QI Subnet Personal computer Figure 1.3 General network with a subnet of communication links and nodes. External devices are connected to the subnet via links to the subnet nodes