X25 Devices and Protocol Operation

X.25 network devices fall into three general categories: data terminal equipment (DTE), data circuit-terminating equipment (DCE), and packet-switching exchange (PSE). Data terminal equipment devices are end systems that communicate across the X.25 network. They are usually terminals, person al computers, or network hosts, and are located on the premises of individual subscribers. DCE devices are communications devices, such as modems and packet switches, tltat provide the interface between [DTE devices and a PSE, and are generally located in the cameo' s facilisies. PSEs are switches that compose the bulk of the carrier's network. They transfer data from one DTE device to another through the X.25 PSN. Figure 17-1 illustrates thc relationships among the three types of X.25 network devices.

Figure 17-1. DTEs, DCEs, and PSEs Make Up an X.25 Network

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Figure 17-1. DTEs, DCEs, and PSEs Make Up an X.25 Network

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