X.75 is an International Telecommunication Union (ITU) standard specifying the interface for interconnecting two X.25 networks. X.75 is almost identical to X.25. The significant difference is that while X.25 specifies the interface between a subscriber and the network, X.75 specifies the interface between two networks, and refers to these two STE as STE-X and STE-Y. This gives rise to some subtle differences in the protocol compared with X.25. For example, X.25 only allows network-generated reset and clearing causes to be passed from the network (DCE) to the subscriber (DTE), and not the other way around since the subscriber is not a network. However, at the interconnection of two X.25 networks, either network might reset or clear an X.25 call, so X.75 allows network-generated reset and clearing causes to be passed in either direction.
