PSA functions only on analog, hybrid, and digital communications protocol (DCP) telephones. Many types of DCP telephones exist, with different types and numbers of buttons. If you attempt to associate a DCP telephone or a hybrid telephone with a telephone that has incompatible buttons, button mapping is unpredictable. If you want the user to be able to use the terminal buttons and to have consistent displays, associate stations with terminals of the same type. Telephones and ports on different media servers or switches cannot be associated through PSA. Telephones on different switches, or nodes, within Distributed Communications Systems (DCS) cannot be associated through PSA. The system does not limit the number of stations that can use PSA. However, heavy use of the associate and dissociate functions can have a temporary impact on system performance.