Panel call indicator

Panel Call Indicator, or PCI, is a form of <a href="/facts/Signalling_(telecommunications)/6d4zgUj7">signalling</a> used between two <a href="/facts/Telephone_exchange/PaRpGm8I">telephone offices</a>. It was also originally called Relay Call Indicator (RCI).
Originally designed along with the <a href="/facts/Panel_switch/20edeFV1">panel type</a> telephone office, PCI was intended to allow subscribers in fully automated exchanges to <a href="/facts/Rotary_dial/Jrlloo2h">dial</a> numbers in <a href="/facts/Telephone_switchboard/Xu1xeItl">manual offices</a> the same way they dialed numbers in their own exchange. For PCI to achieve its purpose, the panel office sent the requested number to the manual office, where the number was lit on an operator's display. The <a href="/facts/Switchboard_operator/Ie7tNys3">switchboard operator</a> at a PCI-aware manual office reads the number from the call indicator display and completes the call in the usual way. As a format of interoffice signaling, PCI is one of multiple options retained for compatibility in the <a href="/facts/Number_Five_Crossbar_Switching_System/rPXbgU4C">#5 Crossbar switch</a>, a later system that served as the platform for the initial <a href="/facts/Dual-tone_multi-frequency_signaling/vg5vFo0X">DTMF</a> <a href="/facts/Push-button_telephone/6dybQS6M">push-button telephone</a> services.
In the British <a href="/facts/Director_telephone_system/Ka0d9s2t">Director telephone system</a>, Coded-Call Indicator working (CCI) filled a similar role, as it displayed dialed telephone numbers at the local manual exchange in a mixed (automatic and manual) <a href="/facts/Linked_numbering_scheme/RhDGetS4">linked-number area</a>.

Panel call indicator open-in-new

Panel call indicator