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The first Electronic Switching Systems were not entirely digital. The Western Electric 1ESS switch still had reed relay metallic paths. It was stored-program-controlled.  Equipment testing, changes to phone numbers, circuit lockouts and similar tasks were accomplished by typing on a terminal.  Northern Telecom SP1, Ericsson AKE, Philips PRX/A, ITT Metaconta, British Telecom TXE series and several other designs were similar.  These systems could use the old electromechanical signaling methods inherited from crossbar and step-by-step switches.  They also introduced a new form of data communications: two 1ESS exchanges could communicate with one another using a data link called Common Channel Interoffice Signaling, (CCIS).  This data link was based on CCITT 6, a predecessor to SS7.