These registers were provided in versions matching the signaling types the remote offices used.

Typically these included Multifrequency ('MF'; a 2-out-of-6 code that is not Touchtone); dial pulse ('DP'); and revertive pulsing ('RP'), a signaling system employed by panel offices.

A busy exchange might have 15 to 30 incoming registers, depending on trunking, and each is used only for the duration of interoffice signalling.