This Recommendation primarily concerns privately switched networks for telephony. In certain circumstances these networks may be suitable for the transmission of analogue encoded data signals but no special arrangements have been made to ensure satisfactory performance in this respect. Although digital facilities on a portion of a circuit or digital switches may be employed, §§ 1-9 of this Recommendation mainly covers analogue interconnection of circuits and switches. §§ 10 and 11 cover some aspects of all digital connections.
ITU-T G.171-1993 history
1993ITU-T G.171-1993 TRANSMISSION PLAN ASPECTS OF PRIVATELY OPERATED NETWORKS