ITU-T E.157 PDF

This Recommendation provides guidance for international calling party number delivery, which is technology neutral. In this sense, this Recommendation is about the delivery of information from the call originating party, that is used for the determination of the origin of the call by the receiving party, irrespective of the network technology involved, e.g., whether calls are delivered over public switched telephone networks (PSTNs), Internet protocol (IP) based networks or any other type of public telecommunications network. The mechanism to assess the veracity of a particular calling party number is out of the scope of this Recommendation.

There appears to be a trend to suppress transmission across international boundaries of calling party numbers. Such practices may facilitate misuse of international numbering resources and create problems related to accountability and charging. This Recommendation provides guidance for the delivery of calling party numbers across different countries to improve their security (i.e., integrity) and minimize possible misuse, and risk of fraud and technical harm as called for by Article 42 of the Constitution.