Telecom Regulatory Authority Of India - Subsection
Section 2(xiii) in The Telecommunication Interconnection Usage Charges Regulation, 2003
(xiii)"International Subscriber Dialing (ISD)" means the facility by which a subscriber can have direct connection between him (in India) with another end user in another country by means of direct dialing through licensed networks. This includes the coverage of the international sector by ILDO and the related national sector by NLDO and/or access provider.
