UNE-EN 301061-1V1.2.2

Integrated Services Digital Network (ISDN);Digital Subscriber Signalling System No. one (DSS1) protocol;Generic functional protocol for the support of supplementary services at the b" service entry point for Virtual Private Network (VPN) applications Part 1: Protocol specification" (Endorsed by Asociación Espanola de Normalización in August of 2021.)