Information technology - International Standardized Profile TAnnnn - Connection-mode Transport Service over Connectionless-mode Network Service - Part 8: Security employing the Network Layer Security Protocol - Connection-mode with SDT-PDU based protection over X.25 packet switched data networks using virtual calls, for TA1111/TA1121 profiles (ISO/IEC DISP 10608-8:1996) prEN ISP 10608-8