The Reference Manual begins by establishing the communication stack. Unlike modern RESTful APIs, NDC is a legacy, message-based protocol designed for reliability over slow serial connections (X.25 or SNA), though it now runs over TCP/IP.
Here, the manual shows the transition from Offer to Order. Unlike traditional PNRs, NDC creates a digital which includes: aptra advance ndc reference manual
It looks like you’re asking for a related to an “aptra advance ndc reference manual” — possibly for a software system, API, or aviation domain (given “NDC” often means New Distribution Capability in travel, or could be a command/control reference). NDC is a legacy