As the development of 6G accelerates

non-terrestrial networks (NTN) are emerging as a critical component to ensure seamless global coverage communication. This paper systematically reviews the evolution of the third-generation partnership project (3GPP) NTN standardization

from initial discussions in Release 15 to the in-depth optimizations in Release 19 and beyond. Through a detailed gap analysis

we identify key technical and industrial challenges across the wireless

network

and terminal domains that hinder the realization of a fully integrated space-terrestrial network. To address these challenges

we propose a 6G-oriented holistic architecture composed of three segments and three functional layers. We further outline essential enabling technologies

including networking technologies and intelligent resource management technologies. To validate the feasibility and effectiveness of the proposed architecture

we present a case study on integrated sensing and communication in high-speed mobility scenarios. Simulation results demonstrate significant performance gains in robustness

sensing accuracy

and adaptability compared to conventional approaches. Our findings establish a solid foundation for future research and standardization of 6G integrated networks

aiming to achieve intelligent

ubiquitous

and resilient communication infrastructures across space

air

and ground domains.