Abstract: By formularized analysis of the function of the ideal packet networks, the Internet's limitation in guaranteeing QoS was presented, and the reason why the Internet cannot provide guaranteed QoS to interactive real time communication the was analyzed. Guaranteeing QoS required to design a novelty packet network architecture. Hereby,from the view of network architecture,the necessity that QoS-capable packet networks should do an expansion to the Internet archi tecture was proved, and the expansion contents were put forward.

Key words: Packet network, Architecture, QoS guaranteed, Design principles