This paper outlines the concept and architecture of NGN and softswitch.And then presents three routing models of NGN according the current cases of NGN:no interoperability between softswitches

interoperability between softswitches and local server.The architecture of plain network is simple

so it is a very popular business model in the initial stage of NGN.With the development of NGN

interoperability between softswitches becomes more and more popular.For softswitches

any single call must pass though multiple switches to its destination by some definitely rules

so there will be a long time delay to establish a call.However

LS routing can send a call directly from initial softswitch to the destination.One of the key aspects is the introduction to the concept of TRIP

which can be the standard routing protocol in NGN.