Network architecture based on IMS can fulfill the access requirement of fixed network and the service requirement of future network

which plays a vital role in the Fixed Mobile Convergence （FMC） at core service control layer and supports multiple service of high layer

so IMS represents the development direction of future Next Generation Network （NGN）. This paper introduces the network framework and function architecture of TISPAN IMS

then analyzes the function and interface of TISPAN PSTN/ISDN Emulation Subsystem （PES）. In conclusion

we propose the extensible function architecture of TISPAN IMS.