The existed transmissions have PDH and SDH transmission system, which are based on PSTN network. But as the future ATM network is going to be constructed, it is very necessary for ATM network to interwork with PSTN for telephony service. The international standardization organizations like ITU-T, ATM Forum offered CES, VTOA1, VTOA2 and so on for interworking with PSTN service, which spend many network resources and considerable transmission delay. So in this paper, new interworking PSTN for transmission will be proposed to lessen the transmission delay and the network resources.