It is necessary to add VOIP gateways in access layer for interlinkage between the circuit switch network and IP network so that the traditional PSTN/ISDN users can access NGN smoothly and successfully.

• 为使传统PSTN/ISDN用户能顺利地向NGN过渡,需要在边缘接入层增加VOIP(Voice Over IP)网关来完成话音在电路交换网和IP网之间互通功能。