The access network and inter-exchange transport of the PSTN use synchronous optical transmission (SONET and SDH) technology, although some parts still use the older PDH technology.
PSTN中的接入网和内部交换台传送器采用的是同步光纤传输(SONET和SDH)技术，但也有某些地区仍采用过去的PD H技术。
The access network and inter-exchange transport of the PSTN use synchronous optical transmission (SONET and SDH) technology, although some parts still use the older PDH technology.
PSTN中的接入网和内部交换台传送器采用的是同步光纤传输(SONET和SDH)技术，但也有某些地区仍采用过去的PD H技术。
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