| 摘要 |
In digital transmission systems, such as synchronous transmission systems according to the SDH/SONET standard, there is a need to have information on the synchronization status of the system. A known approach is to monitor the pointer activity. This is disadvantageous in that because of a hysteresis in the pointer processor, information derived from the pointer activity only conditionally reflects the synchronization status. In a network element (1) according to the invention which forms part of a transmission system of the above type, at least one interface unit (2, 3, 4) contains, besides an optical-to-electrical transducer (5), a synchronization-monitoring device (6) which derives a synchronization status parameter, e.g., TIE, RMSTIE, by comparing an external clock frequency (Te) with an internal clock frequency (Ti). For this, the synchronization-monitoring device (6) comprises a phase-comparing device (37), a memory device (25), and an evaluating device (26).
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