单项选择题
A. Each fiber has half of its capacity reserved for protection.
B. Two fibers carry their full capacities while the other two fibers are reserved for protection.
C. The signal is sent simultaneously in both directions around the ring. The receiver determines which fiber to listen to based on signal quality.
D. The signal is sent simultaneously in both directions around the ring. The transmitter determines which fiber has the working bit set for the receiver to acknowledge.
单项选择题 InSDH，whatisthenameoftheembeddedDataCommunicationChannel（DCC）inbytesD1-D3？（）
单项选择题 SDHCodeViolations（CVs）totalsinthePMtablesareactuallyanaccumulationofthenumberof（）.
多项选择题 Click the Exhibit button. The exhibit shows a 15454/15216 DWDM system and alarm indications. What are two possible sources of trouble shown in the system？（）